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Changes in stature during exercise and sports training
AppfiedErgonomics 1991, 22.5,308-311
Ergonomics and sport
Changes in stature during exercise and sports training T. Reilly*, M.G. Boocock*, G. Garbutt*, J.D.G. Troup t and K. Linget *Centre for Sport and ExerciseSciences,Liverpool Polytechnic,Byrom Street, Liverpool L3 3AF, UK t Department of Orthopaedicand Accident Surgery, Royal Liverpool Hospital, PrescottStreet, Liverpool, UK Shrinkage in stature is used in ergonomics and sports contexts as an index of load on the spine. Measurement is now computer-aided to facilitate data collection. Applications of the technique to sport and exercise have included evaluations of weight-training, running and jumping drills. The technique has also been employed in assessing procedures for spinal unloading such as gravity inversion. Future applications include investigations of procedures used to prevent back injury as well as studies of sports that impose high transient loads on the spine.
Keywords: Jumping, running, spinal shrinkage, weight-training
Introduction Stature is a fundamental variable in anthropometry and ergonomics. For conventional descriptive purposes, measurement to the nearest centirnetre has been considered satisfactory. Much more precise measurement is possible in assessment of transient intra-individual changes if the subject's posture is finely controlled whilst observations are being made. Compressive loading of the spine causes a reduction in the length of the spinal column which is reflected in changes in stature and is referred to as shrinkage.
The amount of shrinkage is related to the magnitude of the compressive load on the spine: consequently, shrinkage has been used as an index of spinal loading (Corlett et al, 1987). Changes in total body length have been employed to examine the effects of physical regimens that load the spine. Additionally, the technique has been used to evaluate manoeuvres for unloading the spine such as traction, gravity inversion and the so-called Fowler position - supine posture, feet supported on a chair, hip at about 45 ° flexion (Boocock et al, 1988).
Applied Ergonomics
October 1991
Computer-aided stadiometry Special apparatus which allows intra-individual variation in spinal configuration to be accommodated and intraindividual postures to be reproduced accurately under relaxed conditions has been developed (Corlett et al, 1987). Relaxation is achieved by inclining the subject backwards by up to 15 °. Design features control the position and contour of the spinal curves, position of head and limbs, head angle in the sagittal plane, and weight distribution between heels and forefoot. The phase of the respiratory cycle is also controlled, after subjects have been given a brief training session to accustom them to the apparatus.
The spinal column represents approximately 40% of the total body length, and about one-third of its overall length is occupied by intervertebral discs. As the spine is subjected to compressive forces, the discs lose height due to elimination of fluid from their nucleus pulposus. This occurs once the applied load exceeds the sum of the imbibition pressure of the nucleus pulposus complex and the osmotic gradient across the disc membranes. In addition to fluid exchange, extension and contraction of the fibres of the disc's annulus fibrosus are also implicated in disc height losses. Changes within the spinal column are largely responsible for the shrinkage in stature, alteration in other anatomical structures being thought negligible.
308
The present purpose is to summarise some of the applications of fine measurement of stature to date. The focus is mainly on studies of exercise regimens with reference to recovery periods where appropriate. The measurement device is explained first, before findings of experimental work are presented. Some additional applications in future work are suggested.
The apparatus used at Nottingham, Link6ping, Helsinki and Liverpool differs in minor respects, but measurement error reported in each laboratory is small (Corlett et al, 1987). The standard practice is to commence experimental work only when subjects can produce 10 consecutive measurements of alteration in stature with a standard deviation of less than 0.5 mm. Earlier versions of the stadiometer were described by Tyrrell et al (1985) and Boocock et al (1986). The system currently used at Liverpool employs a microcomputer for calibration purposes, for controlling the measurement protocol, and finally for recording observations (Fig. 1).
