Muscle tenderness and peak torque changes after ...

Jour nal of Sports Sciences , 1996, 14 , 291-299

M uscle tenderness and peak torque changes after downhill running following a prior bout of isokinetic eccentric exercise RO G E R G . E STO N , 1* SU E F IN N E Y, 2 ST E V E BA K E R 1 and VA SIL IO S BA LT Z O PO U L O S 3 1

Division of H ealth and Hum an Perfor m ance, U niversity of Wales, Victor ia Drive, B angor, G wyned d LL57 2EN, Departm ent of M ovem ent Science and Physical E ducation, University of Liver pool, PO B ox 147, Liver pool L 69 3B X and 3D ivision of Sport Science , C rewe + Alsager Faculty, The M anchester M etropolitan University, A lsager ST7 2H L, U K 2

Accepted 7 January 1996

Unaccustomed exercise (usually of an eccentric nature) is often followed by delayed onset muscle soreness (DOM S). Previous studies have found that prior eccentric activity produces a training effect which reduces DO MS and morphological changes. The aim of this study was to exam ine the effects of a prior bout of maximal isokinetic eccentric exercise on DOM S, strength loss and plasma creatine kinase (CK) changes following a downhill run. Ten male subjects with a mean (± S. D.) age of 22.5 ± 2.8 years, body mass of 62.67 ± 0.05 kg and height of 176 ± 3 cm were allocated to either a treatment group or a control group. The treatment group performed 100 maximal eccentric activations of the knee extensors in the dominant leg at 0.52 rad s-1 . Two weeks later, the downhill run was performed on a motor-driven treadmill. This consisted of ® ve bouts of 8 min at a gradient of -10% at a speed corresponding to 80% of the predicted maximal heart rate. The untrained group performed the downhill run as above but without the prior isokinetic session. Tenderness measurements, plasma CK activity and concentric and eccentric isokinetic peak torque measurements of the knee extensors at 0.52 and 2.83 rad s-1 were recorded prior to, immediately following and 2, 4 and 7 days after each protocol. The isokinetic protocol caused an increase (P < 0.01) in CK and tenderness and a decrease (P < 0.05) in concentric and eccentric torque at both speeds in the treatment group. Following the downhill run, a reduction in peak torque (P < 0.01) was observed in the eccentric and concentric modes at both isokinetic speeds in the control group. For the treatment group, the decrease in peak torque occurred only at the faster eccentric speed. With the exception of the faster eccentric speed, the decrement in peak torque was greater in the control group in all post-exercise isokinetic strength tests. There was less tenderness (P < 0.01) in the trained knee extensor muscle group. Peak torque also returned to pre-downhill values earlier for the trained group. Although plasma CK activity increased in both groups after downhill running, it was much lower (P < 0.01) in the trained group. The results suggest that a prior bout of isokinetic eccentric training reduces muscle damage, reduces the amount of strength loss and decreases the sensation of DO MS after downhill running. K eywords : Delayed onset muscle tenderness.

soreness, downhill running, isokinetic eccentric training,

Introduction Exercise that contains a large eccentric component, in which the muscle lengthens during activation, often induces delayed onset m uscle soreness (DO M S), which is ® rst felt after about 10 h and peaks between 24 and

* Author to whom all correspondence should be addressed. 0264-0414/ 96

©1996 E. & F.N. Spon

muscle

48 h. The soreness is typically accom panied by m uscle stiffness, pain on active m ovem ent, reduced ¯ exibility and tenderness when palp ated (Edwards et al., 1981; N ewham et al., 1983a; F riden et al., 1983a; Byrnes et al., 1985) and usually subsides within 5 days of the exercise. D ecrem ents in muscle strength occur im m ediately and last for several days following a bout of eccentric exercise (Davies and W hite, 1981; N ewham et al., 1988; Clarkson et al., 1992; Cleak and Eston,

Eston et al.

