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Influence of dynamic versus static core exercises on performance in field based fitness tests
Journal of Bodywork & Movement Therapies (2011) 15, 517e524
available at www.sciencedirect.com
journal homepage: www.elsevier.com/jbmt
EXERCISE PHYSIOLOGY RESEARCH
Influence of dynamic versus static core exercises on performance in field based fitness tests Kelly L. Parkhouse, BSc, ASCC a, Nick Ball, PhD, ASCC, CSCS b,* a b
Department of Sport and Exercise Science, University of Portsmouth, UK National Institute of Sports Studies, Faculty of Health, University of Canberra, ACT 2601, Australia
Received 5 July 2010; received in revised form 16 November 2010; accepted 30 November 2010
KEYWORDS Lumbopelvic; Stability ball; Performance
Summary Minimal evidence supports the claim that core stability training transfers into improved performance and the most effective training method to perform core exercises is still unknown. The purpose of the study was to compare the effects of a 6 week unstable static versus unstable dynamic core training program, on field based fitness tests. A static (n Z 6) and dynamic (n Z 6) training group performed two 45 min sessions per week for six weeks. Seven performance tests, consisting of three core (plank; double leg lowering; back extensions), one static (standing stork) and three dynamic (overhead medicine ball throw; vertical jump; 20 m sprint), were administered pre- and post training. Between group differences were assessed using a repeated measures MANOVA (P < 0.05). Both training groups improved in each of the core tests (P < 0.05). Neither training group demonstrated improvement in the dynamic field based tests (medicine ball throw, vertical jump height and 20 m sprint) (P > 0.05). Findings indicate that both types of training improved specific measures of core stability but did not transfer into any sport-related skill. Crown Copyright ª 2010 Published by Elsevier Ltd. All rights reserved.
Introduction Core stability training on unstable surfaces is commonplace in both healthcare and conditioning settings. Proponents of unstable training argue that such training enhances neuromuscular pathways (Beache and Earle, 2000; Hedrick, 2000), leading to greater strength (Behm et al., 2005; Gamble, 2007; * Corresponding author. Tel.: þ61 (0) 2 6201 2419; fax: þ61 (0) 2 6201 5615. E-mail address: [email protected] (N. Ball).
Rutherford and Jones, 1986; Vera-Garcia et al., 2000), power (Jeffreys, 2002) and balance (Anderson and Behm, 2005; Goodman, 2003; Lehman et al., 2005). Generally, findings have indicated that as the degree of instability increases, the degree of core muscle activity increases proportionally (Anderson and Behm, 2005; Behm et al., 2005; Marshall and Murphy, 2005; Murphy and Wilson, 1996; Vera-Garcia et al., 2000). For this reason, resistance exercises performed on unstable surfaces have been emphasized as most effective for the development of core stability (Boyle, 2004; Chek, 1999). Kibler et al. (2006) defined core stability as ‘the ability to control the position and motion of the trunk over the pelvis,
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518 thereby allowing optimum production, transfer and control of force and motion to the terminal segment in integrated athletic kinetic chain activities’. The role of core muscles in movement is varied according to the dynamics and postural demands of a given activity (Brown, 2006; Rogers, 2006). The core region can be divided into local and global groups (based on location and attachment site) (Johnson, 2002). Local muscles consist of small, deep muscles that control intersegmental motion between adjacent vertebrae (Johnson, 2002) and act as ‘stabilizers’ (Carter et al., 2006). Global muscles are large, superficial muscles that transfer force between the thoracic cage and pelvis and play a role in creating movement (Carter et al., 2006). As the core is central to most kinetic chains in sports movements, control of core strength, balance and motion will maximize the kinetic chains of upper and lower extremity function (Kibler et al., 2006), resulting in more efficient, stronger and powerful movements (Hedrick, 2000; McCurdy et al., 2005). Hence, there is an assumption that an improved core will increase one’s ability to run, jump, throw, strike and swing. There are two primary types of core training; static and dynamic training. Static training involves the joint and muscle either working against an immovable force (maximal muscle action) or being held in a static position while opposed by resistance (sub-maximal muscle action) (Siff, 2004). Actions within a wide variety of sports require isometric strength; for example, climbing, mountain biking, Judo, wrestling, gymnastics and horseback riding (Stone et al., 2003). Dynamic strength is the ability to exert a muscle force concentrically or eccentrically repeatedly or continuously over time. Due to the body’s functional design, during dynamic movement there is more dependence on core musculature than just skeletal rigidity as in a static situation; as the purpose of movement is to resist a force that changes its plane of motion (Siff, 2004). The surface the core exercise is performed on can also be varied to attempt to stimulate increased core activation through increased proprioceptive demands compared to floor based exercises (Cosio-Lima et al., 2003). Dynamic exercises performed on unstable surfaces are unable to reproduce the force and power outputs found when performing the same exercise on a stable surface (Anderson and Behm, 2005; Carter et al., 2006; McGill, 2001; Scibek et al., 2001) thus questioning the use of performing conventional exercises on unstable surfaces to enhance the transfer of training effect for the prescribed movement. However the transfer of training effect of dynamic core exercises into dynamic movements has not been investigated. There is disagreement amongst coaches about which type of strength is preferably developed for optimal performance (Plamondon et al., 1999; Stone et al., 2003). Past research has shown a positive transfer of training effect of dynamic exercises to dynamic tasks and static exercise to static tasks for non-core musculature (O’Shea and O’Shea, 1989). Several investigators also suggest that isometric forceetime characteristics are poorly correlated with dynamic performance (Haff et al., 2005; Murphy and Wilson, 1996). This indicates a limited transfer of training of static core exercises to dynamic performance. The use of field based fitness tests is an easy and convenient assessment method to allow coaches and users to track and monitor progress following an intervention (Winter
K.L. Parkhouse, N. Ball et al., 2007). The assessment of further neuromuscular and kinetic adaptations or transfer would require the use of specific technology such as electromyography (Winter et al., 2007), linear encoders (Harris et al., 2010) and force platforms (Winter et al., 2007) which are not freely available. The purpose of the study was to compare the effects of a 6week unstable static versus unstable dynamic core stability training program on core strength and other performance variables. Based on the principle of specificity, we predict a positive transfer of training effect of dynamic core exercise to the dynamic based tasks and a positive transfer of training effect of static core exercise to the static based tasks.
Methods Experimental approach to the problem This study involved a two group, two factor design to address whether a static or dynamic core stability ball intervention improved core and field based performance tests. Factor one was test, which had two levels: pre- and post testing. Factor two was training, which also had two levels: static or dynamic group. Dependent variables included 3 measurements of core performance (a static plank and double leg lowering test and a dynamic back extension test), 3 dynamic performance tests for speed (20 m sprint), lower body power (vertical jump), upper body power (overhead medicine ball throw) and a static balance test (standing stork).