0003-6870/91/05 0308-04 $03.00 © 1991 Butterworth-Heinemann Ltd
Ergonomim and sport up to 50 mm of travel. The rod activates upon a Mercer dial gauge having a precision of 0-01 mm. Two strain gauges on opposite faces of a spring travelling on the upper surface of the disc are fed with current from an electronic amplifier and transfer vertical displacement into an electrical signal. The change in voltage passing through the strain gauge is linearly related to vertical displacement of the head disc. The voltage signal is passed to a BBC microcomputer for A - D conversion. The computer displays, processes and stores the data on floppy disc. Quality control of data collection is incorporated into the computer program during subjects' first introduction to the procedure in which it is established that repeatable measurement is obtainable (SD of less than 0.5 mm). Later, it is achieved by means of the procedure already explained.
Weight-training Static shoulder loads using rucksack and barbells have been examined by Tyrrell et al (1985). Observations were made at 2-min intervals during 20 min of experimental loading, measurement taking about 2 min. Shrinkage of 5.45 mm was incurred with the 10 kg rucksack and 5.14 mm with the barbell. Shrinkage increased with increased barbell loading to 7.11 mm (20 kg), 9-42 mm (30 kg), and 11-2 mm (40 kg). Dynamic loading, induced by lifting a barbell (from floor using weight-lifter's crouch position to knuckle height standing) 12 times per minute for 20 rnin, produced a greater shrinkage than static loading. This difference was 3.3 mm for a 40 kg load.
Fig. 1
Subject is in position on the stadiometer. Successive observations are displayed on the monitor
The central pillar, supported by an aluminium framework, possesses adjustable rods and plates activating on microswitches. These are used to contact and record prominent points including buttocks, lumbar and cervical curves, midscapulae and head. An electronic weighing scale is set into the base to monitor equal weight distribution through both feet. Head alignment is standardised by use of an infra-red emitter on spectacles worn by the subject and an infra-red receiver set into an adjustable panel in front of the subject's face. The panel also has five light-emitting diodes (LEDs) activated by the microswitches. The LEDs give feedback of the required posture to the subject and measurement auto. matically proceeds when all seven (including one for weight and one linked to the head aligning device) are illuminated. A plastic disc, 150 mm diameter, resting carefully on top of the subject's head, is connected to a vertical rod. This can be located at various positions on the main frame to accommodate persons of various height, each time allowing
Circuit weight-training, as employed for stressing the oxygen transport system rather than muscle conditioning, has also been examined. Nine males rotating around nine exercise stations for 25 min were found to lose on average 5 49 mm in stature (Leatt et al, 1986). The weights varied from 14 to 32 kg for the different exercises. A comparison of results with those of Tyrrell et al (1985), who found shrinkage of 7-11 mm with 20 kg dynamic loading over 20 min, would suggest that the strain on the spine may have been eased by some of the exercises in the circuit. However, the data may not be directly comparable due to the manual control of the procedures and the more primitive apparatus used in the pioneering work of Tyrrell et al.
Ten female subjects repeating a sequence of eight weighttraining exercises for 20 min were examined by Wilby et al (1987). The regimen was performed immediately after rising from sleep and in the evening at 22.00 hours. A greater loss of height was observed in the morning than in the evening, mean values being 5.4 and 4.33 mm, respectively. This difference was attributed to the diurnal variation in stature. The rate of change in stature varies throughout the day, being greatest in the morning, whereas disc imbibition and recovery is rapid in the early hours of sleep. A peak-to-trough variation in stature of 15-4 mm and 19.3 mm has been shown for females (Wilby et al, 1987) and males (Reilly et al, 1984), respectively. Regaining height during recovery in a relaxed standing posture after weight-training has been found, in general, to
Applied Ergonomics
October 1991
309
Ergonomics and sport be proportional to loading. Between 74-79% of the losses incurred in static loading were regained within 10 min in the study of Tyrrell et al (1985). The height regained in Fowler's position in a similar period in fact exceeded the height lost during loading.
