Eccentric Exercise

C H A P T E R

37 Eccentric Exercise: Benefits and Applications to Training Jonathan Mike Exercise Science Department, Grand Canyon University, College of Science, Engineering and Technology, Phoenix, AZ, United States

INTRODUCTION Dynamic muscular contractions can be characterized by two primary actions, concentric and eccentric contractions. A concentric contraction results in muscle shortening and occurs when the force produced during a contraction exceeds the force applied to the muscle. Alternatively, an eccentric contraction occurs when the muscle is forcibly lengthened or elongated. An eccentric contraction results when the force produced inside the muscle is less than what is applied to the muscle externally and results in active lengthening of the muscle fibers under some level of load. When directly compared, eccentric muscle actions are able to produce greater force, an amount estimated to be 20%–60% higher than concentric strength levels, and in the same respect, lower levels of neural activation have been shown in eccentric contractions than in concentric efforts. Owing to its specific physiological and mechanical properties, there is an increasing interest in using eccentric (ECC) muscle work for rehabilitation and clinical purposes. Nowadays, ECC muscle actions can be generated using various exercise modalities that target small or large muscle masses with minimal or no muscle damage or pain. Therefore if caution is taken to minimize the occurrence of muscle damage, ECC muscle exercise can be proposed not only to athletes and healthy subjects but also to individuals with moderately to severely limited exercise capacity, with the ultimate goal being to improve their functional capacity and quality of life. The use of eccentric muscle actions for the purpose of therapeutic exercise has gained greater acceptance in light of the growing evidence that positive adaptations can result without incurring excessive muscle damage. Older adults and individuals with chronic conditions often have limited exercise tolerance and may require specialized exercise programming provided by rehabilitation professionals. The ability to elicit muscle and neural adaptations to exercise in people within compromised metabolic and cardiovascular capacity makes eccentric exercise an intriguing training option. Rehabilitation interventions featuring eccentric exercise appear to have similar efficacy and safety to concentric training for the management of conditions such as coronary artery disease, musculoskeletal conditions such as tendinopathies and knee osteoarthritis (OA), as well as chronic neurodegenerative diseases such as Parkinson’s disease. Moreover, there is some evidence to suggest that the gradual introduction and progression of eccentric training loads result in large strength gains in older adults without incurring adverse changes in serum creatine kinase, tumor necrosis factor-α, or other clinical markers of muscle damage (LaStayo et al., 2003). This chapter examines the multitude of benefits with eccentric training and its applications and extends its benefits to a wide variety of general, athletic, and clinical populations.

BENEFITS OF ECCENTRIC TRAINING Incorporating eccentric training and programming into a resistance training program can facilitate numerous benefits that extend well beyond simple increases in strength and hypertrophy for populations ranging from athletes desiring peak performance to clinical patients involved in physical rehabilitation (Fig. 37.1). With eccentric exercise,

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FIGURE 37.1  Eccentrics 3-Dimensional.

greater force output is produced during a maximal eccentric action primarily because of the ability to use higher external loads. Research focusing on the effects of overload training (100%–120% 1-repetition maximum [1RM]) during the eccentric phase of a movement has routinely demonstrated a greater ability to develop maximal strength. Research by Doan et al. [1] reported that applying a supramaximal load (≥105% of 1RM) on the eccentric phase of the lift elicited increases in 1RM concentric strength by 5–15 lbs. These abilities to increase strength have been shown to be greater when compared to concentric resistance training using lighter loads [2–6]. In addition, a number of other adaptations have been reported in the literature in support of eccentric training and include heightened neural adaptations in response to eccentric training when compared to concentric training [4]. These neural adaptations likely include spinal and cortical mechanisms (i.e., larger excitability and greater involvement of brain areas) and are areas in need of greater research [7]. In addition, the energy cost of eccentric exercise is comparably low despite the high muscle force being generated. This makes eccentric training an appealing strategy for those wishing to gain additional strength and hypertrophy due to the fact that more volume of training can be performed without excessive fatigue. In a fascinating display, exercise-induced hypertrophy from eccentric exercise is likely manifested by greater muscular tension under load, which has been a situation that has been mechanistically explained to represent a reversal of the size principle of motor unit recruitment, resulting in fast-twitch motor units being preferentially recruited earlier in the process [8]. Finally, and as a mechanistic link to reports of greater hypertrophy, eccentric exercise is also linked to more robust increases in protein synthesis [9] as well as a larger rise in insulin-like growth factor-1 mRNA expression [8] when compared to concentric muscle actions. Scientific literature abounds which indicates that eccentric training sessions elicit greater muscle damage than concentric training as represented by a loss of force production and increases in soreness as well as increased concentrations of serum-based proteins of myofibrillar origin [10,11]. The response to damage from eccentric training is thought to be associated with a mechanical disturbance of the actomyosin bond vs. ATP-dependent detachment, leading to greater stress and strain on the contractile apparatus than other muscle actions, increasing the susceptibility to muscle damage [12]. Other interesting findings related to muscle damage include indications that the degree of eccentric-induced muscle damage is greater in the upper limb musculature than in the lower limb [13,14]. It also appears that fusiform muscles (i.e., biceps brachii) are more susceptible to eccentric-induced damage than penniform muscles (i.e., rectus femoris) due to pennate muscles having short fascicles that attach obliquely to a central tendon running the length of the muscle [13]. Finally, evidence also indicates that a fiber type–specific response to muscle damage may occur whereby type II muscle fibers appear to be more vulnerable to damage during eccentric exercise than type I muscle fibers [15,16]. Whether or not these intramuscular factors will eventually result in altered eccentric prescriptions primarily in clinical populations to avoid (or promote) damage and its ensuing repair and remodeling phase’s remains to be seen, but the scientific foundation is present for such considerations to be entertained. As mentioned previously, incorporating eccentric training not only benefits healthy adults and athletic populations but these benefits also extend to a number of clinical populations. For example, the aging process results in a progressive and continual reduction in muscle strength. For this reason alone, incorporation of eccentric training could be considered in an elderly population for its known ability to improve muscle strength and power while also reducing their risk for falls and potential fracture risk [17,18]. With respect to increases in power, eccentric exercise training serves an important part in all aspects of sports and is critical during the strength-shortening cycle [19] and