Participants A group of 12 participants (6 male: 21.2 3.3 years; 174.5 6.3 cm; 78.7 3.7 kg, 6 female: 20.6 1.7 years; 172.6 4.7 cm; 67.7 2.3 kg) volunteered for the study. Informed consent was obtained and health history questionnaires were completed. All participants competed in University level sport >8 h per week and reported no history of acute or chronic low back injury prior to this experiment. All participants had prior experience of core stability exercises but had never undertaken a prescribed core stability program. Participants were asked to refrain from any other form of core specific exercises during the training period. Before commencement, the University Ethics review board approved the study. Participants were randomly assigned to either the static or dynamic core stability training group ensuring an equal gender split in each group.
Testing procedures Participants were instructed on how to perform each test and were allowed a familiarization period. Participants recorded their assessed test no less than 3 min following the familiarization period. Sufficient rest of at least 10 min was given between each test. Participants were told to put in maximal effort throughout each test whilst maintaining the correct position of the lumbar spine, with correct technique overseen by a qualified strength and conditioning coach. The battery of seven tests were completed 1 week prior to the training interventions and repeated one week after the training interventions. All tests were randomised for each participant to minimize learning effects.
Influence of dynamic versus static core exercises on performance in field based fitness tests
Static core tests Plank Participants were required to lie face down on a mat with their forearms and toes on the floor. On command, participants were asked to raise their hips off the floor to form a straight line from the shoulders to the heels, with a neutral back. Tests commenced once the correct position was assumed and discontinued when the position changed. A demonstration was shown and teaching points emphasized. The test was timed (s) using a stopwatch. Double leg lowering Participants laid with their back on a mat and knees to chest. After contracting the core region, they slowly slid both legs out into a straight position, with feet remaining 5 cm off the floor at all times. Participants were instructed to keep a neutral back for the duration of the test. Tests were discontinued when the body position changed or when legs became less than 180 to the body. The test was timed (s) using a stopwatch.
Dynamic core test Back extensions Participants were required to lay face down with hands at the temples. The number of repetitions performed was recorded in 2 min. They were encouraged to avoid lifting the feet off the floor to avoid the gluteus maximus aiding the lower back. A back extensor endurance test was used rather than a common curl-up test because there is only very low correlation of curl-up tests with core strength and endurance (Knudson, 2001), whereas back extensor tests give a better indication of lumbo-pelvic stability and strength.
Static field based test Standing stork (balance) Participants stood with hands on hips and were instructed to lift 1 leg and place the sole of the foot on the inner thigh of the other leg. On command, participants raised the heel of the straight leg to stand on the toes. Participants were required to balance for as long as possible without the heel of the foot touching the ground, or the other foot moving away from the knee. The test was repeated on the other leg. The test was timed (s) using a stopwatch.
Dynamic field based tests Overhead medicine ball throw (upper body power) Participants were required to kneel with the back erect, facing the throwing direction with their knees just behind the start line. With a 4 kg medicine ball grasped in both hands, participants were instructed to bring the ball back over the head and in 1 motion, throw the ball forwards and upwards with maximal power. It was emphasized that the spine must not be rotated and the favored arm must not be used to throw the arm. Stockbrugger and colleagues (Stockbrugger and Haennel, 2001) have shown this test to be a valid and reliable test for assessing explosive core and upper body power.
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Vertical jump (lower body power) Vertical jump height was taken from a static position with both feet together. Participants were instructed to place both hands on their hips and upon a verbal signal selfselected their depth for the countermovement jump. Participants were required to jump vertically as high as they could. The jump height was recorded (cm) using a vertical jump meter (Takei, Japan). 20 m sprint (speed) A straight 20 m line was measured and marked with cones. Light gates (Brower, UK) were positioned at both 0 m and 20 m. Participants were asked to start with their feet behind the start cone and to perform the task maximally. On the commands ‘take your marks’ and then ‘go’ participants were asked to sprint towards and the time gates at the 20 m mark. Time (s) was recorded from the timing gates.
Training procedure Each training group was required to attend two 45 min training sessions per week with a three day gap between each session. Three days prior to the commencement of the first training session, participants completed a familiarization session to ensure they were comfortable with the procedures and to minimize any learning effects. During this they practiced the concepts of ‘drawing in’ (neutralizing the spine and working the transverse abdominis and multifidus), correct postural control, the importance of breathing (Carter et al., 2006; Gamble, 2007) and stability ball balance (Goodman, 2003). Each participant was given a ball that was in accordance to their height. The size of the ball was conducive to achieving >90 angle at both the hip and knee (Goodman, 2003). The stability balls were 55, 65 or 75 cm in diameter. At the start of each training session, participants completed a thorough 10 min warm-up which included exercises such as jogging, skipping, but kicks and side stepping, followed by static stretching and specific lumbo-pelvic mobility exercises to reduce injury risk and lower back pain. Stretching was also completed upon completion of each session. All participants in both training groups completed 6 exercises per session. Overload was provided in the forms of increased duration and frequency (sets, reps, time under tension), increasing the complexity of exercises (adding opposite limb movements), increasing the lever arm of the exercises, altering the base of support and increased loading (external weights) (Gamble, 2007) (see Tables 1 and 2). The static group used a duration of 20 s or more when using submaximal loads (such as body weight) and 8e10 s with external resistance. The dynamic group performed 16 or more repetitions when using sub-maximal loads and 8e12 repetitions with external resistance. Exercises are based on previous references for core exercise prescription and were considered safe and effective (Cissik, 2002; Goodman, 2003; Hedrick, 2000; Lehman et al., 2005; Plamondon et al., 1999; Stanton et al., 2004; Vera-Garcia et al., 2000).
Statistical analyses On the completion of data collection, statistical analyses comprised of descriptive statistics to identify means and standard deviations for each variable of interest. The initial
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K.L. Parkhouse, N. Ball
Table 1
Static core stability program. Exercise, frequency, duration and applied progression and overload for each week.
