Knee angular displacement and extensor muscle activity in telemark ...

Journal of Sports Sciences, 2004, 22, 357–364

Knee angular displacement and extensor muscle activity in telemark skiing and in ski-specific strength exercises JOHNNY NILSSON1,2* and PER HAUGEN1 1

The Norwegian University of Sport and Physical Education, Oslo, Norway and 2University College of Physical Education and Sports, Stockholm, Sweden

Accepted 14 June 2003

Much of the training of competitive telemark skiers is performed as dry-land exercises. The specificity of these exercises is important for optimizing the training effect. Our aim here was to study the activation of the knee extensor musculature and knee angular displacement during competitive telemark skiing and during dry-land strength training exercises to determine the specificity of the latter. Specificity was analysed with respect to angular amplitude, angular velocity, muscle action and electromyographic (EMG) activity. Five male telemark skiers of national and international standard volunteered to participate in the study, which consisted of two parts: (1) skiing a telemark ski course and (2) specific dry-land strength training exercises for telemark skiing (telemark jumps and barbell squats). The angular displacement of the right knee joint was recorded with an electrogoniometer. A tape pressure sensor was used to measure pressure between the sole of the foot and the bottom of the right ski boot. Electromyographic activity in the right vastus lateralis was recorded with surface electrodes. The EMG activity recorded during maximum countermovement jumps was used to normalize the EMG activity during telemark skiing, telemark jumps and barbell squats. The results showed that knee angular displacement during telemark skiing and dry-land telemark jumps had four distinct phases: a flexion (F1) and extension (E1) phase during the thrust phase of the outside ski/leg in the turn/jump and a flexion (F2) and extension (E2) phase when the leg was on the inside of the turn/jump. The vastus lateralis muscle was activated during F1 and E1 in the thrust phase during telemark skiing and telemark jumps. The overall net knee angular amplitude was significantly greater (P50.05) for telemark jumps than for telemark skiing. Barbell squats showed a knee angular amplitude significantly greater than that in telemark skiing (P50.05). The mean knee angular velocity of the F1 and E1 phases during telemark skiing was about 0.47 rad × s71; during barbell squats, it was about 1.22 rad × s71. The angular velocity during telemark jumps was 2.34 and 1.59 rad × s71 in the F1 and E1 phase, respectively. The normalized activation level of the EMG bursts during telemark skiing, telemark jumps and barbell squats was 70–80%. In conclusion, the muscle action and level of activation in the vastus lateralis during the F1 and E1 phases were similar during telemark skiing and dry-land exercises. However, the dry-land exercises showed a larger knee extension and flexion amplitude and angular velocity compared with telemark skiing. It appears that an adjustment of knee angular velocity during barbell squats and an adjustment of knee angle amplitude during both telemark jumps and barbell squats will improve specificity during training. Keywords: dry-land exercise, electromyography, kinematics, telemark skiing.

Introduction Telemark skiing is a form of alpine skiing in which the ski boot is fixed in the ski binding at the toe only and the heel rises during ski turns. This allows a typical ‘telemark’ skiing style in which the inside leg ‘lags behind’ the outside leg in the turns. Since 1987, international ski races, including world championships, * Address all correspondence to Johnny Nilsson, University College of Physical Education and Sports, Box 56 26, S-114 86 Stockholm, Sweden. e-mail: [email protected]

have been held in this discipline. Telemark skiing equipment is similar to that used in other alpine ski race disciplines but with ski bindings fixed at the toe only and longer poles. Although telemark skiing is an original form of alpine skiing, there are few data pertaining to its physiological demands and biomechanical aspects. To our knowledge, no biomechanical data have been reported for telemark skiing or specific strength training exercises for this form of alpine skiing. Biomechanical data do exist for other forms of alpine skiing. Giant slalom is probably the form that most resembles competitive

Journal of Sports Sciences ISSN 0264-0414 print/ISSN 1466-447X online # 2004 Taylor & Francis Ltd DOI: 10.1080/02640410310001641557