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has been shown to be an effective modality in increasing (explosive) muscle strength and muscle cross-sectional area, leading to increased sarcomere length. Recent evidence suggests that eccentric and overspeed training modalities are effective in improving components of muscular power and that eccentric training induces specific training adaptations relating to muscular force. It was found that eccentric training with overspeed stimuli was more effective than traditional resistance training in increasing peak power in the countermovement jump [20]. Other clinical populations can benefit from incorporating eccentric training, particularly if the patient exhibits a low level of strength and is just beginning a resistance training or rehabilitation program. For example, research involving stroke and chronic obstructive pulmonary disease (COPD) patients has demonstrated a significant preservation of eccentric strength when compared to age-matched healthy controls [21,22]. Additionally, increases in collagen synthesis and improvements in overall bodily function [23] regularly occur as part of a comprehensive rehabilitation program. Physical rehabilitation populations can also derive benefits from eccentric training, starting first with the known cross-education effect or the transfer of strength gains unilaterally from one limb/side to the other [24]. Protocols using cross education have been shown to successfully improve quadriceps strength in the limbs of healthy, uninjured participants, although the exact mechanism is still not fully explained. Recent evidence examined the effect of eccentric exercise on quadriceps strength and activation gains in the unexercised limb. Eighteen healthy individuals were randomly assigned to an eccentric training group or a control group. Quadriceps strength and activation were measured before, at the middle of, and after intervention. Eccentric training participants exercised their dominant limb with a dynamometer in eccentric mode at 60 degrees/s, 3 times per week for 8 weeks, and found greater eccentric strength in the unexercised limb between trials. It was concluded that exercising with eccentric actions resulted in mode-specific and velocity-specific improvements in quadriceps strength in the unexercised limb, suggesting that strength gains may have occurred because of enhanced neural activity [25].

ECCENTRIC APPLICATION AND PROGRAM DESIGN A variety of eccentric training techniques are available along with the use of a number of nontraditional exercises for able-bodied, clinical, as well as athletic populations. While several eccentric techniques exist in which strength and conditioning (S&C) and fitness professionals can be used, four categories of eccentric techniques are most commonly used. These four techniques are highlighted in the following section:

2/1 Technique The 2/1 technique for emphasizing the eccentric component involves lifting the weight through its concentric range of motion with two limbs, while moving the weight back through the eccentric phase with one limb. It should be emphasized that the load should be heavy enough to pull through the concentric phase as quick as possible but heavy enough to challenge the individual throughout the eccentric portion. Specifically the load during the eccentric phase should be twice as high as during the concentric phase, and an approximate load of 70% of bilateral concentric 1RM is considered to be a general starting point. Sets of three to five reps per limb are performed (6 to 10 total reps per set), with a rest interval of 60 s. Tables 37.1 and 37.2 provide examples of several exercises that can be modified to accentuate the eccentric phase using any of the techniques highlighted throughout this manuscript. Finally, past experiences of using this technique indicate that a wide variety of populations can benefit from its use.

Two-Movement Technique The two-movement technique is slightly more technical than the 2/1 eccentric technique. With the two-movement technique, it is recommended that the concentric portion should be a compound (multijoint) exercise coupled with an isolation exercise for the eccentric portion of the lift. It is our contention through personal experience and coaching that this technique should be practiced among more highly trained individuals. The volume and load parameters should consist of 90%–110% of your maximal load while incorporating four to five sets of five repetitions with an eccentric duration of 5 s. Rest periods should be 1 to 2 min in between sets. Sample exercises using this technique (i.e., power clean/reverse curl, close-grip bench/triceps extension, etc.) and basic prescription recommendations are provided in Table 37.2.

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TABLE 37.1  Eccentric-Emphasized Exercises—Upper and Lower Body Exercise

Eccentric Duration Emphasis

Sets and Reps

Suggested Eccentric Technique

Suspension trainer (TRX) row

3–5 s

Upper body

3–5 sets × 6–8 reps

2/1; Superslow

Pull-ups

3–5 s

Upper body. Can focus on eccentric- 3–5 sets × 8–10 reps with only training or perform concentric concentric; 3–5 sets × 6–8 with eccentric emphasis reps with eccentric-only training

Superslow Can use heavier loading and decrease eccentric duration (i.e., 85% 1RM for 4 s) Bodyweight and strength dependent

Glute-ham raise

3–5 s

Lower body. Focus on eccentriconly training or perform normal concentric reps with eccentric emphasis with prescribed duration

Slow Bodyweight and strength dependent. Can also use plates or bands

Manually glute-ham raise

3–5 s

Lower body. Can focus on eccentric- 3–5 sets × 10–12 reps only training with eccentric-only Requires a partner training

Single-leg Romanian deadlift or good mornings. (barbell or dumbbell)

3–5 s

Lower body. Can focus on eccentriconly training or perform normal concentric reps with eccentric emphasis with prescribed duration

3–5 sets × 8–10 reps with Two-movements technique concentric; 3–5 sets × 10– 12 reps with eccentriconly training

Glute bridge and hip 3–5 s thrust (body weight, plates, or barbell) Can also perform single-leg movements

Lower body. Can focus on eccentriconly training or perform normal concentric reps with eccentric emphasis with prescribed duration

3–5 sets × 8–10 reps with concentric; 3–5 sets × 6–8 reps with eccentric-only training

