Eur J Appl Physiol (1992) 65:370-375

Applied Physiology Journal o f

and Occupattonal Physiology © Spnnger~Verlag1992

Effects of isokinetic training of the knee extensors on isometric strength and peak power output during cycling A. F. Mannion 1, P. M. Jakeman 1, and P. L. T. Willan 2

1 School of Sport and Exercise Sciences, Universityof Birmingham,BirminghamB15 2TT, England 2 Department of Ceil and Structural Biology,Universityof Manchester, Manchester M13 9PT, England Accepted April 22, 1992

Summary. Isokinetic training of right and left quadriceps femoris was undertaken three times per week for 16 weeks. One group of subjects (n -- 13) trained at an angular velocity of 4.19rad's -1 and a second group (n = 10) at 1.05 rad.s-1. A control group (n = 10) performed no training. Maximal voluntary contraction (MVC) of the quadriceps, and peak pedal velocity (Vp,peak) and peak power output (Wpeak) during all-out cycling (against loads equivalent to 9, 10, 11, 12, 13 and 14% MVC) were assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of the performance variables (P>0.05). No significant difference in MVC was observed for any group after the 16-week period (P=0.167). The post-training increases in average Wp~k (70/0) and Vp,peak (6%) during the cycle tests were each significantly different from the control group response (P=0.018 and P=0.008, respectively). It is concluded that 16 weeks of isokinetic strength training of the knee extensors is able to significantly improve Pp,peak and Wpeak during sprint cycling, an activity which demands considerable involvement of the trained muscle group but with its own distinct pattern of coordination. Key words: Isokinetic training - Strength - Maximum voluntary contraction - Knee extensors - Sprint cycle power output

Introduction

Isokinetic strength training is becoming increasingly popular as a method by which to improve the strength and/or power output of major muscle groups. A number of features of this mode of training - including safety, self-regulation (with respect to overload), simplicity Correspondence to: A. F. Mannion, Comparative Orthopaedic Research Unit, Departments of Anatomy and Orthopaedic Surgery, University of Bristol, Park Row, Bristol BS1 5LS, England

of technique and the generation of maximum tension throughout the full range of motion (see Osternig 1986) - combine to render it a preferable alternative to freeweight lifting or the use of conventional isotonic resistance machines. Many studies have sought to evaluate the extent, and transferability, of improvements in strength or power elicited by training isokinetically at differing angular velocities (Caiozzo et al. 1981; Coyle et al. 1981; Ewing et al. 1990; Kanehisa and Myashita 1983; Narici et al. 1989; Petersen et al. 1990). From these studies, it has become apparent that training-induced improvements are frequently confined to the performance of tasks which closely simulate the training manoeuvre in their mode of action and velocity. This specificity of training is particularly noticeable when training is conducted for a relatively short period of time; in view of the known neural adaptations to training - which account almost exclusively for the gains in strength/power observed during the first 6-8 weeks of training (Jones et al. 1989; Komi 1986) - it is not surprising that the improvements displayed during performance of the training task are not transferable to other activities. Beyond 8 weeks of training, peripheral adaptations in the muscle - such as an increase in the myofibrillar material or alterations in metabolic and/or contractile characteristics - can be expected to contribute to the increasing gains in muscle strength/power (Hainaut and Duchateau 1989; Komi 1986; MacDougall et al. 1977). Such quantitative and qualitative changes in the muscle ought then to allow for an improved performance in any task (of a similar exercise intensity) which involves substantial usage of the trained muscle group. Unfortunately, the literature is largely unable to support this hypothesis; few training studies are conducted beyond the "learning phase", and those that are seldom examine the transferability, to other tasks, of the newly acquired strength/power. This is somewhat surprising, since the majority of individuals who undertake strength training programmes do so in the belief that their improved strength will enhance performance in their own particular sporting activity. In one study, it was shown that 12