358 telemark skiing in general appearance and movement cycle duration. In a study of this discipline, Berg et al. (1995) examined leg extensor muscle activity and hip and knee joint angular displacement. They showed that the giant slalom places heavy demands on leg extensor muscular strength, has a mean cycle duration of 3.0 s with load periods of up to about 1.5 s, and demands predominantly eccentric muscle action. Hintermeister et al. (1995) examined electromyographic (EMG) activity in the leg and trunk muscles during the slalom and giant slalom. They found, among other things, that the leg extensor muscles were highly activated during the thrust phase in the ski turn. There was also a surprising similarity in muscle activation between the slalom and giant slalom. Similarly, in an extensive study of ski instructors performing basic techniques in the Austrian ski teaching curricula, Mu¨ller (1994) reported the typical involvement of the leg extensors, including the quadriceps femoris. In telemark skiing, as in other alpine ski disciplines, athletes spend a substantial amount of time in dry-land strength training. For their optimal adaptation to alpine skiing, a large part of their strength training should be skiing-specific, in terms of muscle action and level of activation, as well as joint angular amplitude and angular velocity. Strength training is specific – that is, it develops strength characteristics related to muscle length and velocity of muscle action similar to those that have been trained. Previous studies have documented training specificity to type of contraction (Sale and MacDougall, 1981; Komi, 1986; Sale, 1988), joint angle (Thepaut-Mathieu et al., 1988) as well as velocity of resistance training (Lesmes, 1978; Caiozzo et al., 1981; Kanehisa and Miyashita, 1983). Recently, there has been an increasing interest in technique-specific training methods. Ground reaction forces normal to the ski or ski-boot and kinematics were investigated by Raschner et al. (1997) in simulation exercises for slalom and by Lindinger et al. (2001) in cross-country skiing. In a study of ski jumping, Schwameder et al. (1997) recorded electromyograms of the relevant musculature together with ground reaction forces. These studies provide valuable information about many parameters during ski-specific dry-land exercises. For telemark skiing, there have been no sport-specific evaluations of strength training exercises. The aims of this study were to examine knee angular displacement and extensor muscle activity during telemark skiing, and to evaluate strength training exercises for this form of skiing with respect to knee angular displacement and extensor muscle activity. We describe and analyse the activation of the vastus lateralis, an important knee extensor muscle in alpine skiing (Mu¨ller, 1994; Berg et al., 1995; Hintermeister et al., 1995).

Nilsson and Haugen Methods Participants Five skilled male telemark skiers, all of whom had represented the Norwegian national team and two of whom were world champions, volunteered to participate in the study. Their mean (+ s) age, height and body mass were 26+4 years, 1.85+0.06 m and 80+2 kg, respectively. Informed consent was obtained and the study procedures were approved by the Regional Ethics Committee of the Norwegian Research Council for Science and the Humanities. Apparatus and experimental design The study was done in two parts, during which the angular kinematics of the knee joint, the EMG activity of the vastus lateralis and the pressure under the sole of the foot were recorded during: (1) skiing a telemark ski course and (2) dry-land telemark skiing-specific strength training exercises. All measurements were performed on the right leg. A custom-made tape pressure sensor mounted in a detachable sole was used to measure pressure between the foot insole and the bottom of the right shoe or ski boot. The linearity and resolution of the tape pressure sensor was not accurate enough to allow quantification of forces in great detail, and therefore the sensor signals were only used as arbitrary data to detect the time periods when the participant applied force to the bottom of the ski boot or shoe. The angular displacement of the right knee joint was recorded using a custom-made lightweight linear electrogoniometer. The EMG activity in the vastus lateralis of the right leg was recorded with surface electrodes (Neuroline, type 72501-K, Medicotest A/S, Denmark) taped to the skin over the muscle belly. The electrogoniometer and pressure sensor were sampled at a rate of 125 Hz, and that of the electromyograms at 500 Hz. The signals were stored in a specially designed lightweight microprocessor carried by the participant. The sampled and stored data were later transferred to a computer for further analysis. The electrogoniometer was calibrated by recording two known angles (1808 and 908). To normalize the EMG activity in the subsequent telemark skiing, telemark jumps and barbell squats, peak EMG activity in the vastus lateralis was collected during three maximal countermovement jumps. A dynamic eccentric–concentric muscle action (i.e. countermovement jump) was selected for the calculation of peak EMG because of the specificity of EMG amplitude related to this type of contraction (Tesch et al., 1990; Seger and Thorstensson, 1994). Calibration of the electrogoniometer and