Half-kneel-bottom-up 3–5 s press-eccentric-only training

Upper body. Mainly focused on 3–5 sets × 6–8 reps eccentric-only training while also incorporating half-kneeling position and additional core and hip stability Can be used for concentric portion and eccentrically emphasized or eccentric-only training

3–5 sets × 8–10 reps with concentric; 3–5 sets ×  10–12 reps with eccentric-only training

Supramax; Slow Supramax was chosen for this exercise because of the overall difficulty Bodyweight and strength dependent. Can also use plates or bands

Supramax; Slow Plates or loaded barbell can be used for supramax in addition to slow techniques 2/1 Technique; Slow; Supramax Can be used as a mix of all

Slow/Superslow This technique is relatively simple. The lifter executes an exaggerated, slow-speed eccentric phase while concentrically lifting the bar explosively. This is perhaps one of the more common eccentrically emphasized techniques than the other techniques, and as a result, it has been used to a greater extent. Again we have attempted to provide details in Table 37.2 with regard to this technique. It should be emphasized that the eccentric duration varies depending on the load used. For example, a lower % 1RM yields a longer eccentric duration (i.e., 60% 10–12 s), whereas a heavier load (i.e., 85%) would likely yield approximately 4-s eccentric action duration. A load ranging from 60% to 85% 1RM is commonly used, with eccentric action durations ranging from 2 to 15 s, depending on the load assignment, type of movement, size of muscle group, etc. A rest period of 60 s is commonly used that could be further modified depending on other details found within the overall exercise prescription.

Negative (Supramax) This type of training primarily refers to the eccentric action and is mainly used as an eccentrically emphasized training technique. Although an effective technique, one drawback is that it requires at least one spotter, and depending on the exercise, load, and number of eccentric repetitions to be completed, two or three spotters may be needed. For example, when performing a bench press, one to two spotters are recommended. There should be no actual

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Practical Scenarios

TABLE 37.2  Eccentric Training Techniques Technique

How to Perform

Eccentric Duration

2/1 Technique

• Lift the weight concentrically 5 s using two limbs (both arms for an upper-body exercise, both legs for a lower-body exercise) • Return the weight eccentrically with one limb

Sets and Reps

Example Exercises

• 70%–80% 1RM of your selected exercises • 60 s rest

• Rowing, various biceps and triceps exercises that can be done using the triceps rope, dumbbells, free weight and machines • See Table 37.1

4–5 sets × 5 90%–110% 1RM of the weight typically used for your selected exercises For example, use 90%–110% 1RM of your reverse curl or triceps extension. 60-s rest

Power clean/reverse curl, close-grip bench/triceps extension, DB bench/flies, DB squat/single-leg DB squat

Two-movement Use a compound movement technique (i.e., bench press; power clean) and the eccentric portion of an isolation movement

5 s

Slow/ Superslow

Execute a superslow eccentric phase while concentrically lifting the bar explosively

Varies depending on 60%–85% of your max. 60-s rest the load Lower % 1RM yields a longer eccentric duration (i.e., 60% 10–12 s)

Various single-arm and single-leg exercises (i.e., triceps pushdowns, dumbbell split squat

Negative (Supramax)

Performing the eccentric-only portion of an exercise *Requires a spotter

The eccentric action is load dependent

Close-grip bench, bicep curls

Set of 1 rep. 110% and 130% of your maximum 8–10 s if the load is 110%–120% 4–6 s or 6–8 s if the load is 120%–130%

concentric lift with this type of technique, which commonly results in the spotter concentrically lifting the bar to the starting position after the lifter performs the eccentric rep. Therefore the lifter should focus their efforts on eccentric control throughout the supramaximal technique. As indicated in Table 37.2, sets of one repetition should be used with 110%–130% of concentric 1RM. However, the time of the eccentric action is load dependent with 110% and 130% of your maximum. For example, an 8- to 10-s eccentric action can be expected if the load is 110%–120% concentric 1RM. Furthermore, the lifter may increase the load percentage (125%–130% concentric 1RM) which will decrease the overall duration of the eccentric phase to somewhere around 4 to 5 s in duration. When performing this specific technique, it is recommended that three to ten sets of singular repetitions be completed at a load of 110%–120% 1RM. We recommend starting conservatively with this technique as it places a large demand on the nervous system and therefore can elicit rapid periods of overreaching and potentially overtraining. As a result, the individual should take a longer rest interval when using this technique and closely evaluate recovery, soreness, etc. before completing a subsequent workout using this technique. Provided that a muscle is not fully fatigued during concentric training [26], the use of heavy negatives (supramax) may elicit greater motor unit fatigue and thus provide an additional hypertrophic stimulus. The greatest improvements using supramaximal eccentric training (110%–120% 1RM) have been reported by Brandenburg and Docherty [27] who reported an increase in elbow extensor strength of 24% compared with 15% using standard resistance training after 10 weeks of training 2–3 times per week. Similar results were also reported by Doan et al. [1] who applied a supramaximal load (≥105% of 1RM) on the eccentric phase of the lift and elicited increases in 1RM concentric strength.

PRACTICAL SCENARIOS The following section is included in the hopes that it will help facilitate a broader understanding of how eccentric techniques can be used and hopefully stimulate additional thought by the reader to further apply the different eccentric techniques. Both scenarios are intended to build on the information outlined in Tables 37.1 and 37.2.