371 weeks o f isotonic strength t r a i n i n g of the quadriceps elicited a 160-200% increase in the weights lifted in training, a n d a 3 - 2 0 % increase in quadriceps m a x i m a l v o l u n tary c o n t r a c t i o n (MVC), b u t h a d n o significant effect o n the peak power o u t p u t (Wpeak) generated d u r i n g isokinetic cycling ( R u t h e r f o r d et al. 1986). T h e r e a s o n for the lack o f a t r a n s f e r e n c e effect was u n c e r t a i n , a l t h o u g h it was suggested that even 12 weeks o f t r a i n i n g m a y have b e e n i n s u f f i c i e n t to extend the subjects b e y o n d the " l e a r n i n g phase" d u r i n g this type of t r a i n i n g (Rutherford et al. 1986). N o c o m p a r a b l e studies i n v o l v i n g isokinetic t r a i n i n g o f a long d u r a t i o n are r e p o r t e d in the literature. The present study was therefore designed to e x a m i n e the effects o f isokinetic t r a i n i n g o f the knee extensors o n the isometric strength o f the muscle, a n d o n the peak pedal velocity (Vp,peak) a n d Wpeak d u r i n g sprint cycling. C o n s t a n t load cycling with accelerating/decelerating m o v e m e n t s was chosen because it is a f u n c t i o n a l activity which d e m a n d s s u b s t a n t i a l usage o f the q u a d r i ceps, yet in a different p a t t e r n of c o o r d i n a t i o n f r o m the training manoeuvre.

Table 1. Mean (SD) of physical characteristics of the subjects

Training group

Sub- Age jects a (years)

Height (cm)

Mass (kg)

(C) Control

4M 6F 7M 6F 8M 2F b

1.80 (0.11) 1.67 (0.07) 1.81 (0.06) 1.66(0.07) 1.78 (0.06) 1.69 (0.06)

83.7 (17.8) 64.2 (8.2) 82.7 (9.1) 59.4 (4.8) 72.9 (9.4) 70.4 (12.7)

(TF) Training at 4.19rad.s -~ (TS) Training at 1.05 rad.s -~

a M, Men; F, Women b Three women, originally in group TS, withdrew from the study during the 1st month Table 2. Training schedules

Group

Training schedule

Control (n = 10) Training: leg extensions at 4.19 rad's -1 (n = 13)

(C) (TF)

Training leg extensions at 1.05 rad. s - 1 (n = 1O)

(TS)

Methods

Subjects Thirty-six healthy human volunteers (19 men, 17 women) agreed to participate in the study, which was approved by the local ethical committee. The subjects were physically active members of a college sports science/physical education department. Each was informed of the purpose and potential risks of the study before his/ her written voluntary consent was obtained. The subjects were randomly assigned to one of three groups: C (control), TF (training at 4.19rad.s -1) or TS (training at 1.05 rad.s-1). Three women from group TS ceased training after 2 weeks such that in total 33 subjects completed the study. The physical characteristics of the subjects are shown in Table 1.

Training Subjects trained for a total of 16 weeks using an isokinetic leg extension machine (Orthotron KT2, Cybex). The training programmes (Table 2) were designed such that the two groups were matched in terms of the total work done during a single training session, following the guidelines of Rosier et al. (1986). Training sessions were carried out in pairs, under supervision, and individuals were instructed to make a maximal effort throughout the full range of motion during each repetition. The peak torque generated during knee extension was displayed on an analogue dial (which was considered to be adequate for the provision of visual feedback during training, but not sufficiently accurate for a reliable quantification of the efficacy of the training programme). The actuator was locked off for knee flexion such that the knee was returned to 90 degrees flexion with no opposing resistance.

Performance measurements: pre- and post-training Isometric leg strength. Leg strength was determined as the maximum voluntary isometric force generated by the knee extensors, with both hip and knee joints flexed at 90°. The apparatus used was similar to that described by Maughan et al. (1983). The subject was restrained by means of an adjustable seat belt fastened

24.3 (1.3) 25.5 (11.3) 21.3 (1.8) 21.2 (3.1) 22.3 (4.9) 18.5 (0.7)

No training 6 sets of:a 25 maximal repetitions (20-25 s) right leg 30 s rest (both legs) 25 maximal repetitions (20-25 s) left leg 30 s rest (both legs) 3 days'week -1 for 16 weeks b (48 sessions) 5 sets of: a 15 maximal repetitions (25-30 s) right leg 40 s rest (both legs) 15 maximal repetitions (25-30 s) left leg 40 s rest (both legs) 3 days.week -1 for 16 weeks b (48 sessions)

a The total number of repetitions/session performed by group TF was twice that of group TS, in an attempt to maintain approximately the same total work output for each group (the work done during a maximal leg extension at 4.19 rad.s -I is approximately half that performed at 1.05 rad.s-1; ROsier et al. 1986) b The 16-week training period was unavoidably interrupted by two 3-week periods of student vacations which occurred after 2 and 12 weeks of training

across the chest and hips to prevent the tendency of the hip joint to extend when the quadriceps contracted. The maximum reproducible force which could be sustained for 1-2 s was recorded at ankle level (36 cm from the knee joint) with a high precision load cell, amplified via a high gain strain gauge amplifier and displayed on a pen recorder. This force was taken to be the MVC, measured in newtons (N)).