EMG and kinematics of telemark skiing and dry-land exercise normalization of the EMG activity was repeated before each part of the investigation. In the first part of the study, the participants skied a 186 m telemark course with nine open gates symmetrical in relation to the fall-line. The mean distance between the gates in the direction of the fall-line/course (including the start and the first gate) was 20.7+3.6 m. The slope was measured using a grade scale between each gate, with a mean slope of 17.9+1.58. The mean medio-lateral distance between the gates was 3.6 m. In the second part of the study, two dry-land exercises familiar to the participants were performed: 1. Telemark jumps were performed on a large treadmill (4.3 6 3.0 m; Refox, Sweden). A downhill slope of 158 was created by elevating the rear of the treadmill belt. The speed of the treadmill belt was set to 1.0 m × s71. The participants wore conventional athletic shoes and were instructed to perform downhill telemark jumps forwards and from side to side to

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lines 0.6 m to the left and right of the midline, maintaining a constant mean position on the treadmill. The participants performed several jumps but stopped exercising before they became fatigued. 2. Barbell squats (1- to 3-RM) were performed from a normal standing to a deep knee bend position (5908 knee angle) and back to normal standing. Data analysis The duration and amplitude of the EMG burst and knee angular displacement were measured by means of the cursor facilities of a computer program (Origin 5.0, Microcal Software Inc., MA, USA). The EMG and angular displacement values were calculated from one movement cycle during barbell squats and three movement cycles during telemark skiing and telemark jumps for each participant. The kinematic data were smoothed using 50 points adjacent point averaging (Fig. 1). The angular move-

Fig. 1. Raw recordings of foot sole pressure, knee angle and EMG activity in the right vastus lateralis (VL) for a representative participant during: (A) skiing a telemark course, (B) telemark jumps and (C) barbell squats. F = flexion phase and E = extension phase (for definition of F and E onsets and phases, see the Methods section).

360 ment cycle of the knee joint during telemark skiing and telemark jumps was divided into four phases (see Figs. 1A,B, 2A,B). The first flexion phase (F1) in the cycle was the flexion of the knee joint of the outside leg during the thrust phase in the ski turn or jump. The subsequent extension of the knee joint of the outside leg during the thrust phase was the first extension phase (E1). The F1 phase was defined as the eccentric phase and the E1 as the concentric phase of the action of the vastus lateralis. The corresponding phases in the cycle when the leg switched to become the inside leg in the

Nilsson and Haugen ski turn or telemark jump were termed the second flexion phase (F2) and the second extension phase (E2). The analysis of the angular movements of the knee joint during barbell squats was limited to the phases that corresponded to the highly mechanically loaded F1 and E1 phases during telemark skiing and telemark jumps. Thus, the angular movement cycle of the knee joint during barbell squats contains only two phases: flexion (F1) and extension (E1). The minimum and maximum of the knee angular displacement curve were marked with a cursor to distinguish the onset of

Fig. 2. Mean (+ s) knee angular displacement amplitude and normalized EMG activity temporal pattern of the vastus lateralis (VL) for the right leg in: (A) telemark skiing, (B) telemark jumps and (C) barbell squats. The picture above each figure shows the approximate position of the skier in relation to knee angular displacement and EMG activation periods. F = flexion phase and E = extension phase (for definition of F and E onsets and phases, see the Methods section).

EMG and kinematics of telemark skiing and dry-land exercise the different phases. When the minimum was elongated in time with a constant amplitude or small changes in amplitude, the middle position of the minimum was marked. The net knee angular displacement of a phase was defined as the difference between the onset of that phase and the onset of the next phase. The mean angular velocity of the different extension and flexion phases was calculated by dividing the net phase amplitude by the phase duration. The EMG of the vastus lateralis for barbell squats was analysed during the eccentric–concentric phase (F1 and E1 of the knee joint). The EMG signals were numerically full-waverectified, smoothed with adjacent point averaging (10 points) and normalized to the peak EMG activity during maximal countermovement jumps. The onset and offset of the eccentric and concentric EMG bursts were determined by visual inspection. The area under the EMG curve representing the eccentric and concentric muscle action was measured and the mean EMG was calculated by dividing the area by burst duration. Statistical analysis For statistical analysis, the StatView statistical package (Version 5.0, SAS Institute Inc., USA) was used. All data are reported as the mean+standard deviation (s). Differences between telemark skiing and strength training exercises were assessed using repeated measures analysis of variance (ANOVA) followed by a Scheffe´ post-hoc test. Statistical significance was set at P50.05.