Exercise
Week 1
Week 2
Week 3
Week 4
Week 5
Week 6
a
Time e secs (sets) Instruction
Time e secs (sets) Progression Time e secs (sets) Progression Time e secs (sets) Progression
Time e secs (sets) Progression Time e secs (sets) Progression
Side planka
Shoulder bridge
Full plank
Birddoga
Diagonal cruncha
Reverse hyperextension
25 (2)
30 (2)
25 (2)
30 (2)
20 (2)
15 (2)
On elbow, Top arm by side 35 (2)
Arms to side, feet wide, knees bent 45 (2)
Knees dropped, on elbows
1 leg only
Hands on knees
Hands by side
35 (2)
40 (2)
30 (2)
25 (2)
Increase time 25 (2)
Forearms up, increase time 35 (2)
Increase time
Increase time
35 (2)
30 (2)
Increase time 25 (2)
Increase time 35 (2)
Top arm in air 25 (2)
1 leg straight
On elbows, legs straight 45 (2)
Opposite arm & leg 40 (2)
Hands on chest 35 (2)
Arms on chest 45 (2)
Both legs straight, heels on ball
Increase time
Increase time
Increase time
Increase time
40 (2)
40 (2)
30 (2)
30 (2)
30 (2)
Arms off floor, increase time 40 (2)
On hands with legs straight 45 (2)
Both arms and 1 leg 40 (2)
Hands by temples 40 (2)
Hands by temples 40 (2)
Lift 1 leg off the ball
Increase time
Increase time
Increase time
Increase time
35 (2)
Bottom arm on hand, top arm by side 35 (2) Increase time 35 (2) Top arm in air
Z each side.
data was analyzed and it determined that data was parametric. Therefore, A 2 2 (static, dynamic test time) multivariate analysis of variance (MANOVA) with repeated measures was performed to determine the effect of training
Table 2
Dynamic core stability program. Exercise, frequency, duration and applied progression and overload for each week.
Exercise
Jack knife
Russian twista
Reverse hyperextension
Lateral rolla
Hip crossovera
Reverse crunch
8 (2) Hands together, wide feet 10 (2) Increase reps 10 (2) Narrow feet 12 (2) Increase reps
25 (2) Arms by side
8 (2) Wide feet
8 (2) Arms by side
20 (2) Arms on knees
35 (2) Increase reps 35 (2) Hands on chest 45 (2) Increase reps
12 (2) Increase reps 12 (2) Narrow feet 8 (2) Increase reps
30 (2) Increase reps 25 (2) Arms on chest 35 (2) Increase reps
10 (2) Add weight plate 12 (2) Increase reps
40 (2) Arms in front
10 (2) Lift 1 leg
10 (2) Increase reps 12 (2) Increase reps 8 (2) Elbows up, hands on chest 10 (2) Increase reps
45 (2) Increase reps
12 (2) Increase reps
12 (2) Increase reps
Week 1
Reps (sets) Instruction
Week 2
Reps (sets) Progression Reps (sets) Progression Reps (sets) Progression
8 (2) Hands wide, knees on ball 12 (2) Increase reps 12 (2) Hands narrow 8 (2) Toes on ball
Week 5
Reps (sets) Progression
12 (2) Increase reps
Week 6
Reps (sets) Progression
16 (2) Increase reps
Week 3 Week 4
a
on each parameter measured. Independent variables were gender, age and training type. Mauchly’s test of sphericity revealed that my data remained normally distributed across all time points (P > 0.05). Where a main effect was observed,
Z each side.
30 (2) Hands by temples 40 (2) Increase reps
Influence of dynamic versus static core exercises on performance in field based fitness tests a least significant difference (LSD) post hoc analysis was conducted to identify the source of the difference (P < 0.05). Further analysis of the data was carried out using Pearson’s correlation coefficient which identified inter-relationships between all test variables. All statistical analysis was carried out using SPSS for windows version 14. Intra-subject reliability was based on the vertical jump scores with an intraclass correlation coefficient of 0.95 obtained.
Results Static/dynamic core and field based tests Table 3 presents the results of each core and field based test for both training groups before and after 6 weeks of training. The mean scores of the dynamic core training group were improved at the post-test in six out of the seven functional tests; however the mean scores of the static core training group only showed improvement in five out of seven tests. Both groups improved in all core based tests (Static Group e Plank: F (1 10) Z 11.755, P Z 0.000; Double leg lowering: F (1 10) Z 1.04, P Z 0.000; Back Extension: F (1 10) Z 97.5, P Z 0.006; Dynamic Group e Plank: F (1 10) Z 81.8, P Z 0.000; Double leg lowering: F (1 10) Z 40.1, P Z 0.000; Back Extension: F (1 10) Z 16.64, P Z 0.002). Post Hoc LSD found the
521
dynamic training group to show greater improvements than the static group in all 3 core tests (P < 0.05). No improvements were found in any of the dynamic tests for both static and dynamic groups (P > 0.05). However, standing stork scores increased in the static group post training (F1 10 Z 1.16, P Z 0.000) (Fig. 1). For the static training group, Pearson’s Correlation coefficient found strong positive relationships between the plank/double leg lowering test (0.817), plank/vertical jump height (0.821), and standing stork/double leg lowering test (0.820). Very strong negative relationships were found for the plank/20 m sprint test (0.927), and double leg lowering/20m sprint test (0.822). The dynamic training group was found to have strong positive relationships between the plank/20 m sprint test (0.942), and moderately strong positive relationships between medicine ball throw/back extensions (0.805) and between 20 m sprint/ vertical jump height (0.794).
Discussion The purpose of the study was to compare the effects of a 6 week core stability training program with exercises performed on an unstable surface on field based performance tests. This study suggests that 6 weeks of both static and
Table 3 Static and dynamic core and field based test results after 6 weeks of training for both static and dynamic training groups (means SD). Static indicates the group that performed a static core training program; Dynamic indicates that the group performed a dynamic core training program. n Static core tests Plank (sec) Static 6 Dynamic 6 Double leg lowering (sec) Static 6 Dynamic 6 Dynamic core tests Back extension (reps) Static 6 Dynamic 6 Static field based tests Standing stork (sec) Static 6 Dynamic 6 Dynamic field based tests Vertical jump (cm) Dynamic 6 Static 6 20 m Sprint (sec) Static 6 Dynamic 6 Medicine ball throw (m) Static 6 Dynamic 6 NS Z P > 0.05. * Z P < 0.01. * Z P < 0.001.