Practical Scenario 1 A 250-lb football player has a severe hamstring strain. To facilitate recovery and strength, it is recommended that the individual incorporates eccentric training into his program. His goals are to restore range of motion and strength

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and to use specific hamstring exercises to assist in this process. Once the initial inflammation phase has been resolved (i.e., 1–4 weeks), he can begin to primarily use open kinetic chain and non–weight-bearing exercises. Comfort and Matthews [28] have suggested to implement low-velocity eccentric activities such as stiff-legged deadlifts, eccentric hamstring lowering exercises, and split squats once the athlete has tolerated the non–weight-bearing exercises. Based on the recommendations from Comfort and Matthews [28], the next phase involves higher velocity eccentric exercises that include plyometric and sport-specific activities designed to increase hamstring torque and lower extremity power. Examples include squat jumps, split jumps, bounding, and depth jumps. Finally, sports-related progressions should complete the program. Comfort and Matthews [28] suggest progressing from unidirectional linear movements to bidirectional and then multidirectional movements. These examples may include progressions from twoleg jumps, single-leg hops, single-leg bounding, backward skips, lateral hops, lateral bounding, and zigzag hops and bounding. Furthermore, evidence from the study by Brughelli and Cronin [29] proposes that incorporating eccentric exercise for reducing the frequency of hamstring strains should include the following: high-force, maximal muscle elongation, high-velocity, multijoint movements, closed-chain exercises, and unilateral exercises. These include eccentric lunge drops, eccentric single and double leg deadlifts, and even a split stance “good morning” exercise with the load positioned in front compared to a posterior load on the back. It should be noted that we have provided similar eccentric-emphasized exercises for the lower body (Table 37.1) which can also be used in this scenario, for example, the specific eccentric action duration with the recommended set and rep scheme.

Practical Scenario 2 An advanced 28-year-old female lifter with 10 years of training experience would like to incorporate some eccentric-emphasized training into her training program to assist in further development of strength and hypertrophy. She has competed in strength sports throughout high school and college and continues to compete recreationally for the past 6 years while recently completing three bodybuilding competitions in the past 2 years. With this scenario, multiple eccentric-focused resistance training techniques can be used with exercises available in most commercial gyms. 2/1 Technique The 2/1 technique is an ideal eccentric technique for this type of scenario. For example, using bilateral machines (i.e., leg press or chest press) while raising the load with both limbs and lowering with only one limb will limit fatigue and allow the lifter to complete more eccentric actions. Both of these examples can also be completed with dumbbells, but care and caution need to be paid toward muscular failure with weights overhead. Additionally, eccentric one-arm pushups can be completed using the 2/1 technique by pressing up with both arms and lowering with one arm. Cluster Sets With Eccentric Emphasis Cluster sets involve of a series of repetitions interspersed by a very short (i.e., 5–30 s) rest interval [30]. A wellknown modern-day example of this training style is a “rest–pause” set. A partner or spotter helps raise the weight to the starting position. From here the lifter begins each series of repetitions with an eccentric action and completes the set (after concentric failure or as the last rep performed) with an eccentric action to a safe stopping point. With the technique the lifter can accumulate additional eccentric actions over the course of a multiseries cluster set. Forced Eccentric Training (Supramaximal Technique) These are primarily completed in a fatigued state with lighter loads. For example, as one reaches concentric failure at the end of a drop set, the spotter helps lift the weight and provides an additional load during the eccentric portion so that the eccentric tempo is relatively normal or even slower. In current bodybuilding culture, this is often referred to as “isotension,” in which isometric contractions are performed with additional tension provided by a spotter.

CLINICAL APPLICATION OF ECCENTRIC TRAINING Dynamic muscular contractions can be characterized by two primary actions, concentric and eccentric contractions. A concentric contraction results in muscle shortening and occurs when the force produced during a contraction exceeds the force applied to the muscle. Alternatively an eccentric contraction occurs when the muscle is forcibly lengthened or elongated. An eccentric contraction results when the force produced inside the muscle is less than what is applied to the muscle externally [31] and results in active lengthening of the muscle fibers under some level 5.  MINERALS AND SUPPLEMENTS IN MUSCLE BUILDING

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of load. Eccentric training is mainly incorporated in an indirect manner by S&C and fitness professionals; as a result, it is often underused and undervalued. Many discuss the aspect of eccentric training for its application to strength training and conditioning. While this segment certainly benefits from eccentric training, its application extends heavily in the clinical populations as well. The purpose of this chapter is to address both the implications and clinical applications of eccentric training, how eccentric training affects the outcomes within various clinical populations, general exercise guidelines, and it discusses future directions within eccentric training and clinical populations.

CLINICAL BENEFITS OF ECCENTRIC TRAINING Owing to sarcopenia and age-related muscle loss, research indicates that muscle mass and strength decrease approximately 10% per decade after the age of 50 [32–35]. Incorporating eccentric training and programming into a resistance training program can facilitate numerous benefits that extend well beyond simple increases in strength and hypertrophy for populations ranging from athletes desiring peak performance to clinical patients involved in physical rehabilitation. Eccentric exercise is generally considered a highly effective mode of conditioning for strength and hypertrophy but also extends these benefits to various clinical populations. For example, research by LaStayo et al. [36] demonstrated that eccentric exercise has successfully been explored in cancer survivors, in adults with metabolic disorders such as diabetes type 2, for neurological conditions such as Parkinson’s disease in adults and cerebral palsy in children, and for rehabilitation after knee surgery, in particular, replacement surgery for anterior cruciate ligament (ACL) as well as knee arthroplasty. In addition, the energy cost of eccentric exercise is comparably low despite the high muscle force being generated. The authors contend that the major defining properties of eccentric muscle contractions, the high force-generating capacity of the muscle, and low energy cost make eccentric training an appealing strategy and represent a unique training environment and effective countermeasure for muscle wasting in many clinical populations in which muscle atrophy is of concern. Furthermore, the aging process results in a progressive and continual reduction in muscle strength. For this reason alone, incorporation of eccentric training can be considered in an elderly population for its known ability to improve muscle strength and power while also reducing their risk for falls and potential fracture risk [17,18]. In addition, those within the clinical populations can benefit from incorporating eccentric training, particularly if the patient exhibits a low level of strength and is just beginning a resistance training or rehabilitation program. For example, research involving patients with stroke and COPD has demonstrated a significant preservation of eccentric strength when compared with age-matched healthy controls [21,22]. Eccentric training is also associated with the known cross-education effect or the transfer of strength gains unilaterally from one limb/side to the other. Recent evidence reported that protocols using cross education have been shown to successfully improve quadriceps strength in the limbs of healthy uninjured participants [25], although the exact mechanism has not been fully elucidated.