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lateralis normalized to cycle duration in telemark skiing, telemark jumps and barbell squats. The knee angular amplitudes at the onset/offset of the flexion phases (F) and extension phases (E) are also shown. The yield at the knee joint during the mechanically loaded phases (F1 and E1) in telemark jumps and barbell squats was more pronounced and the overall angular amplitude was larger than in telemark skiing. The knee joint in telemark jumps and barbell squats was more extended at the onset of F1 at the start of the thrust phase and more flexed at the onset of E1 than in telemark skiing. The relative burst duration of the vastus lateralis in the normalized plots was similar for telemark skiing and telemark jumps, with activation periods mainly during the F1 and E1 as well as the E2 phases. During barbell squats, the vastus lateralis was constantly activated during the F1 and E1 phases. The F1 and E1 phases resemble eccentric and concentric muscle actions of the vastus lateralis, respectively. The differences in knee amplitude between the onset of F1 and E1, and the onset of E1 and F2, represent the net F1 and E1 amplitude, respectively (Fig. 3). The mean net F1 knee amplitude was 188 in telemark skiing, 528 in telemark jumps and 958 in barbell squats. The corresponding mean net E1 amplitudes were 128, 378 and 1098, respectively. The net knee amplitude during telemark jumps was larger than during telemark skiing, reflecting a larger knee extension angle at the onset of flexion and greater flexion in the knee joint at the onset of E1. The net F1 amplitude during telemark jumps and barbell squats was greater than in telemark skiing (P50.05), and the net E1 amplitude during

Results The knee angular displacement data showed that both telemark skiing and dry-land telemark jumps had four distinct phases. These phases were accompanied by EMG activity bursts of the vastus lateralis when the mechanical load was applied to the leg during the thrust phase (F1 and E1) (see Figs. 1A,B). Figure 1 also shows a small and less regular EMG burst that occurred during flexion and extension when the leg was on the inside. This corresponds to parts of the F2 and E2 phases (cf. Fig. 2). It can be observed that the highest pressure under the foot in telemark skiing and the only pressure increase during telemark jumps occurred in the F1 and E1 phases of the knee joint. During barbell squats (Fig. 1C), a movement cycle was constituted by the E1 and F1 phases, with EMG activity in the vastus lateralis occurring during both phases. Figure 2 shows the temporal pattern of knee angular displacement and the burst duration of the vastus

Fig. 3. Mean (+ s) net knee angular amplitude during telemark skiing and two different dry-land exercises. F = flexion phase and E = extension phase (for definition of F and E phases, see the Methods section). Difference between onset of F1 and onset of E1 corresponds to net F1 amplitude. Consequently, difference between onset of E1 and onset of F2 corresponds to net E1 amplitude. *Significant difference between dry-land exercise and telemark skiing (P50.05).

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barbell squats was greater than in telemark skiing (P50.05). Figure 4 shows the knee angular velocity during the loaded phase in telemark skiing and dry-land exercises. The lowest mean knee angular velocity occurred in telemark skiing, at approximately 0.47 rad × s71, followed by barbell squats at approximately 1.22 rad × s71. The angular velocity during telemark jumps was 2.34 and 1.59 rad × s71 in F1 and E1, respectively. The knee angular velocity during telemark jumps and barbell squats was significantly greater than during telemark skiing (P50.05). The cycle duration was significantly longer (P50.05) for telemark skiing (2.93 s) than telemark jumps (2.15 s) (see Table 1). Telemark skiing showed a mean EMG activity in the vastus lateralis of about 75% normalized to the EMG in maximal countermovement jumps, which was similar to the dry-land exercises (Fig. 5). There was no significant difference between telemark skiing and the dry-land exercises in terms of mean EMG activity.

Discussion

Fig. 4. Mean (+ s) knee angular velocity of the F1 and E1 phases during telemark skiing and two different dry-land exercises. F = flexion phase and E = extension phase (for definition of F and E phases, see the Methods section). *Significant difference between dry-land exercise and telemark skiing (P50.05).

Fig. 5. Mean (+s) normalized vastus lateralis EMG amplitude in telemark skiing and two different dry-land exercises. The EMG is normalized to mean amplitude during three maximal countermovement jumps. *Significant difference between dry-land exercise and telemark skiing (P50.05).