Pre
Post
% Difference
p
59.0 4.69 51.76 4.43
64.0 4.6 63.8 5.04
8.5% 23.3%
** **
25.65 2.62 24.68 2.45
28.18 3.78 35.43 2.58
9.9% 43.6%
** **
67.00 4.34 65.60 2.16
77.80 2.64 70.10 1.94
14.9% 45.8%
* *
3.98 0.17 4.42 0.43
6.55 0.44 4.80 0.48
64.5% 8.6%
** NS
33.4 1.92 32.9 1.36
32.7 2.16 34.7 1.75
0.9% 6.1%
NS NS
5.56 0.48 5.51 0.31
5.50 0.30 5.59 0.41
1.1% 1.4%
NS NS
3.48 0.36 3.53 0.22
3.58 0.26 3.5 0.22
2.9% 0.8%
NS NS
522
Figure 1 Mean pre- and post training standing stork scores for both groups (N Z 12).
dynamic type core training improves core performance (P < 0.05). However, no transfer of training effect to the dynamic tests was shown (P > 0.05). This is the first empirical study to examine the effect of static versus dynamic core stability ball training on physical performance. While core stability ball training remains a popular adjunct to training for many athletes and anecdotal evidence supports its widespread use, results of this study appear to be consistent with previous research which has found no transfer of training effect (Nesser et al., 2008; Scibek et al., 2001; Tse et al., 2005). The static training group had a significant transfer into the balance test, which accepts part of our hypothesis and is similar to previous research. Rutherford and Jones (Rutherford and Jones, 1986) found that early adaptations in short term static core training resulted in greater gains in torso balance. Supporters of instability training propose the neuromuscular system is challenged to a greater extent and increases proprioceptive demands (Rutherford and Jones, 1986). The unstable nature of the ball forces one to make postural adjustments to increase co-ordination, which require activation of the appropriate core musculature to stabilize the lumbar spine. The deep postural muscles of the trunk have a primary purpose to ensure this lumbar stabilization and to maintain the body’s centre of gravity within its base of support to minimize loss of balance (Anderson and Behm, 2005). However, although static core training has proved effective in a measure of static balance, more sports specific research may be needed to clarify this transfer. No improvements were found in the overhead medicine ball throw, 20 m sprint and vertical jump height scores post both static and dynamic training. These results provide no support for the proposal of a more enhanced and efficient transfer of energy due to an enhanced core. Therefore we reject part of our hypothesis in that dynamic exercise will demonstrate a positive transfer of training effect to dynamic tasks. This is in agreement with Scibek and colleagues (Scibek et al., 2001) who looked at the effect of Swiss ball core stability training on subsequent swim performance. Their results showed enhanced core strength in static exercises
K.L. Parkhouse, N. Ball however no improvements in swim performance. Furthermore Nesser and colleagues (Nesser et al., 2008) showed no correlation of core strength to strength and power measures in collegiate athletes. This indicates that power performance may not be affected by core strength refuting previous claims. However core training has been shown to improve 5,000 m run times (Sato and Mokha, 2009) indicating that core training modalities may have a better transfer to more endurance based events in the resistance of fatigue and maintenance of posture (Brumitt, 2004). Stanton and colleagues (Stanton et al., 2004) showed no improvement in running economy, however did not include a timed measure for the run trials performed. These studies and the current study’s findings support the notion that core training emphasizes local muscle adaptation and core strength without concomitant improvements in power based physical performance. Although the outcomes appear clear, it must be highlighted that only 12 participants were used in the study. We suggest that any future studies in this area should include a much larger sample size to ensure sound reliability of results. Furthermore, the transfer of training effect of the dynamic core exercises to the dynamic movements may have required a longer duration training program or an increased frequency of sessions. Early phase adaptations including increased stability, neuromuscular activity and proprioceptor activity have been shown after 5 weeks of training doing abdominal and one lower back exercise per day (Cosio-Lima et al., 2003), however these improvements were shown mainly in neuromuscular changes opposed to strength changes as measured by isokinetic testing. Thus the neuromuscular control and co-ordination trained by core dynamic exercises may only improve muscular recruitment in the initial phases opposed to the transferring into an external measure. Thus the benefits of the core training program here for the dynamic exercise may not be transfer into performance measures but may potentially improve kinematic and kinetic measures. Alongside program duration the nature of the exercise used may be changed for athletes with free weight exercises using moderate levels of instability may be more suitable to maintain specificity (Behm et al., 2010). The concept of specificity suggests that quick, explosive dynamic performance variables are likely to be improved by similar type training actions. To train improved speed of force application more importance is placed on performing the exercise powerfully compared to the selection of the exercise movement (Behm and Sale, 1993). Although dynamic exercises were performed by the dynamic training group, explosive power and high rates of force development were not emphasized and subsequently not transferred over. A lower repetition range with emphasis on increased speed of movement whilst maintaining lumbo-pelvic stability may have seen a better transfer into the sprint, jump and throw tests as the core would be trained in a similar manner to its use within these tests. The loading measures used in this study may not have been sufficient to improve core muscle function during dynamic exercises. Hibbs and colleagues (Hibbs et al., 2008) suggested that the cores are trained more for everyday requirements (low loads, slow movements) opposed to an athlete requirement of high load and resistive movements. The population group in this study
Influence of dynamic versus static core exercises on performance in field based fitness tests indicated a better use of their core strength in static movements compared to the high force dynamic field tests. In summary, the results of this study suggest that 6 weeks of stability ball training doesn’t improve dynamic field based performance tests based on the sample size used. The benefits of core training may reside in long term athlete development programmes whereby appropriate posture and core strength may transfer into improved co-ordination and exercise performance. Increases in training duration and speed of movement in dynamic core exercises may provide a more specific stimulus of the core for transfer into dynamic field based movements, however this warrants further investigation.
Practical applications The current study shows that both static and dynamic core stability exercises trained over a 6-week period are able to effectively increase the core strength of participants. These strength benefits do not transfer into improved dynamic performance in sprinting, throwing and jumping. The study indicates that short term training may only improve core strength by reducing fatigue in the core musculature and allowing the athlete more neuromuscular control during balance. A program that incorporates both static and dynamic exercises may provide these benefits if the dynamic exercises are then performed with increased velocity. This may improve the transfer of training effect into dynamic performance. It must be understood that the findings may only be applicable to the population under investigation and the effects on elite athletes is unknown. However due to the assumed improved core strength and physicality of elite performers it can be assumed that their scope for adaptation is smaller than the current population and thus non-significant finding for core transfer into dynamic performance can be reasonably assumed. Findings do not discourage the use of core stability ball training; instead, they suggest that specificity on the rate of force development, speed and power of each core exercise may be needed to transfer into sporting performance.
Acknowledgements Sincere thanks to all the participants who devoted their time and effort to this study.