Power output. The Wpe~kand Vp,p~.kwere determined during the performance of a series of 6-s ail-out sprints on a Monark 864 mechanically braked bicycle ergometer. The test began with the subject pedalling steadily at 90W (at a pedal velocity of 60 rev.min -1 with a resistive load of 15 N). After a count-down, the full load (see below) was introduced and the subject pedalled with an all-out effort until instructed to stop. The test was carried out on a daily basis, each day using one of six randomly assigned resistive loads expressed in relation to quadriceps MVC (9, 10, 11, 12, 13 and 14°70MVC). The absolute loads employed in the tests were unchanged pre- to post-training. Flywheel velocity was deter-

372 mined by a photo-optic sensor, capable of resolving every 0.05-rad turn of the flywheel, interfaced to a microcomputer (Acorn, BBC). Sampling was carried out at 25 Hz. Corrected power [i.e. with the inertial properties and acceleration/deceleration of the flywheel taken into account (Coleman et al. 1986)] was calculated over 1-s periods. The Wpoak(W) and vp,peak (rev'min -~) were taken as the highest respective 1-s values.

Table 3. Training effects on mean (SD) values for maximal voluntary contraction of the quadriceps

Habituation. Subjects were fully habituated to all the performance

Control (n = 10) (C) 550 (276) 570 (265) Training at 4.19rad-s -1 (n= 13) (TF) 583 (166) 643 (184) Training at 1.05 fad's -1 (n= 10) (TS) 598 (181) 631 (150)

tests prior to assessment and the commencement of training. This involved the performance of up to five MVCs of the knee extensors on each of 3-4 days, then three to four sprint cycle tests (each on a separate day) against a resistive load of 10% MVC. The performance measures from the final two habituation trials were analysed for their reproducibility [one-way ANOVA with repeated measures followed by determination of the reliability (intraclass correlation) coefficient, R (Safrit 1981)]. The value of R was extremely high for each performance variable: quadriceps MVC, R = 0.99; sprint cycle Wpe~k,R = 0.99; sprint cycle vp,pea~,R = 0.95.

Statistics Results are expressed as arithmetic mean (SD). The training study data were analysed using multivariate analysis of variance [training group (C, TF and TS) x trial (pre and post 16 weeks) with repeated measures on the latter factor]. Contrasts were carried out (1) between the response, after the 16 weeks, of the control group vs the two training groups (C vs TF and TS) and (2) between the response of the two training groups (TF vs TS). The MANOVA of the training data for the sprint cycle tests aiso included trend analysis of the relationship between the criterion performance measure [e.g. Wpe~kand the test load (9-14o70 MVC)]. Changes in these relationships after training were analysed by means of contrasts between the groups, in the pre- and post-training linear or quadratic trends. In this way, any load-specific changes in Wpo~kor Vp,peak could be identified. Analysis of covariance (Snedecor and Cochran 1980) was used to evaluate the significance of differences in the slope and elevation of the linear regression of Wpeakon MVC, pre- and post-training. Significance was accepted at the 0.05 level.

Results

Isometric exercise test T h e effects o f 16 weeks isokinetic t r a i n i n g o f the knee extensors o n the M V C o f the q u a d r i c e p s are s h o w n in T a b l e 3. A f t e r 16 weeks, a significant increase in the q u a d r i c e p s M V C o f all three g r o u p s t o g e t h e r was observed ( P = 0.022) b u t the g r o u p x t r a i n i n g i n t e r a c t i o n was n o t significant ( P = 0.167). Thus, a l t h o u g h M V C increased b y 8 . 1 % in t h e t r a i n i n g g r o u p s , the i m p r o v e m e n t was n o t significant c o m p a r e d with the c o n t r o l g r o u p r e s p o n s e ( m e a n increase 3.6O7o). M e n a n d w o m e n s h o w e d a similar p e r c e n t a g e increase in M V C p o s t - t r a i n ing (6o7o a n d 8O7o, respectively).