292 1992a). Associated w ith D O M S, there is evidence of in¯ am m ation and dam age to the affe cted m uscles, with elevated serum activities of speci® c enzym es such as creatine kinase (C K) (Friden et al., 1983a; N ewham et al., 1983b, 1986; Byrnes et al., 1985; Jones et al., 1986; N osak a et al., 1991; Eston et al., 1995). Studies have shown that a prior bout of eccentric training reduces the severity of D O MS after a repeated bout of eccentric work (Byrnes et al., 1985; Jones and N ewham, 1986; Pierrynowski et al., 1987). D uring the repair process, an adaptation takes place which m akes the m uscle m ore resistant to dam age and reduces the strength loss, soreness and elevated CK activity which are com m only observed after a bout of eccentric exercise (C larkson et al., 1987; Clarkso n and Tremblay, 1988; D onnelly et al., 1992). The effects m ay last up to 6 weeks (Byrnes et al., 1985; N osaka et al., 1991), although some studies have shown a much longer-lasting effect for C K (Nosaka et al., 1991; C larkson et al., 1992). A variety of m ethods of inducing m uscle soreness have been employed in previous studies (Cleak and Eston, 1992b), including active eccentric isokinetic dynam om etry procedures (Donnelly et al., 1992; Saxton et al., 1994; Crenshaw et al., 1994, 1995), although no study has used this m ethod prior to a bout of downhill running. Active isokinetic dynam ometers elicit eccentric activations by app lying force in the opposite direction to the concentric action of the m uscle. For exam ple, knee ¯ exion is induced while the subject attempts to extend the knee in the sitting position. T his generates an eccentric action of the knee extensors. However, the length of the activated muscles and the forces exerted during eccentric dynam om etry are different compared with other m odes of eccentric exercise, in particular downhill running. T here is a well-docum ented length-dependent com ponent in m uscle dam age (Newham et al., 1988). However, the physiological changes which result from eccentric training and prevent the recurrence of D O MS are unknown. Ebbeling and C larkson (1990) suggested that the m uscle repairs itself after the ® rst bout of dam age-inducing exercise and that adaptations within the m uscle-surrounding connective tissue were the reasons for the rapid training effect after the eccentric exercise bout. However, Clarkson et al. (1992) have since suggested that this theory is unlikely, as over a time period of 6 m onths, with the constant turnover of cellular com ponents, the `conditioned’ ® bres are unlikely to retain their adaptations. They hypo thesized that the ® rst bout of eccentric exercise adapts the m otor-unit recruitment pattern over the m ovem ent range, to m ore equally distribute the force between the m uscle ® bres, and consequently reduces the chance of severe dam age to any one motor unit. As m otor skills

are `stored’ for a long period of time, the neurological response (as well as the m orphological changes) m ay account for the long-term training effect w hich protects the m uscle from further damage. However, it is unclear w hether this phenom enon would occur when the m ovem ent pattern and m ode of eccentric exercise are unrelated to the subsequent eccentric bout. In this respect, the m ode of eccentric activation of the knee extensors during isokinetic dynamom etry and dow nhill running are very different. T he m uscles are not at full length in isokinetic work in the seated position and the torque imposed accom modates for m axim al loading of the knee extensors throughout the joint range of m otion. T hus, the aim of this study was to determ ine if a prior bout of m axim al isokinetic eccentric exercise could provide protection against the sym ptom s of m uscle dam age (m uscle tenderness, strength loss, increased plasm a CK activity) resulting from a bout of dow nhill running.