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K.L. Parkhouse, N. Ball Stanton, R., Reaburn, P.R., Humpries, B., 2004. The effect of short-term Swiss ball training on core stability and running economy. Journal of Strength and Conditioning Research 18, 522e528. Stockbrugger, B.A., Haennel, R.G., 2001. Validity and reliability of a medicine ball explosive power test. Journal of Strength and Conditioning Research 15, 431e438. Stone, M.H., Sanborn, K., O’Bryant, H.S., Hartman, M., Stone, M.E., Proulx, C., Ward, B., Hruby, J., 2003. Maximum strength-power-performance relationships in collegiate throwers. Journal of Strength and Conditioning Research 17, 739e745. Tse, M.A., McManus, A.M., Masters, R.S., 2005. Development and validation of a core endurance intervention program: implications for performance in college-age rowers. Journal of Strength and Conditioning Research 19, 547e552. Vera-Garcia, F.J., Grenier, S.G., McGill, S.M., 2000. Abdominal muscle response during curl-ups on both stable and labile surfaces. Physical Therapy 80, 564e569. Winter, E.M., Jones, A.M., Davison, R., Bromley, P.D., Mercer, T., 2007. Sport and Exercise Physiology Testing Guidelines: Exercise and Clinical Testing. Routledge, USA.
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EXERCISE PHYSIOLOGY RESEARCH
Influence of dynamic versus static core exercises on performance in field based fitness tests Kelly L. Parkhouse, BSc, ASCC a, Nick Ball, PhD, ASCC, CSCS b,* a b
Department of Sport and Exercise Science, University of Portsmouth, UK National Institute of Sports Studies, Faculty of Health, University of Canberra, ACT 2601, Australia
Received 5 July 2010; received in revised form 16 November 2010; accepted 30 November 2010
KEYWORDS Lumbopelvic; Stability ball; Performance
Summary Minimal evidence supports the claim that core stability training transfers into improved performance and the most effective training method to perform core exercises is still unknown. The purpose of the study was to compare the effects of a 6 week unstable static versus unstable dynamic core training program, on field based fitness tests. A static (n Z 6) and dynamic (n Z 6) training group performed two 45 min sessions per week for six weeks. Seven performance tests, consisting of three core (plank; double leg lowering; back extensions), one static (standing stork) and three dynamic (overhead medicine ball throw; vertical jump; 20 m sprint), were administered pre- and post training. Between group differences were assessed using a repeated measures MANOVA (P < 0.05). Both training groups improved in each of the core tests (P < 0.05). Neither training group demonstrated improvement in the dynamic field based tests (medicine ball throw, vertical jump height and 20 m sprint) (P > 0.05). Findings indicate that both types of training improved specific measures of core stability but did not transfer into any sport-related skill. Crown Copyright ª 2010 Published by Elsevier Ltd. All rights reserved.
Introduction Core stability training on unstable surfaces is commonplace in both healthcare and conditioning settings. Proponents of unstable training argue that such training enhances neuromuscular pathways (Beache and Earle, 2000; Hedrick, 2000), leading to greater strength (Behm et al., 2005; Gamble, 2007; * Corresponding author. Tel.: þ61 (0) 2 6201 2419; fax: þ61 (0) 2 6201 5615. E-mail address: [email protected] (N. Ball).
Rutherford and Jones, 1986; Vera-Garcia et al., 2000), power (Jeffreys, 2002) and balance (Anderson and Behm, 2005; Goodman, 2003; Lehman et al., 2005). Generally, findings have indicated that as the degree of instability increases, the degree of core muscle activity increases proportionally (Anderson and Behm, 2005; Behm et al., 2005; Marshall and Murphy, 2005; Murphy and Wilson, 1996; Vera-Garcia et al., 2000). For this reason, resistance exercises performed on unstable surfaces have been emphasized as most effective for the development of core stability (Boyle, 2004; Chek, 1999). Kibler et al. (2006) defined core stability as ‘the ability to control the position and motion of the trunk over the pelvis,
1360-8592/$ - see front matter Crown Copyright ª 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.jbmt.2010.12.001
518 thereby allowing optimum production, transfer and control of force and motion to the terminal segment in integrated athletic kinetic chain activities’. The role of core muscles in movement is varied according to the dynamics and postural demands of a given activity (Brown, 2006; Rogers, 2006). The core region can be divided into local and global groups (based on location and attachment site) (Johnson, 2002). Local muscles consist of small, deep muscles that control intersegmental motion between adjacent vertebrae (Johnson, 2002) and act as ‘stabilizers’ (Carter et al., 2006). Global muscles are large, superficial muscles that transfer force between the thoracic cage and pelvis and play a role in creating movement (Carter et al., 2006). As the core is central to most kinetic chains in sports movements, control of core strength, balance and motion will maximize the kinetic chains of upper and lower extremity function (Kibler et al., 2006), resulting in more efficient, stronger and powerful movements (Hedrick, 2000; McCurdy et al., 2005). Hence, there is an assumption that an improved core will increase one’s ability to run, jump, throw, strike and swing. There are two primary types of core training; static and dynamic training. Static training involves the joint and muscle either working against an immovable force (maximal muscle action) or being held in a static position while opposed by resistance (sub-maximal muscle action) (Siff, 2004). Actions within a wide variety of sports require isometric strength; for example, climbing, mountain biking, Judo, wrestling, gymnastics and horseback riding (Stone et al., 2003). Dynamic strength is the ability to exert a muscle force concentrically or eccentrically repeatedly or continuously over time. Due to the body’s functional design, during dynamic movement there is more dependence on core musculature than just skeletal rigidity as in a static situation; as the purpose of movement is to resist a force that changes its plane of motion (Siff, 2004). The surface the core exercise is performed on can also be varied to attempt to stimulate increased core activation through increased proprioceptive demands compared to floor based exercises (Cosio-Lima et al., 2003). Dynamic exercises performed on unstable surfaces are unable to reproduce the force and power outputs found when performing the same exercise on a stable surface (Anderson and Behm, 2005; Carter et al., 2006; McGill, 2001; Scibek et al., 2001) thus questioning the use of performing conventional exercises on unstable surfaces to enhance the transfer of training effect for the prescribed movement. However the transfer of training effect of dynamic core exercises into dynamic movements has not been investigated. There is disagreement amongst coaches about which type of strength is preferably developed for optimal performance (Plamondon et al., 1999; Stone et al., 2003). Past research has shown a positive transfer of training effect of dynamic exercises to dynamic tasks and static exercise to static tasks for non-core musculature (O’Shea and O’Shea, 1989). Several investigators also suggest that isometric forceetime characteristics are poorly correlated with dynamic performance (Haff et al., 2005; Murphy and Wilson, 1996). This indicates a limited transfer of training of static core exercises to dynamic performance. The use of field based fitness tests is an easy and convenient assessment method to allow coaches and users to track and monitor progress following an intervention (Winter
K.L. Parkhouse, N. Ball et al., 2007). The assessment of further neuromuscular and kinetic adaptations or transfer would require the use of specific technology such as electromyography (Winter et al., 2007), linear encoders (Harris et al., 2010) and force platforms (Winter et al., 2007) which are not freely available. The purpose of the study was to compare the effects of a 6week unstable static versus unstable dynamic core stability training program on core strength and other performance variables. Based on the principle of specificity, we predict a positive transfer of training effect of dynamic core exercise to the dynamic based tasks and a positive transfer of training effect of static core exercise to the static based tasks.