Running Running, particularly on road surfaces, induces repetitive loading of the spine. Shrinkage in experienced and novice runners exercising on a treadmill at 12-2 km/h for 30 min was examined by Leatt e t al (1986). Loss of stature amounted to 2.35 mm for the experienced group and was 3.26 mm for the other, the difference being nonsignificant. The experienced runners did a further 19 km at 14.6 km/h and lost another 7.79mm. It appeared that the duration of the run was an important factor. Effects of running continously at 10 km/h for 40 rain have been compared with those due to alternating a fast and slow pace regularly over the same time and covering the same overall distance. The pace fluctuated between jogging at 7 km/h and 21 km/h sprints. No significant difference was found between the intermittent and the continuous running in terms of spinal shrinkage, once the distance and duration of exercise were matched (Reilly et al, 1988). The influence of running intensity on shrinkage was examined by Garbutt et al (1989). Five male runners did three 30-min runs at 70%, 85% and 100% of their competitive marathon pace. In the first 15 min, mean losses of stature were 4.25, 3.37 and 3-97 mm for the increasing intensities of running, these differences being nonsignificant. In the final 15 min, further stature losses of 0"91,1-06 and 2.63 mm were noted, the greater shrinkage at the fastest speed being significant. It is possible that greater rates of shrinkage are incurred at higher intensities corresponding to half-marathon and 10 km race pace. The influence of the quality of the running shoe on shrinkage may be important but this has yet to be investigated. In a subsequent study, Garbutt et al (1990) examined the effect of three running speeds on two groups of runners, one with chronic low.back pain. The two groups of seven male marathon runners ran at 70%, 85% and 100% of their marathon race pace for 30 min on separate occasions. Before and after e.xercise the subjects were seated for 20 min with the lumbar spine supported. Stature was measured before pre-exercise sitting, before running, after 15 min of running, after 30 min of running and after post-exercise sitting. There were no significant differences in the responses to the three running regimens between the groups. Shrinkage was greater in the first 15 min, being 3.26 (-+ 2-78) mm compared with 2"12 (-+ 1"61) mm for the second half of the run (.t7 < 0-05). The faster the running speed, the greater was the resultant shrinkage. The 70%, 85% and 100% conditions caused 3.37 (-+ 2.38), 5.10 (+ 1 "90) and 7"69 (-+ 3.69) mm of shrinkage, respectively (p < 0-005). These observations suggest that in this group of runners who were able to maintain their training despite continuing back pain, tower.back pain was independent of the shrinkage induced by running. Further research was recommended to determine the effects of longer duration runs oil spinal shrinkage.
310
AppliedErgonomics
October 1991
Jumping exercises Jumping and bounding exercises have been increasingly implemented in training regimens to develop leg power. Landing from such exercises induces high impact forces which the human body must seek to absorb. The intervertebral disc is the principal shock absorber of the spine responsible for dissipating these high forces. Shrinkage measurements have been implemented to study the spinal loading resulting from such jumping and bounding exercises. A regimen of ten sets of five standing broad jumps with 15-s recovery between each set, lasting on average 6.7 min, was found to cause a mean loss in stature of 1.7 mm (Boocock et al, 1988). To assess the potential benefits of unloading the spine pre-exercise, thereby increasing the discs' functional ability to absorb compressive loading, a 10-min period of gravity inversion (Fig. 2) was undertaken prior to the same exercise period. (Inverting the subject at 50 ° has been found to increase stature more than a 90 ° inclination, which in turn was superior to the Fowler position (Leatt et al, 1985).) The unloading period caused a mean increase in stature of 2.7 mm and the resulting exercise period when performed immediately after inversion induced twice the magnitude of shrinkage, 3-5 mm. It was concluded that the benefits gained by spinal unloading pre-exercise are short-lasting. Similarly, drop-jumping exercises, which involve athletes dropping from a predetermined height and performing a rebound jump immediately on landing, have been noted to induce shrinkage. Five sets of five drop-jumps from a height of 1 m, rebounding over a hurdle 0"5 m high, caused a mean loss in stature of 1.74 mm (Boocock e t al, 1989). On this occasion, post-exercise unloading was investigated with a 20-rain gravity inversion period directly following the
Fig. 2
Gravity inversion of subject at 50 ° angle
Ergonomics and sport exercise session. This inversion period caused an increase in stature of 5-18 mm compared with 0.76 mm from a standing period of similar duration. Stature was maintained for a further 40 min in which subjects stood. During the 40 min following inversion there was a rapid loss in stature of 4<)7 mm. For the session involving standing postexercise this same period caused little alteration in stature, 0.04 mm. It was noted that 30 rain into this 40-rain recovery period there was no significant difference for stature alterations between the two experimental conditions. It was again concluded that the effects of unloading are only short-lived. Further, it should be recognised that in some people a rapid regain in stature on unloading may adversely affect the dynamic response characteristics of the spine. If major exertion is undertaken immediately the rest-period is ended, a brief warm-up may be advisable.