Dynamic exercise tests T h e effects o f 16 weeks isokinetic t r a i n i n g on cycle Wp~k a n d vp, peak are s h o w n in T a b l e 4, where the values f o r each p e r f o r m a n c e v a r i a b l e r e p r e s e n t the average over the entire l o a d range (9-14O7o M V C ) . T h e increases

Maximum voluntary contraction (N) Pre

Both training groups

Post

590 (169) 638 (166)

Significance of group mean training interaction (P value)

0.167

Table 4. Effects of training on variables derived from sprint cycle tests

Peak power Peak pedal output velocity (W. kg (rev. m i n - 1) BM - ~) Pre Control (C) (n = 6) a Training at (TF) 240°.s -1 (n= 11) a Training at (TS) 60°.s -x (n=9) a Significance of training response b (P value)

Mean SD Mean SD Mean SD

Post

11.6 11.5 2.0 2.0 13.3 14.3 1.8 1.8 14.3 15.3 3.1 3.2 0.018

Pre

Post

123.0 122.6 10.2 9.3 125.5 133.0 11.9 10.9 1 2 5 . 7 132.2 12.3 13.1 0.008

Values are means of the group mean and SD at each resistive load a n values reduced because not all subjects successfully completed the post-training tests over the full load range b Significance of training response of both training groups (TF and TS) compared with control group response There was no significant difference between the training response of TF and TS for peak power output (P=0.912) or peak pedal velocity (P = 0.721)

in Wpeak a n d Vp,peak d i s p l a y e d b y the t r a i n i n g g r o u p s were significantly d i f f e r e n t f r o m the c o n t r o l g r o u p response over the s a m e 16-week p e r i o d (Wpeak, P = 0.018 a n d Vp,peak, P~-- 0.008, respectively). T h e r e was n o significant d i f f e r e n c e b e t w e e n the t r a i n i n g r e s p o n s e o f g r o u p s T F a n d TS f o r either Wpeak ( P = 0 . 9 1 2 ) or vp,p~k ( P = 0 . 7 2 1 ) . T h e t r e n d s describing the r e l a t i o n s h i p between the resistive l o a d a p p l i e d a n d (i) Wpeak ( q u a d r a t i c ) a n d (ii) P P V (linear) r e m a i n e d u n a l t e r e d in all g r o u p s a f t e r the 16-week p e r i o d [ P = 0 . 4 6 9 (Wp~k) a n d P = 0 . 7 6 8 (Vp,peak); Fig. 1]. Thus, the t r a i n i n g - i n d u c e d increases in p e r f o r m a n c e were consistent across the l o a d r a n g e a p p l i e d , effecting a p a r a l l e l shift in the r e l a t i o n ships (see Fig. 1).

373 pre, 1~S 14.5

post-16 weeks, Wp~ak(W) = 198.3 + 1.255 MVC (N) (r = 0.97; SEE = 90.4)

[ i 13.5 ,,

After 16 weeks, the mean change in MVC in the control group was + 20 N (Table 3). With a regression coefficient of 1.208 (see above equation), this should have been associated with an increase in mean Wpeak of 24 W; the observed change was a 13 W decrease.

13 i

Wp~ak (W) = 264.1 + 1.208 MVC (N) (r= 0.96; SEE = 105.2)

12.5 12,

A

~ 11.3.

--

I

•

A

1

~2.5 13

~3.S 14

11

O

8.3

O.S

I0

10.S

~ H . S 12 I.OAO f'~ M V ~

14.5 l S

Discussion

15

[ :: 12

I.|

-~

1

0 II

8

10

~ 11 12 I,OAO 4"J,,fk~'¢l

13

14

lS

Fig. 1. Relationship between resistive load [% quadriceps maximum voluntary contraction (MVC)] and a peak power output and b peak pedal velocity during sprint cycling, pre (open symbols) and post (closed symbols) 16 weeks training (triangles, control group; circles, training group). Standard deviations (between 10 and 20°7oof the mean) omitted for clarity

Relationship between M V C and Wpeak Training groups. Pre-training (both training groups), there was a significant positive relationship between MVC and Wpeak (average Wpeak over the load range) (r=0.86, P0.05): pre-training,

Wp~ak(W) -- 211.2 + 1.326 MVC (N) (r=0.86; SEE= 116.5) post-training, Wp~ak(W) -- 211.6 + 1.344 MVC (N) (r= 0.82; SEE = 148.9) From the pre-training regression equation (regression coefficient= 1.326), an increase in MVC of 48N (the post-training increase; Table 3) would be expected to cause an increase in Wp~ak of 64 W. The actual increase observed, was not dissimilar from the predicted value of 71W.