M ethod Ten healthy m ale sports science students, with no prior experience of either the isokinetic eccentric training protocol or the interm ittent downhill run protocol, were random ly allocated to either a treatm ent group (n = 5) (m ean ± S. D.: age 23.2 ± 2.9 years, height 175 ± 4 cm, m ass 72.1 ± 1.8 kg) or a control group (n = 5) (age 21.8 ± 2.9 years, height 17 6 ± 3 cm, m ass 73.2 ± 2.2 kg). Independent groups t-tests revealed no signi® cant differences in the age, height and body mass of the two groups. M easures of m uscle tenderness, isokinetic eccentric and concentric knee extensor peak torque values at two angular velocities (0.52 and 2.83 rad s-1 ) were m easured in the dom inant leg. Plasm a CK activity was m easured im m ediately before and after each protocol, and 2, 4 and 7 days later. M uscle tender ness M uscle tenderness was evaluated using a myometer (Penny and Giles Transducer, Christchurch, UK) with the subject in the supine position. Following the m ethod of N ewham et al. (1983a), the transducer was app lied sequentially at the proxim al, m id and distal m uscle sites of the anterior thigh (following the line of the rectus fem oris) with a force of up to 40 N. T he subject was ask ed to report the instant pain was perceived. If no pain was reported, it was assum ed that there was no tenderness. The reading from the myom eter was then deducted from the ceiling value of 40 N and this was considered as the tenderness value. Tenderness values from the three sites were then added

293

Isokinetic eccentr ic training and downhill r unning together to represent overall m uscle tenderness of the knee extensors. We have used this m ethod successfully in previous studies to differentiate pain levels between m uscle groups after downhill running and to evaluate m uscle soreness after eccentric exercise (Eston et al., 1994, 1995, 1996). Creatine kinase activity Plasma CK activity was determ ined from a ® ngertip blood sam ple. A warm ® ngertip was cleaned w ith a sterile alcohol swab and allowed to dry. Capillar y puncture was m ade with an Autoclix lancette and a sam ple of whole fresh blood (32 l l) was pipetted from a capillary tube onto the test strip and analysed for C K activity via a colorom etric assay procedure (Re¯ otron, Boehringer M annheim, Lewes, U K). This system uses a plasm a separation principle w hich is incorporated in the reagent carrier on the test strip. Peak torque of the knee extensors Peak torque of the knee extensors (quadriceps m uscle group) was evaluated on the dom inant leg using a Biodex II dynamom eter (Biodex M edical System s, Shirley, N Y). T he tests included both concentric and eccentric isokinetic m axim al torque m easurem ents at angular velocities of 0.52 and 2.83 rad s-1 . The subjects were seated on the Biodex chair with the back rest at an angle of 1.8 rad and the pelvis, chest and involved thigh secured with app ropriate straps to prevent extraneous m ovem ent. A fam iliarization and warm-up period was given prior to the test consisting of two to three subm axim al and one m axim al repetition at both speeds in the concentric and eccentric modes. T he axis of rotation of the dynam om eter was aligned with the m ost prom inent point of the lateral fem oral condyle. The pad of the lever arm was positioned at a distal point on the tibia near the m alleoli. T his position was adopted because it allows m axim um activation and is usual practice in m ost studies exam ining m aximum isokinetic function in subjects without joint injury (Siewert et al., 1975; Taylor and Casey, 1986; D vir, 1995). The range of m ovem ent (RO M) for all sessions was set for each individual so as to allow the m uscle to work at its m axim al RO M . The RO M for all tests was from approxim ately 0.17 rad to 1.57 rad of knee ¯ exion. T he testing protocol consisted of ® ve maxim al repetitions, from which the highest torque value was recorded. The tests were com pletely random ized and rest periods of 5 m in were allowed between tests. All subjects were given standardized instructions to work as hard and fast as possible against the resistance of the dynam om eter and aim to im prove the torque graphs from the previous repetitions. T he dynam om eter torque was displayed on