References Boocock, M., Reilly, T., Linge, K., and Troup, J.D.G. 1986, 'Fine measurement of stature for studying spinal loading'. In: T. Reilly, J. Watkins and J. Borms (Eds). Kinanthropometry III. E. and F.N. Spon, London, 9 8 103.
Boocock, M.G., Garbutt, G., Reilly, T., Linge, K., and Troup, J.D.G. 1988,Ergonomics, 31, 1631-1637. The effects of gravity inversion on exercise-induced spinal loading.
Boocock, M.G., Garbutt, G., Linge, K., Reilly, T., and Troup, J.D.G. 1989, Med SciSports Exerc, 22,385-390. Changes in stature following drop-jumping and postexercise gravity inversion.
Corlett, E.N., Eklund, J.A.E., Reilly, T., and Troup, J.D.G. 1987, Appl Ergonomics, 18, 6 5 - 7 1 . Assessment of workload from measurements of stature.
Future applications The series of studies reviewed here has shown that spinal shrinkage can be used as an index of the biomechanical loads on the spine in various sporting contexts. Results have shown also that changes in stature may be related to psychophysical ratings ( T r o u p e t al, 1985). Use of the technique may be extended to other activities that impose transient loads on the spine. These include bowling in cricket, driving in golf, landing in gymnastics, and many others. The effectiveness of different designs of sporting equipment in reducing the forces imposed on the spine may also be evaluated using shrinkage as a criterion. This might include, for instance, rucksacks for mountaineers, golf clubs, and so on. The technique will also be helpful in evaluating regimens used in protecting against back injury. These include unloading manoeuvres such as gravity inversion and the Fowler posture. They also include warm-up and warm. down procedures. The protective role of the back muscles can also be investigated, as back strength was found in one study to be inversely related to the amount of shrinkage 0Vilby et al, 1987). The extent to which shrinkage can be used in screening for potential back pain sufferers remains to be established.
Acknowledgement The support of the Health Promotion Research Trust in funding this work is gratefully acknowledged.
Garbutt, G., Boocock, M.G., Reilly, T., and Troup, J.D.G. 1989,J Sports Sci, 7, 77. The effect of running speed on spinal shrinkage.
Garbutt, G., Boocoek, M.G., Reilly, T., and Troup, J.D.G. 1990, Med Sci Sports Exerc, 2 2 , 7 6 9 - 7 7 2 . Running speed and spinal shrinkage in runners with and without low-back pain. Leatt, P., Reilly, T., and Troup, J.D.G. 1985, 'Unloading the spine'. In: D. Oborne (Ed). Contemporary Ergonomics 1985, Taylor & Francis, London, pp 227-232. Leatt, P., Reilly, T., and Troup, J.D.G. 1986,BritJ Sports Med, 20, 119-124. Spinal loading during circuit weighttraining and running. Reilly, T., Tyrrell, A., and Troup, J.D.G. 1984, Chronobiol Int, 1 , 1 2 1 - 1 2 6 . Circadian variation in human stature. Reilly, T., Grant, R., Linge, K., and Troup, J.D.G. 1988, 'Spinal shrinkage during treadmill running'. Abstracts: New Horizons in Human Movement Vol. III, p 412, Cheonan: SOSCOC.