ECCENTRIC EXERCISE AND CLINICAL OUTCOMES S&C and fitness professionals often have to develop resistance training programs to accommodate clients and athletes who may possess certain clinical conditions that need attention through eccentric exercise. Eccentric loads can be appropriately dosed and increased over time as eccentric exercise training can be used safely and effectively in rehabilitation of serious medical conditions and clinical applications. Therefore this section will highlight a variety of clinical and rehabilitation circumstances in which eccentric training has a favorable impact and effective treatment strategy.

TENDINOPATHIES Multiple studies have shown eccentric exercise to be very promising as a potential nonoperative and effective training modality for tendinopathies. Although ‘‘tendonitis’’ is often used as a general term for tendon injuries, early work by Leadbetter [37] previously defined tendonitis as a symptomatic degeneration of a tendon with vascular disruption and inflammatory repair. However, more recently, the term ‘‘tendinopathy’’ has been used as an all-encompassing term for tendon injuries. Over the past decade, eccentric training has been effectively used as a treatment for tendinopathies. The very first study by Alfredson [38] investigated eccentric exercise on diseased tendons, and the protocol used in that study has been used in most studies on eccentric training. In his original report,

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15 athletes with chronic Achilles tendinosis performed three sets of 15 repetitions of bent knee and straight knee calf raises, twice a day, 7 days per week over 12 weeks. Subjects were told to work through pain, only ceasing exercise if pain became disabling. The load was increased in 5-kg increments with the use of a backpack that carried the weight once carrying the weight was pain free. Researchers found that all 15 patients returned to preinjury levels of activity. Additionally, they had a significant decrease in pain with a significant increase in strength. Similar results by Shalabi et al. [39] also found that eccentric training resulted in decreased tendon volume and decreased intratendinous signal, which correlated to improved clinical outcomes, in soccer players [40]. For a training application, in general, load and volume should be progressed gradually and should be dictated by the amount of pain the client or athlete experiences. Owing to the incidence of injury and emphasis on recovery, it is advised that load used not be determined by a 1RM.

ELDERLY POPULATION Considering that eccentric work requires muscles to contract eccentrically with little demand for energy, yet can overload muscle to a greater extent, it has been used as an effective strategy for elderly exercise-intolerant individuals and those at risk for falling. LaStayo et al. [17] found greater strength increases after eccentric training that resulted in improved balance, stair descent, and fall risk only in the eccentric group. It should be noted that the significant increases in strength in eccentric training groups in the elderly population seems to be linked to an equal magnitude increase in fiber cross-sectional area [17]. Although research supports the use of eccentric training in the elderly population, the reversal of the size principle is a suggested phenomenon during eccentric muscle actions that may be advantageous for this population, considering one can produce greater force in amounts estimated to be 20%–60% greater than force levels generated during concentric activities. During these contractions, type II motor units are called into play to contribute to force output; thus the heavier the load is during eccentric activity, the more likely the type II fibers are recruited to enhance force generation. The use of heavier eccentric loading is an appealing strategy to help combat the age-related muscle loss often accompanied by the elderly and loss of type II fibers. However, the value of eccentric exercise has often been questioned considering that those individuals unaccustomed to this type of exercise can likely experience muscle soreness and muscle damage. This is of particular concern in the elderly population or in patients with neuromuscular disease. However, many believe that the response to damage may be overstated. Nonetheless, recently, Lovering and Brooks [41] concluded that exercise (including eccentric components) is generally recommended; however, there are currently no common recommendations for all individuals, and guidelines for eccentric exercise are still lacking.

OSTEOPENIA It has been suggested that eccentric training, due to its high force production, also has an impact on bone during resistance training and should also yield increases in bone adaptation [42–44]. Hawkins et al. [44] found that after 18 weeks of maximal effort, eccentric exercise on one leg and concentric exercise on the other leg (using a leg dynamometer), twelve 20- to 23-year-old women significantly increased mid-femur bone mineral density by 3.9% after the eccentric training (a nonsignificant increase of 1.1% was noted in the concentrically trained leg). This finding suggests that eccentric training to leg muscles elicits a greater osteogenic stimulus than concentric resistance training. Taken together, it suggests that the greater eccentric peak forces produced from the eccentric group were the stimulus for this bone response as the total resistance work over the 18-week period was equivalent to that of the concentric training group. Although these results show a positive response on bone from eccentric training, additional investigation into the osteogenic effects and potential outcomes of eccentric training is needed.

ECCENTRIC TRAINING GUIDELINES Although the clinical benefits of eccentric training extend beyond what has been discussed in the previous sections, it is important for the personal trainer and fitness professional to apply eccentric training guidelines to any potential clients they may encounter who experience any number of the clinical conditions outlined. Suggested

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Sidebar Practical Applications

TABLE 37.3 Sample Progression of Total Volume of Eccentric Work on Eccentric Ergometer Over 12 Weeks Exposure-Adaptation Phase (1–2 weeks)

Progressive Eccentric Work Phase (3–12 weeks)

Frequency

2–3 times/week

2–3 times/week

Duration *Duration may be substituted with sets and repetitions of different eccentric movements.