Control group. Again, a significant positive relationship between MVC and Wpeak was observed (r=0.96, P < 0.0001), with no significant difference pre and post, in either the slope or the elevation of the linear regression equation (P>0.05):

The present study was carried out to investigate the effects of 16 weeks of isokinetic training of the knee extensors on the isometric strength of the same muscle group, and on dynamic power output during the performance of an activity requiring extensive utilisation of the knee extensors. Training elicited an 8.1%o increase in the quadriceps MVC, but the response of the training groups was not significantly greater than that of the controls (increase 3.6%). Previous training studies, of 12-24 weeks duration, in which the training movement (isotonic, concentric) was dissociated from the assessment task (isometric), have demonstrated significant improvements in quadriceps MVC of up to 20% (Hakkinen and Komi 1986; Rutherford and Jones 1986; Rutherford et al. 1986). However, no control group was included in the latter studies. The importance of including a control group in training experiments, particularly when dealing with active individuals, has previously been emphasised (Dons et al. 1979). In the studies of Hakkinen and Komi (1986), Rutherford and Jones (1986), and Rutherford et al. (1986), the training schedules placed a greater emphasis on the development of absolute strength, as evidenced by the fewer repetitions per set (6 and 1-10 respectively) and the heavier loads employed [80% and >70% 1RM respectively where IRM is the maximum load that can be lifted just once without a rest]. The present study was not solely directed towards the development of strength, and although a maximal effort was made during each leg extension, the peak torque which could be generated was limited by the preset velocity. Maximum torque generated at 105 rad-s -] and 4.19 fad's -1 is typically about 70% and 50%, respectively, of maximum isometric torque (Caiozzo et al. 1981) and declines throughout the training session as the muscle fatigues. Young et al. (1985) have suggested that it may be the level of neural drive during training, rather than the size of the load, that represents the stimulus for increasing strength. However, the results of the present study would appear to support, in contrast, the same authors' earlier conclusion (derived from a thorough examination of the literature on strength training) that at training loads below approximately 66% of maximum, no increase in MVC is observed even if up to 150 contractions, d a y - 1 are used (McDonagh and Davies 1984). If the major determinant of the adaptive response in terms of strength is, indeed, the tension generated by the muscle during training

374 (Goldberg et al. 1975), then this may explain the lower increases in MVC observed in the present study. In the dynamic exercise test a 5 - 8 % increase in Wpeak was observed pre- to post-training, which was significantly different f r o m the control group response (1% decrease). This is in contrast to the study of Rutherford et al. (1986) where, even though greater increases in MVC were observed, there was no significant increase in the Wpeakduring isokinetic cycling. Although the latter study may not have been specifically designed for the development of power, an increase would have been expected, consequent to the increase in quadriceps strength. Indeed, following their own pre-training regression equation of Wpeak on MVC [which had a regression coefficient (slope) of 1.2], the mean traininginduced increase in MVC in the men (111 N) should have been associated with a mean increase in Wpeak of approximately 133 W; an increase of just 24 W was observed. This tends to suggest that either the observed increases in MVC were accompanied by similar decreases in the maximal contraction velocity of the muscle (resulting in no change in power, the product of force and velocity), or that the increases in MVC, whilst significant, did not represent functional changes within the muscle such as an increase in the contractile material cross-sectional area. In the present study, the traininginduced increase in Wp~k was slightly greater than would have been predicted from the increase in MVC. Further, if the post-training increase in MVC did not represent a true change in the strength of the muscle (as intimated f r o m the control group response), then the adaptation in Wpeakis underestimated. This tends to suggest that true qualitative changes may have occurred within the muscle (rather than just neural changes, beneficial only to the training manoeuvre) possibly in the direction of accelerated contractile kinetics. A previous study which employed both isometric and dynamic training of the adductor pollicis muscle reported that, compared with isometric training, dynamic training produced less of an improvement in m a x i m u m tension, but a significantly greater increase in the calculated maximal velocity of shortening and the rate of tension development/relaxation of the muscle (Duchateau and Hainaut 1984). Such training-induced changes can be expected to be dependent upon an increase in myosin adenosine triphosphatase activity a n d / o r calcium ion movements (Duchateau and Hainaut 1984), although the involvement of these adaptations, with regard to the present study, can only remain speculative. Likewise, whether the similarity in the response of the two groups training at differing angular velocities was the result of identical modifications within the muscle, or merely represented the same outcome f r o m separate adaptations, remains to be investigated. In summary, it has been shown that 16 weeks of isokinetic training of the knee extensors resulted in no significant change in MVC, but produced a significant increase in the Vp,peak and Wpeakachieved during sprint cycling. The data therefore suggest that this type of training m a y be able to induce changes within the muscle that are beneficial to the performance of other tasks which

employ the trained muscle group at a similar work intensity but in a different pattern of co-ordination f r o m the training manoeuvre.