Troup, J.D.G., Reilly, T., Eklund, J.A.E., and Leatt, P. 1985, Stress Med, 1 , 3 0 3 - 3 0 7 . Changes in stature with spinal loading and their relation to the perception of exertion or discomfort. Tyrrell, A.R., Reilly, T., and Troup, J.D.G. 1985, Spine, 10, 161-164. Circadian variation in stature and the effects of spinal loading. Wilby, J., Linge, K., Reilly, T., and Troup, J.D.G. 1987j Ergonomics, 30, 4 7 - 5 4 . Spinal shrinkage in females: circadian variation and the effects of circuit weight-training.
Applied Ergonomics October 1991
311
Ergonomics and sport
Changes in stature during exercise and sports training T. Reilly*, M.G. Boocock*, G. Garbutt*, J.D.G. Troup t and K. Linget *Centre for Sport and ExerciseSciences,Liverpool Polytechnic,Byrom Street, Liverpool L3 3AF, UK t Department of Orthopaedicand Accident Surgery, Royal Liverpool Hospital, PrescottStreet, Liverpool, UK Shrinkage in stature is used in ergonomics and sports contexts as an index of load on the spine. Measurement is now computer-aided to facilitate data collection. Applications of the technique to sport and exercise have included evaluations of weight-training, running and jumping drills. The technique has also been employed in assessing procedures for spinal unloading such as gravity inversion. Future applications include investigations of procedures used to prevent back injury as well as studies of sports that impose high transient loads on the spine.
Keywords: Jumping, running, spinal shrinkage, weight-training
Introduction Stature is a fundamental variable in anthropometry and ergonomics. For conventional descriptive purposes, measurement to the nearest centirnetre has been considered satisfactory. Much more precise measurement is possible in assessment of transient intra-individual changes if the subject's posture is finely controlled whilst observations are being made. Compressive loading of the spine causes a reduction in the length of the spinal column which is reflected in changes in stature and is referred to as shrinkage.
The amount of shrinkage is related to the magnitude of the compressive load on the spine: consequently, shrinkage has been used as an index of spinal loading (Corlett et al, 1987). Changes in total body length have been employed to examine the effects of physical regimens that load the spine. Additionally, the technique has been used to evaluate manoeuvres for unloading the spine such as traction, gravity inversion and the so-called Fowler position - supine posture, feet supported on a chair, hip at about 45 ° flexion (Boocock et al, 1988).
Applied Ergonomics
October 1991
Computer-aided stadiometry Special apparatus which allows intra-individual variation in spinal configuration to be accommodated and intraindividual postures to be reproduced accurately under relaxed conditions has been developed (Corlett et al, 1987). Relaxation is achieved by inclining the subject backwards by up to 15 °. Design features control the position and contour of the spinal curves, position of head and limbs, head angle in the sagittal plane, and weight distribution between heels and forefoot. The phase of the respiratory cycle is also controlled, after subjects have been given a brief training session to accustom them to the apparatus.
The spinal column represents approximately 40% of the total body length, and about one-third of its overall length is occupied by intervertebral discs. As the spine is subjected to compressive forces, the discs lose height due to elimination of fluid from their nucleus pulposus. This occurs once the applied load exceeds the sum of the imbibition pressure of the nucleus pulposus complex and the osmotic gradient across the disc membranes. In addition to fluid exchange, extension and contraction of the fibres of the disc's annulus fibrosus are also implicated in disc height losses. Changes within the spinal column are largely responsible for the shrinkage in stature, alteration in other anatomical structures being thought negligible.
308
The present purpose is to summarise some of the applications of fine measurement of stature to date. The focus is mainly on studies of exercise regimens with reference to recovery periods where appropriate. The measurement device is explained first, before findings of experimental work are presented. Some additional applications in future work are suggested.