5–8 min/session

10–12 min/session (weeks 3–4) 14–16 min/session (weeks 5–6) 18–20 min/session (weeks 7–12)

Intensity

Very light

Fairly light (weeks 3–5) Moderately hard (weeks 6–12)

Adapted from LaStayo P, Marcus RL, Dibble L, Frajacomo F, Lindstedt SL. Eccentric exercise in rehabilitation: safety, feasibility and application. J Appl Physiol (1985) 2013. *The eccentric exercise duration should be performed for up to 20–30 min/session, two to three times/week for 6–12 weeks.

progressions and guidelines are provided depending on the training background and abilities of clients. LaStayo et al. [36] suggest the following: An eccentric exposure-adaptation phase must be used initially to avoid unnecessary muscle damage. Therefore this phase better prepares the muscle to experience the higher forces that often accompany the progressive eccentric negative work phase (Table 37.3). In general, the expectation is that the loading goal during the progressive eccentric work phase should exceed an isometric maximum load, and the eccentric exercise duration should be performed for up to 20–30 min/session, two to three times/week for 6–12 weeks. During the progression and incorporation of eccentric work, the goal for the personal trainer and fitness professional for the rehabilitating participant to resist progressively a higher load for prolonged periods. Specifically, the exercise load being resisted should surpass the participant’s isometric maximum load (i.e., the load should now exceed that which can be moved concentrically). Eccentric exercise can be implemented with traditional resistance exercise equipment or with the use of body mass alone. In addition, functional weight-bearing activities, such as moving from standing to sitting, can be used as an eccentric activity.

CONCLUSION AND FUTURE DIRECTIONS Eccentric actions are a distinct phase of nearly every muscular contraction that is represented by a combination of several unique factors, which ultimately impacts how the involved musculature responds. A number of eccentric training strategies exist which can allow for a wide variety of applications across nearly all populations. Although eccentrically dominated movements may not be needed in all situations, it is our contention that nearly all populations can indeed derive benefit. Toward this aim, the approach taken throughout this chapter was to highlight a number of different eccentric strategies along with examples and potential prescriptive scenarios upon implementation to encourage the reader to incorporate and explore other means in which eccentric can be incorporated into their athletes or client’s programs. From this article, we hope to better highlight many ways how eccentric training can be incorporated into the training and therapy programs of active, athletic, and clinical populations. From a clinical perspective, in terms of eccentric exercise and its acute and chronic effects on healthy and diseased tendons, some evidence does suggest eccentric training as a first line of treatment for these conditions, in addition to other clinical conditions highlighted. The S&C coach, personal trainer, and fitness professional should assess each client individually to potentially incorporate and even explore the use of eccentric training into a client’s therapy and rehabilitation program. However, knowledge of the adaptations of the neuromuscular system to eccentric stress remains incomplete.

SIDEBAR PRACTICAL APPLICATIONS The following side bar represents eccentric training perspectives and overall highlights previous scientific research outlined in this chapter: You mention that all populations might derive some benefit from eccentric training. What do you think are the main drivers of this benefit? Is it the potential for training variety? The main drivers of eccentric training serve multiple purposes. In addition to training variety, it serves to promote excellent results to strength and hypertrophy, not only for both the trainee, athlete, and S&C coaches but extends its applications and benefits for clinical patients involved in physical rehabilitation. Numerous adaptations have been reported in the literature in support of eccentric training and include heightened neural adaptations in response to eccentric training when compared with concentric training (i.e., spinal and cortical mechanisms; larger 5.  MINERALS AND SUPPLEMENTS IN MUSCLE BUILDING

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excitability and greater involvement of brain areas). In addition, the energy cost of eccentric exercise is comparably low despite the high muscle force being generated. This adaptation alone is a very appealing strategy for those wishing to gain additional strength and hypertrophy because of the fact that more volume can be performed without excessive fatigue. Are there any specific populations who you think would be particularly recommended to use eccentric training? If so, why? Actually, all populations, including general population, athletes, and clinical populations can indeed derive benefit. However, there are no benefits that are strictly specific to one population over the other. Rather, the recommend use of eccentric training covers all subsets of populations. For example, because aging results in sarcopenia and age-related muscle loss, incorporating eccentric training is highly recommended as the ability to use higher external loads during the eccentric phase of a movement would enhance maximal strength. Considering eccentric training is known for their ability to improve muscle strength and power, it would also reduce their risk for falls and potential fracture risk (a common trait seen within the elderly populations). Eccentric training is also associated with the known cross-education effect or the transfer of strength gains unilaterally from one limb/side to the other. Evidence reported that protocols using cross education have been shown to successfully improve quadriceps strength in the limbs of healthy uninjured participants, although the exact mechanism has not been fully elucidated. With respect to S&C and power output, eccentric exercise training serves an important and critical role during the stretch-shortening cycle and has been shown to be an effective modality in increasing (explosive) muscle strength and muscle crosssectional area, leading to increased sarcomere length (although controversial). Most of us just discuss the aspect of eccentric training for its application to strength training and conditioning and the athletic and clinical population. However, it is further documented that eccentric exercise has successfully been explored in cancer survivors, in adults with metabolic disorders such as diabetes type 2, for neurological conditions such as Parkinson’s disease in adults and cerebral palsy in children, and for rehabilitation after knee surgery, in particular, replacement surgery for ACL as well as knee arthroplasty. In terms of eccentric exercise and its acute and chronic effects on healthy and diseased tendons, some evidence does suggest eccentric training as a first line of treatment for these conditions. Finally, the possibility for using eccentric training and eccentric training modalities for NASA astronauts in space remains to be seen but is likely to transcend because of its effectiveness of adding and maintaining strength, muscle mass, and functional strength, which is critical for space exploration. There is some evidence for task specificity in respect of muscle action. With that in mind, do you think that certain types of athletes will therefore benefit more from eccentric training than others? To preface this, four of the most undervalued and overlooked training methods for athletes are deceleration, isometrics, aerobic development, and eccentric training. With that said, and because we are discussing eccentric training, all types of athletes will benefit from eccentric training. However, those athletes who may participate in high-velocity sports and who use change of direction (which are most sports) should be incorporating eccentric training into their program. For example, those recovering from a hamstring strain or ACL tear most certainly want to use eccentric training in their recovery, for added strength. How does this apply to athletes who may or may not be injured? With eccentric training, muscle absorbs energy developed by an external load. So, during an eccentric muscle action, the shock absorber spring component of the muscle tendon system contributes energy to the forces produced. This is particularly important during a variety of sporting movements such as downhill walking/running, landing mechanics, alpine skiing, countermovement jumps, sprinting, drop jumps, and long and high jumping, all of which require posterior chain strength and degrees of deceleration as many injuries occur during deceleration or change of direction. Therefore incorporating eccentric training is definitely worth doing to reduce injury risk and injury prevention within sports. Eccentric training is often associated with a greater risk of delayed-onset muscular soreness (DOMS). Based on this, would you suggest a lower training frequency when incorporating eccentric exercises? Similarly, would that mean eccentric training was better suited to a body part split than a full-body routine? It really all depends on how your current training program is set up to begin with and whether or not you need a lower training frequency when using eccentric training. If you train with minimal eccentric emphasis, then add an eccentric-emphasized exercise/or eccentric duration to an exercise, you may experience some DOMS the next day or two. However, it is highly dependent on the overall volume used. For example, focusing on the eccentric portion during pull-ups for four sets of eight, with an eccentric duration of 3–4 s, is no easy feat and can be challenging for many vs. eccentric training on the last set or two. The same concept applies to any other exercise. There has been only one study to date which used a total-body workout that each exercise was eccentrically emphasized. While performing full-body session with an eccentric emphasis (1-s concentric and 3-s eccentric on all exercises), elevated resting energy expenditure (REE) increased approximately 9% after workout and up to 72 h. However, the REE was likely caused by recovery and repair factors linked with DOMS, muscle repair process, and the energy costs associated