the computer m onitor in real-tim e for feedback and m otivation purposes. This procedure was followed because visual feedback can im prove m axim um m uscular torque during isokinetic tests (Baltzopoulos et al., 1991). The weight of the exercising leg was m easured for gravity correction. As the m uscles m ust be relaxed during the gravity correction, we used an angle of 0.52 rad (30¡ knee ¯ exion) in order to avoid any unwanted contribution from the ham string. This was adopted because it is dif® cult to relax in the full extension position. Isokinetic eccentric exercise protocol Two weeks prior to the downhill run, the treatment group perform ed 100 continuous m axim al voluntar y eccentric activations at 0.58 rad s-1 . T he subjects were positioned as previously described for m easurem ent of peak torque. T he activations were perform ed as one set w ith no rest allowed. T he subjects were encouraged to attain the highest score, which was aided by instantaneous visual display of the peak torque curves on the com puter m onitor. Verbal feedback was also given to elicit m axim al effor t. D ownhill run protocol T he treatm ent group and the control group each perform ed an interm ittent downhill run protocol, as used in previous studies (Eston et al., 1994, 1995). This consisted of a 40 m in interm ittent bout of 5 ´ 8 m in on a -10% incline on a m otor-driven treadm ill, w ith 2 m in standing rest between each bout. The speed of the treadm ill was set to elicit 80% of the age-predicted m axim um heart rate (220 - age; ACSM , 1991). Heart rate was constantly m onitored using a Polar Sport Tester (Polar Electro, Kempele, Finland). At the end of each 8 m in bout, heart rate and treadm ill speed were recorded. Treatm ent of data For the treatm ent group, the effects of the isokinetic protocol on plasm a CK , peak torque and m uscle tenderness were analysed by a one-way, repeated-m easures analysis of variance to com pare differences between m easurements imm ediately before and after, and 2, 4 and 7 days after the isokinetic eccentric exercise protocol. W hen there was a signi® cant m ain effect, the posthoc Tukey procedure was applied to determ ine w here the signi® cant differences lay. W ith the exception of the m uscle tenderness data, w here pre-test values were 0, comparisons between the treatment and control groups were analysed by a twofactor (time vs treatment group) analysis of covariance

Eston et al.

294 (AN COVA). T his was done to control for any initial differences between the two groups w hich m ay have confounded the post-test differences between the two groups. Follow -up post-hoc Tukey tests were app lied to the adjusted m ean scores if the analysis of varian ce procedure indicated a signi® cant m ain effect or interaction.

R esults Responses of the treatment group to the isokinetic protocol Responses to the m axim al eccentric isokinetic protocol by the treatm ent group are show n in Tables 1 and 2. One-way repeated-m easures AN OVA revealed a signi® cant m ain effect for time for each of the dependent variab les of plasm a C K activity, tenderness and peak torque. Creatine kinase activity Plasma CK activity increased signi® cantly (P < 0.01) from baseline values (267% ) by day 2 and reached a peak of 371% of baseline values by day 4. By day 7, the CK values had returned to norm al (Table 1). M uscle tender ness Tenderness increased signi® cantly (P < 0.01) from baseline values by day 2 and decreased signi® cantly by day 4, although the latter value still rem ained higher than baseline values. By day 7, the values had returned to baseline (Table 1). Peak torque There was an im m ediate post-exercise loss in peak torque (P < 0.01) for both concentric and