The apparatus used at Nottingham, Link6ping, Helsinki and Liverpool differs in minor respects, but measurement error reported in each laboratory is small (Corlett et al, 1987). The standard practice is to commence experimental work only when subjects can produce 10 consecutive measurements of alteration in stature with a standard deviation of less than 0.5 mm. Earlier versions of the stadiometer were described by Tyrrell et al (1985) and Boocock et al (1986). The system currently used at Liverpool employs a microcomputer for calibration purposes, for controlling the measurement protocol, and finally for recording observations (Fig. 1).
0003-6870/91/05 0308-04 $03.00 © 1991 Butterworth-Heinemann Ltd
Ergonomim and sport up to 50 mm of travel. The rod activates upon a Mercer dial gauge having a precision of 0-01 mm. Two strain gauges on opposite faces of a spring travelling on the upper surface of the disc are fed with current from an electronic amplifier and transfer vertical displacement into an electrical signal. The change in voltage passing through the strain gauge is linearly related to vertical displacement of the head disc. The voltage signal is passed to a BBC microcomputer for A - D conversion. The computer displays, processes and stores the data on floppy disc. Quality control of data collection is incorporated into the computer program during subjects' first introduction to the procedure in which it is established that repeatable measurement is obtainable (SD of less than 0.5 mm). Later, it is achieved by means of the procedure already explained.
Weight-training Static shoulder loads using rucksack and barbells have been examined by Tyrrell et al (1985). Observations were made at 2-min intervals during 20 min of experimental loading, measurement taking about 2 min. Shrinkage of 5.45 mm was incurred with the 10 kg rucksack and 5.14 mm with the barbell. Shrinkage increased with increased barbell loading to 7.11 mm (20 kg), 9-42 mm (30 kg), and 11-2 mm (40 kg). Dynamic loading, induced by lifting a barbell (from floor using weight-lifter's crouch position to knuckle height standing) 12 times per minute for 20 rnin, produced a greater shrinkage than static loading. This difference was 3.3 mm for a 40 kg load.
Fig. 1
Subject is in position on the stadiometer. Successive observations are displayed on the monitor
The central pillar, supported by an aluminium framework, possesses adjustable rods and plates activating on microswitches. These are used to contact and record prominent points including buttocks, lumbar and cervical curves, midscapulae and head. An electronic weighing scale is set into the base to monitor equal weight distribution through both feet. Head alignment is standardised by use of an infra-red emitter on spectacles worn by the subject and an infra-red receiver set into an adjustable panel in front of the subject's face. The panel also has five light-emitting diodes (LEDs) activated by the microswitches. The LEDs give feedback of the required posture to the subject and measurement auto. matically proceeds when all seven (including one for weight and one linked to the head aligning device) are illuminated. A plastic disc, 150 mm diameter, resting carefully on top of the subject's head, is connected to a vertical rod. This can be located at various positions on the main frame to accommodate persons of various height, each time allowing
Circuit weight-training, as employed for stressing the oxygen transport system rather than muscle conditioning, has also been examined. Nine males rotating around nine exercise stations for 25 min were found to lose on average 5 49 mm in stature (Leatt et al, 1986). The weights varied from 14 to 32 kg for the different exercises. A comparison of results with those of Tyrrell et al (1985), who found shrinkage of 7-11 mm with 20 kg dynamic loading over 20 min, would suggest that the strain on the spine may have been eased by some of the exercises in the circuit. However, the data may not be directly comparable due to the manual control of the procedures and the more primitive apparatus used in the pioneering work of Tyrrell et al.