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with protein synthesis. With that said, it is best to experiment with both body part splits and full-body workouts. But on the whole, and although eccentric training produces more DOMS, I do not think you need to lower your training frequency when doing eccentric training, unless your entire workout is heavily eccentric based for all exercises; then the recovery becomes an issue. Do you think there are any specific recovery modalities that would help speed recover from eccentric training workouts? To date, there are no specific recovery modalities that would help speed recovery from eccentric training workouts. However, various recovery modalities have been addressed and are recommended from the literature which a wealth of trainers, coaches, and lifters use. These included protein supplementation, creatine supplementation, contrast showers, massage, foam rolling, quality sleep, leucine supplementation, cold-water immersion, and some antioxidants. In addition, tracking recovery and the use of software programs has also become more popular including Omegawave, BioForce, rating of perceived exertion, and heart rate variability. There is also the use of specific recovery questionnaires that can be used to monitor recovery for athletes. You note that eccentric training may cause more exercise induced muscle damage (EIMD) in (1) upper body muscles, (2) fusiform muscles, and (3) type II muscle fiber areas. Do you interpret these findings to mean that eccentric training may lead to greater adaptations in these cases or, contrarily, that the higher EIMD risk may outweigh the potential benefits? From the available science, eccentric training does seem to affect the upper body musculature more than lower body. Fusiform muscles (i.e., biceps) having short fascicles that attach obliquely to a central tendon running the length of the muscle are more susceptible to damage, along with a fiber type–specific response to damage as well. It is difficult to say if these will or can lead to greater adaptations mainly due to interindividual variability in skeletal muscle fiber types among lifters and athletes, differences in sports, training methods, and morphological differences, and responses to muscle damage. With respect to muscle damage, that is just one main contributing factor that helps facilitate muscle hypertrophy, along with time under tension, and metabolic stress. However, there are those who may be high responders to muscle damage, low responders, and no responders, which can impact responses to eccentric activity. It goes back to my previous statement that it all depends on how much volume of training you do and whether or not eccentric training encompasses a large portion of your training. For the overwhelming majority of athletes and lifters, it does not, at least not purposely. Do you really think there is a true reversal of the size principle occurring during eccentric muscle actions? Considering the increased strength and hypertrophy responses from eccentric training and the fact you can produce greater force in amounts estimated to be 20%–60% greater than force levels generated during concentric activities, it is highly likely (to an extent) there is a true reversal of the size principle during eccentric muscle actions. Although the overall evidence is fairly limited right now, the current evidence does suggest this phenomenon. As an example, one of the various training technique used for eccentric training is supramaximal training (i.e., 115%–125% 1RM). During these contraction, type 2 motor units are called into play to contribute to force output, thus the heavier the load is during eccentric activity, the more likely the type II fibers are recruited to enhance force generation. However, although you may not completely recruit all type II fibers simultaneously, type II fibers are being recruited more. Of course, genetics and training do play a role as well. Do you have any other practical tips for incorporating eccentric training? As far as practical tips for incorporating eccentric training are considered, if you are highly trained, then you can do a little more volume for eccentric training. Remember the energy cost is less compared to concentric work, so you can do more volume without accumulative fatigue. Second, if you are new(er) to eccentric activity, start conservative and begin with a single-joint exercise, then progress to multijoint movement such as Romanian deadlift (RDL), glute-ham raise, single-leg exercises, etc. You will likely find that some exercises elicit more damage or soreness than others, so you will have to experiment. Third, some of the eccentric training techniques required additional spotters (i.e., supramaximal technique), so this may impede training time or athletes training time if multiple spotters are needed. Fourth, for a given exercise that is eccentrically emphasized (i.e., 3–5 s duration for multiple sets and reps), stick with this for 3–4 weeks or rotate out with a normal cadence, and you will find that the transferability is very high. Yes, you are doing more overall “work” for eccentric training, but the payoff is even bigger when you return to the same exercise but with a normal contraction rhythm. Do you also see a role for concentric-only training in any circumstances? The role of concentric-only training does have benefits. In terms of training, there are numerous applications in which concentric-only training is helpful, especially for in-season play in which the maintenance of speed and power is critical. These included prowler pushes, sled drags, medicine balls throws, and various strongman events including farmers walk and yoke walk, in which the eccentric portion is very limited. There are also applications to

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squats such as concentric-only squat (i.e., Anderson squats) and various upper- and lower-body movements. These concentric-only training approaches can be used to address weak points in one’s training, add variety, and limit damage/soreness.