eccentric m odes at the slow and fast angular velocities. D ecrements ranged from 10 to 23% by day 2 and lasted for at least 2 days. By day 7, however, the values had returned to baseline levels. C om parison of treatment versus control g roup C reatine kinase activity A two-fac tor analysis of covariance revealed a signi® cant m ain effect for time (F 2,16 = 24.0, P < 0.01), no m ain effect for group (F 1,7 = 4.36, P = 0.07) and a signi® cant interaction of time 3 group (F 2,16 = 4.96, P < 0.05). T hus, although the plasm a C K activity increased in both groups after downhill running, the magnitude of change was m uch greater for the control group. T he peak values were 150 and 580% greater than baseline values for the treatm ent and control groups, respectively. Follow-up m ultiple-com pariso ns tests revealed that plasm a CK activity in the control group was signi® cantly higher on day 2 (602 ± 216 vs 125 ± 131 U l-1 ) and day 4 (534 ± 269 vs 295 ± 110 U l -1 ) (Fig. 1). M uscle tender ness Analysis of variance indicated a signi® cant main effect for time (F 2,16 = 97.4, P < 0.01) and group (F 1,7 = 15.1, P < 0.01). Tenderness increased across time in both groups. T here was also a signi® cant interaction of time ´ group (F 2,16 = 9.78, P < 0.01). Post-hoc follow -up tests revealed a disproportionate increase in m uscle tenderness in the control group on day 2 (41.0 ± 2.5 vs 21.4 ± 1.1 N ) and day 4 (17.2 ± 4.5 vs 5.6 ± 6.1 N ). By day 7, tenderness app roached baseline values (Fig. 2).

Table 1 Creatine kinase (CK) activity and tenderness after 100 maximal, isokinetic eccentric activations of the knee extensors in the treatment group (m ean ± S. D.)

Variable

Pre-test

CK (U l-1 ) Tenderness (N)

86 ± 22 0

a

Im mediately post-test

-

Day 2 316 ± 207 19.4 ± 4.2

0.60 ± 0.9

a a

Day 4

Day 7

405 ± 234 a 9.4 ± 1.7 a

120 ± 62 1.4 ± 0.5

F 3,12

6.77 84.2

P

< 0.01 < 0.01

Signi® cantly different from baseline (pre-test score).

Table 2 Concentric and eccentric maximal strength (peak torque) m easurements (N´m) at slow and fast speeds before, immediately after and several days after the eccentric isokinetic protocol in the treatment group

Mode Eccentric Eccentric Concentric Concentric a

Speed (rad s-1 ) 0.58 2.83 0.58 2.83

Pre-test 359 351 265 159

± 38.8 ± 32.5 ± 26.8 ± 19.6

Imm ediately post-test 323 270 215 135

Signi® cantly different from baseline (pre-test score).

± 26.9 ± 29.6 ± 18.9 ± 16.1

a a a a

Day 2 328 263 192 138

± 40.2 ± 49.2 ± 24.0 ± 24.3

Day 4 a a a

332 ± 322 236 155

53.2 ± 45.6 ± 27.2 ± 14.8

Day 7 356 ± 349 264 258

44.1 ± 38.0 ± 0.6 ± 18.7

F 4,16

4.66 27.16 13.94 4.54

P

< 0.05 < 0.01 < 0.01 < 0.05

Isokinetic eccentr ic training and downhill r unning

295

F igure 1 Comparison of creatine kinase activity (U l-1 ) in the treatment (h ) and control ( e ) groups pre-test and 2, 4 and 7 days after downhill running. The values are adjusted means (± S. E.) from analysis of covariance.

Peak torque Eccentric and concentric peak torque m easures at both slow (0.58 rad s-1 ) and fast (2.83 rad s-1 ) angular velocities are shown in Figs 3 and 4. T here were signi® cant m ain effects for time (P < 0.01) for the slow concentric (F 3,24 = 19.8) and slow eccentric (F 3,24 = 15.2) m odes and the fast concentric (F 3,24 = 14.5) and fast eccentric (F 3,24 = 6.3) m odes.

Post-hoc tests indicated that peak torque was signi® cantly lower (P < 0.01) than the pre-run baseline values for both groups im m ediately after the run, up to and including day 2. W ith the exception of the fast eccentric angular velocity (F 1,7 = 3.76, N. S.), there was also a signi® cant m ain effect for group. The overall m ean values of post-exercise peak torque measures for

F igure 2 Muscle tenderness (N) pre-test, immediately post-test and 2, 4 and 7 days after downhill running in the treatment (h ) and control (e ) groups.