Ten female subjects repeating a sequence of eight weighttraining exercises for 20 min were examined by Wilby et al (1987). The regimen was performed immediately after rising from sleep and in the evening at 22.00 hours. A greater loss of height was observed in the morning than in the evening, mean values being 5.4 and 4.33 mm, respectively. This difference was attributed to the diurnal variation in stature. The rate of change in stature varies throughout the day, being greatest in the morning, whereas disc imbibition and recovery is rapid in the early hours of sleep. A peak-to-trough variation in stature of 15-4 mm and 19.3 mm has been shown for females (Wilby et al, 1987) and males (Reilly et al, 1984), respectively. Regaining height during recovery in a relaxed standing posture after weight-training has been found, in general, to
Applied Ergonomics
October 1991
309
Ergonomics and sport be proportional to loading. Between 74-79% of the losses incurred in static loading were regained within 10 min in the study of Tyrrell et al (1985). The height regained in Fowler's position in a similar period in fact exceeded the height lost during loading.
Running Running, particularly on road surfaces, induces repetitive loading of the spine. Shrinkage in experienced and novice runners exercising on a treadmill at 12-2 km/h for 30 min was examined by Leatt e t al (1986). Loss of stature amounted to 2.35 mm for the experienced group and was 3.26 mm for the other, the difference being nonsignificant. The experienced runners did a further 19 km at 14.6 km/h and lost another 7.79mm. It appeared that the duration of the run was an important factor. Effects of running continously at 10 km/h for 40 rain have been compared with those due to alternating a fast and slow pace regularly over the same time and covering the same overall distance. The pace fluctuated between jogging at 7 km/h and 21 km/h sprints. No significant difference was found between the intermittent and the continuous running in terms of spinal shrinkage, once the distance and duration of exercise were matched (Reilly et al, 1988). The influence of running intensity on shrinkage was examined by Garbutt et al (1989). Five male runners did three 30-min runs at 70%, 85% and 100% of their competitive marathon pace. In the first 15 min, mean losses of stature were 4.25, 3.37 and 3-97 mm for the increasing intensities of running, these differences being nonsignificant. In the final 15 min, further stature losses of 0"91,1-06 and 2.63 mm were noted, the greater shrinkage at the fastest speed being significant. It is possible that greater rates of shrinkage are incurred at higher intensities corresponding to half-marathon and 10 km race pace. The influence of the quality of the running shoe on shrinkage may be important but this has yet to be investigated. In a subsequent study, Garbutt et al (1990) examined the effect of three running speeds on two groups of runners, one with chronic low.back pain. The two groups of seven male marathon runners ran at 70%, 85% and 100% of their marathon race pace for 30 min on separate occasions. Before and after e.xercise the subjects were seated for 20 min with the lumbar spine supported. Stature was measured before pre-exercise sitting, before running, after 15 min of running, after 30 min of running and after post-exercise sitting. There were no significant differences in the responses to the three running regimens between the groups. Shrinkage was greater in the first 15 min, being 3.26 (-+ 2-78) mm compared with 2"12 (-+ 1"61) mm for the second half of the run (.t7 < 0-05). The faster the running speed, the greater was the resultant shrinkage. The 70%, 85% and 100% conditions caused 3.37 (-+ 2.38), 5.10 (+ 1 "90) and 7"69 (-+ 3.69) mm of shrinkage, respectively (p < 0-005). These observations suggest that in this group of runners who were able to maintain their training despite continuing back pain, tower.back pain was independent of the shrinkage induced by running. Further research was recommended to determine the effects of longer duration runs oil spinal shrinkage.