Mean EMG amplitude (%)

The results presented here for telemark skiing are similar to those reported previously for the giant slalom (Berg et al., 1995; Hintermeister et al., 1995) for knee extensor activation periods in the skiing cycle. The largest extensor activity occurred during the steering phase when the skiers were turning on the outside ski (corresponding to the F1 and E1 phases of the knee angular displacement cycle in the present study) (Figs. 1A and 2A). An eccentric–concentric muscle action was emphasized by Berg et al. (1995), and this was also seen in the present study. The knee angular amplitudes in the different phases of the telemark skiing cycle were similar to those obtained in the giant slalom (Berg et al., 1995). We found a slow angular velocity during the F1 and E1 phases of approximately 0.42 rad × s71. This was in the range of the angular displacement reported for the giant slalom by Berg et al. (1995), where it varied between 0.35 and

Table 1. Phase and cycle duration in telemark skiing, dry-land telemark jumps and barbell squats (mean+s) Phase duration

Telemark skiing Telemark jumps Barbell squats

F1

E1

F2

E2

Cycle duration

0.77+0.25 0.41+0.11 1.49+0.33

0.47+0.26 0.43+0.12 1.54+0.28

1.10+0.12 0.39+0.08 —

0.68+0.07 0.92+0.29 —

2.93+0.09 2.15+0.40 3.03+0.56

Note: F = flexion phase and E = extension phase (for definition of F and E phases, see the Methods section). Cycle and phase durations are in seconds.

EMG and kinematics of telemark skiing and dry-land exercise 0.7 rad × s71. The mean muscle activation amplitude during telemark skiing was approximately 75% of peak EMG obtained during maximal countermovement jumps in this study, but has been reported to be 58% in the giant slalom (Berg et al., 1995) and to vary between 58 and 112% (Hintermeister et al., 1995) when normalized to isometric maximal voluntary contractions. It is clear from our results and the studies referred to above on knee angular displacement and EMG that the knee extensor musculature seems to play an integral and important role in the generation of the ski turn in the giant slalom as well as in telemark skiing. The aim of the present study was to evaluate strength training exercises for telemark skiing with respect to specificity in knee angular amplitude, angular velocity, muscle action and level of activation. We focused on the F1 and E1 phases during which the external mechanical load is relatively large. Both telemark jumps and barbell squats showed a similar eccentric–concentric muscle activation pattern to telemark skiing. There was a difference in net F1 and E1 amplitudes between telemark skiing and the dry-land strength training exercises, the range in amplitude being greater for the training exercises. Therefore, the neuromotor system may be adapted to a larger range than during telemark skiing. A larger range will result in an adaptation inside the actual amplitude range, but there is no guarantee that the specific activation of the musculature is the same. Nevertheless, it is reasonable to assume that a larger range is better than a smaller one. The fine-tuning of knee angular amplitude at the onset and offset of the different phases is still absent. However, using this knowledge it is possible to adjust the onset of F1, E1 and F2 to resemble that of telemark skiing more closely in both telemark jumps and barbell squats. Knee angular velocity, which relates to the velocity of muscle action, was higher in the training exercises than in telemark skiing. The closest mean angular velocities to telemark skiing were seen in barbell squats, where they were higher. Telemark jumps showed a much higher angular velocity in F1 and E1, respectively. The angular velocity in barbell squats and, to some extent, telemark jumps may be adjusted to better simulate the knee angular velocity in telemark skiing. The difficulty in adjusting knee angular velocity in telemark jumps at impact is possibly related to the large amount of friction between the sole of the shoe and the ground. The normalized EMG activity in telemark skiing and in the strength exercises was approximately 75% of that during maximal countermovement jumps. Hence, the training exercises at least reached the mean EMG activity of telemark skiing. McDonagh and Davies