296 the treatment group were greater than the control group at both slow (F 1,7 = 8.4, P < 0.05) and fast (F 1,7 = 62.7, P < 0.01) concentric angular velocities and the slow eccentric angular velocity (F 1,7 = 21.6, P < 0.01). The AN C OVA also revealed a signi® cant interaction of group ´ time at the slow eccentric angular velocity (F 3,24 = 4.3, P < 0.05) and the slow concentric angular velocity (F 3,24 = 6.6, P < 0.01). Post-h oc follow-up tests revealed a greater decrease in peak torque in the control group im m ediately following dow nhill running, which rem ained for at least 2 days. These differences can be seen quite clearly in Figs 3 and 4. By day 4 there were no differences in peak torque between the two groups and the values had returned to baseline by day 7.

D iscu ssion Although there was considerable variation in the severity of m uscle tenderness am ong subjects, w hich has been observed in previous studies (Clarkso n and Ebbeling, 1988; Trif¯ etti et al., 1988), the ® ndings suggest that a prior bout of isokinetic eccentric exercise provides som e degree of protection against further m uscle tenderness. The treatm ent group recorded signi® cantly lower tenderness values than the control group at day 2 and day 4. T he reduction in tenderness follow ing isokinetic training is sim ilar in m agnitude to that in a study by N ewham et al. (1987), although exact comparisons are dif® cult due to the difference in proto-

Eston et al. cols and soreness evaluation. Previous training which involves eccentric activation of the m uscle (as opposed to concentric activation) reduces the morphological changes, perform ance changes and creatine kinase activity in the blood (see reviews by Cleak and Eston, 1992a; Eston et al., 1995). Pierrynowski et al. (1987) suggested that speci® c eccentric movem ent training is required to cause the physiolo gical changes which prevent m uscle soreness and dam age occurring with subsequent eccentric work (in the form of downhill running). Although the sym ptoms of m uscle dam age were not com pletely prevented by the isokinetic protocol, the results from this study suggest that a protective effect did occur, which reduced the severity of the sym ptom s com monly associated with D OM S. T he ® ndings therefore suggest that a prior bout of eccentric training provides protection against m ore severe dam age in a subsequent activity w hich possesses different force-velocity characteristics. In agreem ent w ith m any previous studies, the individual changes in plasm a C K activity were highly variable (Newham et al., 1983b, 1988; Evans et al., 1986). Although direct com parisons are dif® cult, due to the differences in m ethods and protocol designs, the rise in plasm a C K activity after the isokinetic exercise in the treatment group was relatively low com pared to som e studies which have induced m uscle soreness in the knee extensors (e.g. Costill et al., 1990). However, the values in the present study were higher than those observed by H asso n et al. (1993) after a continuous bout of low-

F igure 3 Peak torque measurements (N´m ) at 0.58 rad s-1 pretest, immediately post-test and 2, 4 and 7 days after downhill running in the treatment and control groups. The values are adjusted means (± S. E.) from analysis of covariance. h , treatment eccentric; e , control eccentric; s , treatment concentric; n , control concentric. ¤ Control eccentric and control concentric signi® cantly different from baseline (pre-test score), P < 0.05. *Treatment eccentric and treatment concentric signi® cantly different from control at equivalent time phase, P < 0.05.

Isokinetic eccentr ic training and downhill r unning

297

F igure 4 Peak torque measurements (N´m ) at 2.83 rad s-1 pretest, immediately post-test and 2, 4 and 7 days after downhill running in the treatment and control groups. The values are adjusted means (± S. E.) from analysis of covariance. e , treatment eccentric; s , control eccentric; n , treatment concentric; h , control concentric. *Signi® cantly different from baseline, control concentric group. ¤ Signi® cantly different from baseline, treatment eccentric group. # Signi® cantly different from baseline, control eccentric group.