Methods Experimental approach to the problem This study involved a two group, two factor design to address whether a static or dynamic core stability ball intervention improved core and field based performance tests. Factor one was test, which had two levels: pre- and post testing. Factor two was training, which also had two levels: static or dynamic group. Dependent variables included 3 measurements of core performance (a static plank and double leg lowering test and a dynamic back extension test), 3 dynamic performance tests for speed (20 m sprint), lower body power (vertical jump), upper body power (overhead medicine ball throw) and a static balance test (standing stork).
Participants A group of 12 participants (6 male: 21.2 3.3 years; 174.5 6.3 cm; 78.7 3.7 kg, 6 female: 20.6 1.7 years; 172.6 4.7 cm; 67.7 2.3 kg) volunteered for the study. Informed consent was obtained and health history questionnaires were completed. All participants competed in University level sport >8 h per week and reported no history of acute or chronic low back injury prior to this experiment. All participants had prior experience of core stability exercises but had never undertaken a prescribed core stability program. Participants were asked to refrain from any other form of core specific exercises during the training period. Before commencement, the University Ethics review board approved the study. Participants were randomly assigned to either the static or dynamic core stability training group ensuring an equal gender split in each group.
Testing procedures Participants were instructed on how to perform each test and were allowed a familiarization period. Participants recorded their assessed test no less than 3 min following the familiarization period. Sufficient rest of at least 10 min was given between each test. Participants were told to put in maximal effort throughout each test whilst maintaining the correct position of the lumbar spine, with correct technique overseen by a qualified strength and conditioning coach. The battery of seven tests were completed 1 week prior to the training interventions and repeated one week after the training interventions. All tests were randomised for each participant to minimize learning effects.
Influence of dynamic versus static core exercises on performance in field based fitness tests
Static core tests Plank Participants were required to lie face down on a mat with their forearms and toes on the floor. On command, participants were asked to raise their hips off the floor to form a straight line from the shoulders to the heels, with a neutral back. Tests commenced once the correct position was assumed and discontinued when the position changed. A demonstration was shown and teaching points emphasized. The test was timed (s) using a stopwatch. Double leg lowering Participants laid with their back on a mat and knees to chest. After contracting the core region, they slowly slid both legs out into a straight position, with feet remaining 5 cm off the floor at all times. Participants were instructed to keep a neutral back for the duration of the test. Tests were discontinued when the body position changed or when legs became less than 180 to the body. The test was timed (s) using a stopwatch.
Dynamic core test Back extensions Participants were required to lay face down with hands at the temples. The number of repetitions performed was recorded in 2 min. They were encouraged to avoid lifting the feet off the floor to avoid the gluteus maximus aiding the lower back. A back extensor endurance test was used rather than a common curl-up test because there is only very low correlation of curl-up tests with core strength and endurance (Knudson, 2001), whereas back extensor tests give a better indication of lumbo-pelvic stability and strength.
Static field based test Standing stork (balance) Participants stood with hands on hips and were instructed to lift 1 leg and place the sole of the foot on the inner thigh of the other leg. On command, participants raised the heel of the straight leg to stand on the toes. Participants were required to balance for as long as possible without the heel of the foot touching the ground, or the other foot moving away from the knee. The test was repeated on the other leg. The test was timed (s) using a stopwatch.
Dynamic field based tests Overhead medicine ball throw (upper body power) Participants were required to kneel with the back erect, facing the throwing direction with their knees just behind the start line. With a 4 kg medicine ball grasped in both hands, participants were instructed to bring the ball back over the head and in 1 motion, throw the ball forwards and upwards with maximal power. It was emphasized that the spine must not be rotated and the favored arm must not be used to throw the arm. Stockbrugger and colleagues (Stockbrugger and Haennel, 2001) have shown this test to be a valid and reliable test for assessing explosive core and upper body power.
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Vertical jump (lower body power) Vertical jump height was taken from a static position with both feet together. Participants were instructed to place both hands on their hips and upon a verbal signal selfselected their depth for the countermovement jump. Participants were required to jump vertically as high as they could. The jump height was recorded (cm) using a vertical jump meter (Takei, Japan). 20 m sprint (speed) A straight 20 m line was measured and marked with cones. Light gates (Brower, UK) were positioned at both 0 m and 20 m. Participants were asked to start with their feet behind the start cone and to perform the task maximally. On the commands ‘take your marks’ and then ‘go’ participants were asked to sprint towards and the time gates at the 20 m mark. Time (s) was recorded from the timing gates.
Training procedure Each training group was required to attend two 45 min training sessions per week with a three day gap between each session. Three days prior to the commencement of the first training session, participants completed a familiarization session to ensure they were comfortable with the procedures and to minimize any learning effects. During this they practiced the concepts of ‘drawing in’ (neutralizing the spine and working the transverse abdominis and multifidus), correct postural control, the importance of breathing (Carter et al., 2006; Gamble, 2007) and stability ball balance (Goodman, 2003). Each participant was given a ball that was in accordance to their height. The size of the ball was conducive to achieving >90 angle at both the hip and knee (Goodman, 2003). The stability balls were 55, 65 or 75 cm in diameter. At the start of each training session, participants completed a thorough 10 min warm-up which included exercises such as jogging, skipping, but kicks and side stepping, followed by static stretching and specific lumbo-pelvic mobility exercises to reduce injury risk and lower back pain. Stretching was also completed upon completion of each session. All participants in both training groups completed 6 exercises per session. Overload was provided in the forms of increased duration and frequency (sets, reps, time under tension), increasing the complexity of exercises (adding opposite limb movements), increasing the lever arm of the exercises, altering the base of support and increased loading (external weights) (Gamble, 2007) (see Tables 1 and 2). The static group used a duration of 20 s or more when using submaximal loads (such as body weight) and 8e10 s with external resistance. The dynamic group performed 16 or more repetitions when using sub-maximal loads and 8e12 repetitions with external resistance. Exercises are based on previous references for core exercise prescription and were considered safe and effective (Cissik, 2002; Goodman, 2003; Hedrick, 2000; Lehman et al., 2005; Plamondon et al., 1999; Stanton et al., 2004; Vera-Garcia et al., 2000).
Statistical analyses On the completion of data collection, statistical analyses comprised of descriptive statistics to identify means and standard deviations for each variable of interest. The initial
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K.L. Parkhouse, N. Ball
Table 1
Static core stability program. Exercise, frequency, duration and applied progression and overload for each week.