310
AppliedErgonomics
October 1991
Jumping exercises Jumping and bounding exercises have been increasingly implemented in training regimens to develop leg power. Landing from such exercises induces high impact forces which the human body must seek to absorb. The intervertebral disc is the principal shock absorber of the spine responsible for dissipating these high forces. Shrinkage measurements have been implemented to study the spinal loading resulting from such jumping and bounding exercises. A regimen of ten sets of five standing broad jumps with 15-s recovery between each set, lasting on average 6.7 min, was found to cause a mean loss in stature of 1.7 mm (Boocock et al, 1988). To assess the potential benefits of unloading the spine pre-exercise, thereby increasing the discs' functional ability to absorb compressive loading, a 10-min period of gravity inversion (Fig. 2) was undertaken prior to the same exercise period. (Inverting the subject at 50 ° has been found to increase stature more than a 90 ° inclination, which in turn was superior to the Fowler position (Leatt et al, 1985).) The unloading period caused a mean increase in stature of 2.7 mm and the resulting exercise period when performed immediately after inversion induced twice the magnitude of shrinkage, 3-5 mm. It was concluded that the benefits gained by spinal unloading pre-exercise are short-lasting. Similarly, drop-jumping exercises, which involve athletes dropping from a predetermined height and performing a rebound jump immediately on landing, have been noted to induce shrinkage. Five sets of five drop-jumps from a height of 1 m, rebounding over a hurdle 0"5 m high, caused a mean loss in stature of 1.74 mm (Boocock e t al, 1989). On this occasion, post-exercise unloading was investigated with a 20-rain gravity inversion period directly following the
Fig. 2
Gravity inversion of subject at 50 ° angle
Ergonomics and sport exercise session. This inversion period caused an increase in stature of 5-18 mm compared with 0.76 mm from a standing period of similar duration. Stature was maintained for a further 40 min in which subjects stood. During the 40 min following inversion there was a rapid loss in stature of 4<)7 mm. For the session involving standing postexercise this same period caused little alteration in stature, 0.04 mm. It was noted that 30 rain into this 40-rain recovery period there was no significant difference for stature alterations between the two experimental conditions. It was again concluded that the effects of unloading are only short-lived. Further, it should be recognised that in some people a rapid regain in stature on unloading may adversely affect the dynamic response characteristics of the spine. If major exertion is undertaken immediately the rest-period is ended, a brief warm-up may be advisable.
References Boocock, M., Reilly, T., Linge, K., and Troup, J.D.G. 1986, 'Fine measurement of stature for studying spinal loading'. In: T. Reilly, J. Watkins and J. Borms (Eds). Kinanthropometry III. E. and F.N. Spon, London, 9 8 103.
Boocock, M.G., Garbutt, G., Reilly, T., Linge, K., and Troup, J.D.G. 1988,Ergonomics, 31, 1631-1637. The effects of gravity inversion on exercise-induced spinal loading.
Boocock, M.G., Garbutt, G., Linge, K., Reilly, T., and Troup, J.D.G. 1989, Med SciSports Exerc, 22,385-390. Changes in stature following drop-jumping and postexercise gravity inversion.
Corlett, E.N., Eklund, J.A.E., Reilly, T., and Troup, J.D.G. 1987, Appl Ergonomics, 18, 6 5 - 7 1 . Assessment of workload from measurements of stature.
Future applications The series of studies reviewed here has shown that spinal shrinkage can be used as an index of the biomechanical loads on the spine in various sporting contexts. Results have shown also that changes in stature may be related to psychophysical ratings ( T r o u p e t al, 1985). Use of the technique may be extended to other activities that impose transient loads on the spine. These include bowling in cricket, driving in golf, landing in gymnastics, and many others. The effectiveness of different designs of sporting equipment in reducing the forces imposed on the spine may also be evaluated using shrinkage as a criterion. This might include, for instance, rucksacks for mountaineers, golf clubs, and so on. The technique will also be helpful in evaluating regimens used in protecting against back injury. These include unloading manoeuvres such as gravity inversion and the Fowler posture. They also include warm-up and warm. down procedures. The protective role of the back muscles can also be investigated, as back strength was found in one study to be inversely related to the amount of shrinkage 0Vilby et al, 1987). The extent to which shrinkage can be used in screening for potential back pain sufferers remains to be established.
Acknowledgement The support of the Health Promotion Research Trust in funding this work is gratefully acknowledged.
Garbutt, G., Boocock, M.G., Reilly, T., and Troup, J.D.G. 1989,J Sports Sci, 7, 77. The effect of running speed on spinal shrinkage.
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