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[35] Skelton DA, Greig CA, Davies JM, Young A. Strength, power and related functional ability of healthy people aged 65-89 years. Age Ageing 1994;23:371–7. [36] LaStayo P, Marcus RL, Dibble L, Frajacomo F, Lindstedt SL. Eccentric exercise in rehabilitation: safety, feasibility and application. J Appl Physiol 2013;116:1426–34. [37] Leadbetter WB. Cell-matrix response in tendon injury. Clin Sports Med 1992;11:533–78. [38] Alfredson H, Pietila T, Jonsson P, Lorentzon R. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med 1998;26:360–6. [39] Shalabi A, Kristoffersen-Wilberg M, Svensson L, Aspelin P, Movin T. Eccentric training of the gastrocnemius-soleus complex in chronic Achilles tendinopathy results in decreased tendon volume and intratendinous signal as evaluated by MRI. Am J Sports Med 2004;32:1286–96. [40] Langberg H, Ellingsgaard H, Madsen T, Jansson J, Magnusson SP, Aagaard P, Kjaer M. Eccentric rehabilitation exercise increases peritendinous type I collagen synthesis in humans with Achilles tendinosis. Scand J Med Sci Sports 2007;17:61–6. [41] Lovering RM, Brooks SV. Eccentric exercise in aging and diseased skeletal muscle: good or bad? J Appl Physiol (1985) 2014;116:1439–45. [42] Nickols-Richardson SM, Miller LE, Wootten DF, Ramp WK, Herbert WG. Concentric and eccentric isokinetic resistance training similarly increases muscular strength, fat-free soft tissue mass, and specific bone mineral measurements in young women. Osteoporos Int 2007;18:789–96. [43] Alfredson H, Nordstrom P, Pietila T, Lorentzon R. Bone mass in the calcaneus after heavy loaded eccentric calf-muscle training in recreational athletes with chronic achilles tendinosis. Calcif Tissue Int 1999;64:450–5. [44] Hawkins SA, Schroeder ET, Wiswell RA, Jaque SV, Marcell TJ, Costa K. Eccentric muscle action increases site-specific osteogenic response. Med Sci Sports Exerc 1999;31:1287–92.

Further Reading [1] Burd NA, West DW, Staples AW, Atherton PJ, Baker JM, Moore DR, Holwerda AM, Parise G, Rennie MJ, Baker SK, Phillips SM. Low-load high volume resistance exercise stimulates muscle protein synthesis more than high-load low volume resistance exercise in young men. PLoS One 2010;5:e12033. [2] Carothers KC, Kyle F, Alvar BA, Dodd DJ, Johanson JC, Kincade BJ, Kelly SB. Comparison of muscular strength gains utilizing eccentric, standard and concentric resistance training protocols. J Strength Cond Res January 2010;24. [3] Colliander EB, Tesch PA. Effects of eccentric and concentric muscle actions in resistance training. Acta Physiol Scand 1990;140:31–9. [4] Farthing JP, Chilibeck PD. The effects of eccentric and concentric training at different velocities on muscle hypertrophy. Eur J Appl Physiol 2003;89:578–86. [5] Hather BM, Tesch PA, Buchanan P, Dudley GA. Influence of eccentric actions on skeletal muscle adaptations to resistance training. Acta Physiol Scand 1991;143:177–85. [6] Hollander DB, Kraemer RR, Kilpatrick MW, Ramadan ZG, Reeves GV, Francois M, Hebert EP, Tryniecki JL. Maximal eccentric and concentric strength discrepancies between young men and women for dynamic resistance exercise. J Strength Cond Res 2007;21:34–40. [7] Hortobagyi T, Barrier J, Beard D, Braspennincx J, Koens P, Devita P, Dempsey L, Lambert J. Greater initial adaptations to submaximal muscle lengthening than maximal shortening. J Appl Physiol (1985) 1996;81:1677–82. [8] Kyrolainen H, Komi PV. Differences in mechanical efficiency between power- and endurance-trained athletes while jumping. Eur J Appl Physiol Occup Physiol 1995;70:36–44. [9] Kyrolainen H, Komi PV. The function of neuromuscular system in maximal stretch-shortening cycle exercises: comparison between powerand endurance-trained athletes. J Electromyogr Kinesiol 1995;5:15–25. [10] Roig M, O’Brien K, Kirk G, Murray R, McKinnon P, Shadgan B, Reid WD. The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis. Br J Sports Med 2009;43:556–68. [11] Schoenfeld BJ. Does exercise-induced muscle damage play a role in skeletal muscle hypertrophy? J Strength Cond Res 2012;26:1441–53. [12] Seger JY, Thorstensson A. Effects of eccentric versus concentric training on thigh muscle strength and EMG. Int J Sports Med 2005;26:45–52. [13] Seyfarth A, Blickhan R, Van Leeuwen JL. Optimum take-off techniques and muscle design for long jump. J Exp Biol 2000;203:741–50. [14] Vos EJ, Harlaar J, van Ingen Schenau GJ. Electromechanical delay during knee extensor contractions. Med Sci Sports Exerc 1991;23:1187–93.

5.  MINERALS AND SUPPLEMENTS IN MUSCLE BUILDING