Exercise
Week 1
Week 2
Week 3
Week 4
Week 5
Week 6
a
Time e secs (sets) Instruction
Time e secs (sets) Progression Time e secs (sets) Progression Time e secs (sets) Progression
Time e secs (sets) Progression Time e secs (sets) Progression
Side planka
Shoulder bridge
Full plank
Birddoga
Diagonal cruncha
Reverse hyperextension
25 (2)
30 (2)
25 (2)
30 (2)
20 (2)
15 (2)
On elbow, Top arm by side 35 (2)
Arms to side, feet wide, knees bent 45 (2)
Knees dropped, on elbows
1 leg only
Hands on knees
Hands by side
35 (2)
40 (2)
30 (2)
25 (2)
Increase time 25 (2)
Forearms up, increase time 35 (2)
Increase time
Increase time
35 (2)
30 (2)
Increase time 25 (2)
Increase time 35 (2)
Top arm in air 25 (2)
1 leg straight
On elbows, legs straight 45 (2)
Opposite arm & leg 40 (2)
Hands on chest 35 (2)
Arms on chest 45 (2)
Both legs straight, heels on ball
Increase time
Increase time
Increase time
Increase time
40 (2)
40 (2)
30 (2)
30 (2)
30 (2)
Arms off floor, increase time 40 (2)
On hands with legs straight 45 (2)
Both arms and 1 leg 40 (2)
Hands by temples 40 (2)
Hands by temples 40 (2)
Lift 1 leg off the ball
Increase time
Increase time
Increase time
Increase time
35 (2)
Bottom arm on hand, top arm by side 35 (2) Increase time 35 (2) Top arm in air
Z each side.
data was analyzed and it determined that data was parametric. Therefore, A 2 2 (static, dynamic test time) multivariate analysis of variance (MANOVA) with repeated measures was performed to determine the effect of training
Table 2
Dynamic core stability program. Exercise, frequency, duration and applied progression and overload for each week.
Exercise
Jack knife
Russian twista
Reverse hyperextension
Lateral rolla
Hip crossovera
Reverse crunch
8 (2) Hands together, wide feet 10 (2) Increase reps 10 (2) Narrow feet 12 (2) Increase reps
25 (2) Arms by side
8 (2) Wide feet
8 (2) Arms by side
20 (2) Arms on knees
35 (2) Increase reps 35 (2) Hands on chest 45 (2) Increase reps
12 (2) Increase reps 12 (2) Narrow feet 8 (2) Increase reps
30 (2) Increase reps 25 (2) Arms on chest 35 (2) Increase reps
10 (2) Add weight plate 12 (2) Increase reps
40 (2) Arms in front
10 (2) Lift 1 leg
10 (2) Increase reps 12 (2) Increase reps 8 (2) Elbows up, hands on chest 10 (2) Increase reps
45 (2) Increase reps
12 (2) Increase reps
12 (2) Increase reps
Week 1
Reps (sets) Instruction
Week 2
Reps (sets) Progression Reps (sets) Progression Reps (sets) Progression
8 (2) Hands wide, knees on ball 12 (2) Increase reps 12 (2) Hands narrow 8 (2) Toes on ball
Week 5
Reps (sets) Progression
12 (2) Increase reps
Week 6
Reps (sets) Progression
16 (2) Increase reps
Week 3 Week 4
a
on each parameter measured. Independent variables were gender, age and training type. Mauchly’s test of sphericity revealed that my data remained normally distributed across all time points (P > 0.05). Where a main effect was observed,
Z each side.
30 (2) Hands by temples 40 (2) Increase reps
Influence of dynamic versus static core exercises on performance in field based fitness tests a least significant difference (LSD) post hoc analysis was conducted to identify the source of the difference (P < 0.05). Further analysis of the data was carried out using Pearson’s correlation coefficient which identified inter-relationships between all test variables. All statistical analysis was carried out using SPSS for windows version 14. Intra-subject reliability was based on the vertical jump scores with an intraclass correlation coefficient of 0.95 obtained.
Results Static/dynamic core and field based tests Table 3 presents the results of each core and field based test for both training groups before and after 6 weeks of training. The mean scores of the dynamic core training group were improved at the post-test in six out of the seven functional tests; however the mean scores of the static core training group only showed improvement in five out of seven tests. Both groups improved in all core based tests (Static Group e Plank: F (1 10) Z 11.755, P Z 0.000; Double leg lowering: F (1 10) Z 1.04, P Z 0.000; Back Extension: F (1 10) Z 97.5, P Z 0.006; Dynamic Group e Plank: F (1 10) Z 81.8, P Z 0.000; Double leg lowering: F (1 10) Z 40.1, P Z 0.000; Back Extension: F (1 10) Z 16.64, P Z 0.002). Post Hoc LSD found the
521
dynamic training group to show greater improvements than the static group in all 3 core tests (P < 0.05). No improvements were found in any of the dynamic tests for both static and dynamic groups (P > 0.05). However, standing stork scores increased in the static group post training (F1 10 Z 1.16, P Z 0.000) (Fig. 1). For the static training group, Pearson’s Correlation coefficient found strong positive relationships between the plank/double leg lowering test (0.817), plank/vertical jump height (0.821), and standing stork/double leg lowering test (0.820). Very strong negative relationships were found for the plank/20 m sprint test (0.927), and double leg lowering/20m sprint test (0.822). The dynamic training group was found to have strong positive relationships between the plank/20 m sprint test (0.942), and moderately strong positive relationships between medicine ball throw/back extensions (0.805) and between 20 m sprint/ vertical jump height (0.794).
Discussion The purpose of the study was to compare the effects of a 6 week core stability training program with exercises performed on an unstable surface on field based performance tests. This study suggests that 6 weeks of both static and
Table 3 Static and dynamic core and field based test results after 6 weeks of training for both static and dynamic training groups (means SD). Static indicates the group that performed a static core training program; Dynamic indicates that the group performed a dynamic core training program. n Static core tests Plank (sec) Static 6 Dynamic 6 Double leg lowering (sec) Static 6 Dynamic 6 Dynamic core tests Back extension (reps) Static 6 Dynamic 6 Static field based tests Standing stork (sec) Static 6 Dynamic 6 Dynamic field based tests Vertical jump (cm) Dynamic 6 Static 6 20 m Sprint (sec) Static 6 Dynamic 6 Medicine ball throw (m) Static 6 Dynamic 6 NS Z P > 0.05. * Z P < 0.01. * Z P < 0.001.