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(1984) showed that approximately 70% of maximum tension in 1-RM is sufficient for a strength gain. A relative activation of 70% of EMG activation during maximal countermovement jumps or more should enable a large part of the motor unit population to be recruited; this is presumably in the vicinity of the relative activation and tension that allow a strength gain. The similarity in activation between the barbell squats (at 1- to 3-RM), which is assumed to provide a strength gain (McDonagh and Davies, 1984), and telemark skiing, as well as telemark jumps, supports this assumption. This also supports the assumption that telemark skiing, per se, can stimulate an increase in strength. We conclude that the strength training exercises examined showed similar muscle action and EMG activity in the vastus lateralis during F1 and E1 as in telemark skiing. The activities recorded in telemark skiing, telemark jumps and barbell squats were all high enough to stimulate a strength gain. Dry-land exercises showed a larger extension and flexion amplitude and angular velocity than telemark skiing. It is believed that an adjustment in angular velocity in barbell squats and an adjustment in knee angle amplitude in both telemark jumps and barbell squats will lead to improved specificity.

Acknowledgements This study was supported by grants from the Norwegian University of Sport and Physical Education, Oslo, and University College of Physical Education and Sports, Stockholm, which are gratefully acknowledged.

References Berg, H.E., Eiken, O. and Tesch, P.A. (1995). Involvement of eccentric muscle actions in giant slalom racing. Medicine and Science in Sports and Exercise, 27, 1666–1670. Caiozzo, J., Perrine, T. and Edgerton, V.R. (1981). Training induced alterations in the in-vivo force–velocity relationship of human muscle. Journal of Applied Physiology, 51, 750–754. Hintermeister, R.A., O’Connor, D.D., Dillman, C.J. et al. (1995). Muscle activity in slalom and giant slalom skiing. Medicine and Science in Sports and Exercise, 27, 315–322. Kanehisa, H. and Miyashita, M. (1983). Specificity of velocity in strength training. European Journal of Applied Physiology, 52, 104–106. Komi, P.V. (1986). Training of muscle strength and power: interaction of neuromotoric, hypertrophic, and mechanical factors. International Journal of Sports Medicine, 7, 10–15. Lesmes, G. (1978). Muscle strength and power changes during maximal isokinetic training. Medicine and Science in Sports and Exercise, 10, 266–269.

364 Lindinger, S., Mu¨ller, E., Niessen, W., Schwameder, H. and Ko¨sters, A. (2001). Comparative biomechanical analysis of modern skating techniques and special skating simulation drills on world-class level. In Science and Skiing II (edited by E. Mu¨ller, H. Schwameder, C. Raschner, S. Lidinger and E. Kornexl), pp. 262–285. Hamburg: Verlag Dr. Kovac. McDonagh, M.J.N. and Davies, C.T.M. (1984). Adaptive responses of mammalian skeletal muscle to exercise with high loads. European Journal of Applied Physiology, 52, 139– 155. Mu¨ller, E. (1994). Analysis of the biomechanical characteristics of different swinging techniques in alpine skiing. Journal of Sports Sciences, 12, 261–278. Raschner, C., Mu¨ller, E. and Schwameder, H. (1997). Kinematic and kinetic analysis of slalom turns as a basis for the development of specific training methods to improve strength and endurance. In Science and Skiing I (edited by E. Mu¨ller, H. Schwameder, E. Kornexl and C. Raschner), pp. 251–271. London: E & FN Spon. Sale, D.G. (1988). Neural adaptation to resistance training. Medicine and Science in Sports and Exercise, 20, S135–S145.

Nilsson and Haugen Sale, D.G. and MacDougall, D. (1981). Specificity in strength training: a review for the coach and athlete. Canadian Journal of Applied Sports Sciences, 6, 87–92. Schwameder, H., Mu¨ller, E., Raschner, C. and Brunner, F. (1997). Aspects of technique-specific strength training in ski-jumping. In Science and Skiing I (edited by E. Mu¨ller, H. Schwameder, E. Kornexl and C. Raschner), pp. 309– 319. London: E & FN Spon. Seger, J. and Thortensson, A. (1994). Muscle strength and myoelectric activity in prepubertal and adult males and females. European Journal of Applied Physiology, 69, 81–87. Tesch, P.A., Dudley, G.A., Duvoisin, M.R. and Hather, B.M. (1990). Force and EMG signal patterns during repeated bouts of concentric and eccentric muscle actions. Acta Physiologica Scandinavica, 138, 263–271. Thepaut-Mathieu, C., Van Hoecke, J. and Maton, B. (1988). Myoelectrical and mechanical changes linked to length specificity during isometric training. Journal of Applied Physiology, 64, 1500–1505.