ering the body m ass plus 10% in a stepping protocol, which like the present study induced soreness in one leg only. It is possible that the relatively low plasm a CK activity values in the present study could be attributed to the repeated, continuous nature of the isokinetic protocol. T he onset of fatigue decreased the torque generation and reduced the severity of the m uscle dam age. N evertheless, despite the relatively low level of m uscle dam age (inferred from the low plasm a CK activity), the protocol was suf® cient to provide a protective effect to further m uscle dam age during the dow nhill run. After the downhill run, the rise in plasm a CK activity for the treatment group was greater than in other studies incorporating a prior bout of eccentric exercise (Newham et al., 1987; N osaka et al., 1991). This was probab ly because in the present study, the quadriceps group of m uscles from only one leg was trained prior to the run. D ownhill running uses a combination of m uscles that work eccentrically (e.g. hip extensors, ankle extensors and ¯ exors), w hich were not previously trained by the isokinetic protocol. Thus it is likely that damage would naturally be induced in these unprotected m uscles, resulting in enzym e release. N evertheless, post-exercise plasm a CK activity for the treatm ent group was lower than the control group at all post-dow nhill run times up to day 4, after which

plasm a CK levels returned to baseline levels in both groups. The differences in post-exercise plasm a CK activity between the two groups was larger than we anticipated, particularly as the other active m uscles used in downhill running would not be protected by the initial bout of eccentric exercise. Perhaps one explanation could be that a central effect is at work, which increases plasm a C K clearance rates. The results of this study suggest that a prior bout of isokinetic eccentric exercise at 0.58 rad s-1 leads to greater retention of eccentric and concentric peak torque following a bout of downhill running, particularly at relatively low angular velocities (0.58 rad s-1 ). W hen peak torque was m easured at the faster eccentric angular velocity (2.84 rad s-1 ), the decrement in peak torque was sim ilar in both groups. A possib le explanation could be that the training effect was m ediated by the speed of the prior bout of isokinetic training (0.58 rad s-1 ). Friden et al. (1983b) found that the rate of strength restoration, following eccentric activation, was slower for fast activation velocities. T he results of this study concur w ith that ® nding. By day 4, eccentric peak torque at 2.83 rad s-1 in the control group had still not returned to baseline values, despite returning to baseline values at the slower eccentric activation velocity. Friden et al. suggested that the muscle ® bres

298 responsible for the tension developm ent at higher angular velocities (type II ® bres) are m ore extensively dam aged than type I ® bres. This m ay explain the slower restoration of peak torque in the control group as eccentric exercise affects m ainly type II ® bres (Friden et al., 1983b) and it is m ore likely that type II ® bres were m ore extensively dam aged during the downhill run. C oncentric peak torque values in the treatment group were not affe cted by the dow nhill run, w hich provides further evidence to indicate that the dam age was m inim ized by the prior bout of eccentric exercise in this group. In conclusion, it would app ear that post-downhill run changes in plasm a CK activity, m uscle tenderness and peak torque in the knee extensors are reduced by a prior bout of isokinetic eccentric training. There was a notable difference in the time course for the recovery of peak torque and reduction in plasm a CK activity between the treatm ent and control subjects in this study. T he physio logical changes which result from eccentric training that reduce the aforem entioned effects are as yet unknown. It is acknow ledged that the sam ple size in this study was sm all and that this will have reduced the power of the statistical tests to reveal signi® cant differences. However, the fact that there were signi® cant changes in peak torque, m uscle tenderness and plasm a CK activity in the control group, and these changes were much m ore m arked than in the treatm ent group, suggest that the in¯ uence of the isokinetic treatm ent was suf® cient to provide a protective effect. Thus, the evidence presented here suggests a large treatm ent effect, despite the relatively low power of the study. N evertheless, one should not misapprehend the probability of a Type I error having occurred due to the sm all sam ple size. Further study is therefore recomm ended to assess the effects of non-speci® c eccentric training as a m eans of reducing the dam ag ing effects of subsequent bouts of eccentric exercise.

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