Pre
Post
% Difference
p
59.0 4.69 51.76 4.43
64.0 4.6 63.8 5.04
8.5% 23.3%
** **
25.65 2.62 24.68 2.45
28.18 3.78 35.43 2.58
9.9% 43.6%
** **
67.00 4.34 65.60 2.16
77.80 2.64 70.10 1.94
14.9% 45.8%
* *
3.98 0.17 4.42 0.43
6.55 0.44 4.80 0.48
64.5% 8.6%
** NS
33.4 1.92 32.9 1.36
32.7 2.16 34.7 1.75
0.9% 6.1%
NS NS
5.56 0.48 5.51 0.31
5.50 0.30 5.59 0.41
1.1% 1.4%
NS NS
3.48 0.36 3.53 0.22
3.58 0.26 3.5 0.22
2.9% 0.8%
NS NS
522
Figure 1 Mean pre- and post training standing stork scores for both groups (N Z 12).
dynamic type core training improves core performance (P < 0.05). However, no transfer of training effect to the dynamic tests was shown (P > 0.05). This is the first empirical study to examine the effect of static versus dynamic core stability ball training on physical performance. While core stability ball training remains a popular adjunct to training for many athletes and anecdotal evidence supports its widespread use, results of this study appear to be consistent with previous research which has found no transfer of training effect (Nesser et al., 2008; Scibek et al., 2001; Tse et al., 2005). The static training group had a significant transfer into the balance test, which accepts part of our hypothesis and is similar to previous research. Rutherford and Jones (Rutherford and Jones, 1986) found that early adaptations in short term static core training resulted in greater gains in torso balance. Supporters of instability training propose the neuromuscular system is challenged to a greater extent and increases proprioceptive demands (Rutherford and Jones, 1986). The unstable nature of the ball forces one to make postural adjustments to increase co-ordination, which require activation of the appropriate core musculature to stabilize the lumbar spine. The deep postural muscles of the trunk have a primary purpose to ensure this lumbar stabilization and to maintain the body’s centre of gravity within its base of support to minimize loss of balance (Anderson and Behm, 2005). However, although static core training has proved effective in a measure of static balance, more sports specific research may be needed to clarify this transfer. No improvements were found in the overhead medicine ball throw, 20 m sprint and vertical jump height scores post both static and dynamic training. These results provide no support for the proposal of a more enhanced and efficient transfer of energy due to an enhanced core. Therefore we reject part of our hypothesis in that dynamic exercise will demonstrate a positive transfer of training effect to dynamic tasks. This is in agreement with Scibek and colleagues (Scibek et al., 2001) who looked at the effect of Swiss ball core stability training on subsequent swim performance. Their results showed enhanced core strength in static exercises
K.L. Parkhouse, N. Ball however no improvements in swim performance. Furthermore Nesser and colleagues (Nesser et al., 2008) showed no correlation of core strength to strength and power measures in collegiate athletes. This indicates that power performance may not be affected by core strength refuting previous claims. However core training has been shown to improve 5,000 m run times (Sato and Mokha, 2009) indicating that core training modalities may have a better transfer to more endurance based events in the resistance of fatigue and maintenance of posture (Brumitt, 2004). Stanton and colleagues (Stanton et al., 2004) showed no improvement in running economy, however did not include a timed measure for the run trials performed. These studies and the current study’s findings support the notion that core training emphasizes local muscle adaptation and core strength without concomitant improvements in power based physical performance. Although the outcomes appear clear, it must be highlighted that only 12 participants were used in the study. We suggest that any future studies in this area should include a much larger sample size to ensure sound reliability of results. Furthermore, the transfer of training effect of the dynamic core exercises to the dynamic movements may have required a longer duration training program or an increased frequency of sessions. Early phase adaptations including increased stability, neuromuscular activity and proprioceptor activity have been shown after 5 weeks of training doing abdominal and one lower back exercise per day (Cosio-Lima et al., 2003), however these improvements were shown mainly in neuromuscular changes opposed to strength changes as measured by isokinetic testing. Thus the neuromuscular control and co-ordination trained by core dynamic exercises may only improve muscular recruitment in the initial phases opposed to the transferring into an external measure. Thus the benefits of the core training program here for the dynamic exercise may not be transfer into performance measures but may potentially improve kinematic and kinetic measures. Alongside program duration the nature of the exercise used may be changed for athletes with free weight exercises using moderate levels of instability may be more suitable to maintain specificity (Behm et al., 2010). The concept of specificity suggests that quick, explosive dynamic performance variables are likely to be improved by similar type training actions. To train improved speed of force application more importance is placed on performing the exercise powerfully compared to the selection of the exercise movement (Behm and Sale, 1993). Although dynamic exercises were performed by the dynamic training group, explosive power and high rates of force development were not emphasized and subsequently not transferred over. A lower repetition range with emphasis on increased speed of movement whilst maintaining lumbo-pelvic stability may have seen a better transfer into the sprint, jump and throw tests as the core would be trained in a similar manner to its use within these tests. The loading measures used in this study may not have been sufficient to improve core muscle function during dynamic exercises. Hibbs and colleagues (Hibbs et al., 2008) suggested that the cores are trained more for everyday requirements (low loads, slow movements) opposed to an athlete requirement of high load and resistive movements. The population group in this study
Influence of dynamic versus static core exercises on performance in field based fitness tests indicated a better use of their core strength in static movements compared to the high force dynamic field tests. In summary, the results of this study suggest that 6 weeks of stability ball training doesn’t improve dynamic field based performance tests based on the sample size used. The benefits of core training may reside in long term athlete development programmes whereby appropriate posture and core strength may transfer into improved co-ordination and exercise performance. Increases in training duration and speed of movement in dynamic core exercises may provide a more specific stimulus of the core for transfer into dynamic field based movements, however this warrants further investigation.
Practical applications The current study shows that both static and dynamic core stability exercises trained over a 6-week period are able to effectively increase the core strength of participants. These strength benefits do not transfer into improved dynamic performance in sprinting, throwing and jumping. The study indicates that short term training may only improve core strength by reducing fatigue in the core musculature and allowing the athlete more neuromuscular control during balance. A program that incorporates both static and dynamic exercises may provide these benefits if the dynamic exercises are then performed with increased velocity. This may improve the transfer of training effect into dynamic performance. It must be understood that the findings may only be applicable to the population under investigation and the effects on elite athletes is unknown. However due to the assumed improved core strength and physicality of elite performers it can be assumed that their scope for adaptation is smaller than the current population and thus non-significant finding for core transfer into dynamic performance can be reasonably assumed. Findings do not discourage the use of core stability ball training; instead, they suggest that specificity on the rate of force development, speed and power of each core exercise may be needed to transfer into sporting performance.
Acknowledgements Sincere thanks to all the participants who devoted their time and effort to this study.
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