Acknowledgement. The support of the Sports Council of Great Britain is gratefully acknowledged.

References Caiozzo VJ, Perrine J J, Edgerton VR (1981) Training induced alterations of the in vivo force-velocity relationship of human muscle. J Appl Physiol 51:750-754 Coleman S, Hale T, Hamley EJ (1986) Correct power measurement in the Wingate Test. In: Reilly T, Watkins J, Borms J (eds) Proceedings of the VIII Commonwealth and International Conference, Kinanthropometry III. Spon, London, pp 308309 Coyle EF, Feiring DC, Rotkis JC, Cote III, Roby FB, Lee W, Wilmore JH (1981) Specificity of power improvements through slow and fast isokinetic training. J Appl Physiol Respit Environ Exerc Physiol 51 : 1437-1442 Dons B, Bollerup K, Bonde-Petersen F, Hancke S (1979) The effect of weight-lifting exercise related to muscle fiber composition and muscle cross-sectional area in humans. Eur J Appl Physiol 40: 95-106 Duchateau J, Hainaut K (1984) Isometric or dynamic training: differential effects on mechanical properties of a human muscle. J Appl Physiol Respir Environ Exerc Physiol 56:296-301 Ewing JL, Wolfe DR, Rogers MA, Amundson ML, Stull GA (1990) Effects of velocity of isokinetic training on strength, power and quadriceps muscle fibre characteristics. Eur J Appl Physiol 61 : 159-162 Goldberg AL, Etlinger JD, Goldspink DF, Jablecki C (1975) Mechanism of work-induced hypertrophy of skeletal muscle. Med Sci Sports Exerc 7:248-261 Hainaut K, Duchateau J (1989) Muscle fatigue, effects of training and disuse. Muscle Nerve 12: 660-669 Hakkinen K, Komi P (1986) Training-induced changes in neuromuscular performance under voluntary and reflex conditions. Eur J Appl Physiol 55 : 147-155 Jones DA, Rutherford OM, Parker DF (1989) Physiological changes in skeletal muscle as a result of strength training. Q J Exp Physiol 74:233-256 Kanehisa H, Miyashita M (1983) Effect of isometric and isokinetic muscle training on static strength and dynamic power. Eur J Appl Physiol 50: 365-371 Komi PV (1986) Training of muscle strength and power. Interaction of neuromotoric, hypertrophic and mechanical factors. Int J Sports Med 7:10-15 MacDougall JD, Ward GR, Sale DG, Sutton JR (1977) Biochemical adaptation of human skeletal muscle to heavy resistance training and immobilisation. J Appl Physiol 43 : 700-703 Maughan RJ, Watson JS, Weir J (1983) Strength and cross-sectional area of human skeletal muscle. J Physiol (Lond) 338: 37-49 McDonagh MJN, Davies CTM (1984) Adaptive response of mammalian skeletal muscle to exercise with high loads. Eur J Appl Physiol 52: 139-155 Narici MV, Roi GS, Landoni L, Minetti AE, Cerretelli P (1989) Changes in force, cross-sectional area and neural activation during strength training and detraining of the human quadriceps. Eur J Appl Physiol 59:310-319 Osternig LR (1986) Isokinetic dynamometry: implications for muscle testing and rehabilitation. Exerc Sport Sci Rev 14:4580

375 Petersen S, Wessel J, Bagnall K, Wilkins H, Quinney A, Wenger H (1990) Influence of concentric resistance training on concentric and eccentric strength. Arch Phys Med Rehabil 71:101105 ROsler K, Conley KE, Howald H, Gerber C, Hoppeler H (1986) Specificity of leg power changes to velocities used in bicycle endurance training. J Appl Physiol 61:30-36 Rutherford OM, Jones DA (1986) The role of learning and coordination in strength training. Eur J Appl Physiol 55:100105

Rutherford OM, Greig CA, Sargeant A J, Jones DA (1986) Strength training and power output: transference effects in the human quadriceps muscle. J Sports Sci 4:101-107 Safrit M (1981) Evaluation in physical education, 2nd edn. Prentice Hall, Englewood Cliffs, N. J. Snedecor GW, Cochran WG (1980) Statistical methods, 7th edn. Iowa Press, Ames, Iowa Young K, McDonagh MJN, Davies CTM (1985) The effects of two forms of isometric training on the mechanical properties of the triceps surae in man. Pfliigers Arch 405:384-388