Biomedical subjects

P V Komi

Publications and source records attributed to P V Komi.

At least 19 recordsLinked to original sources

PubMed2006

Intensity- and muscle-specific fascicle behavior during human drop jumps.

The present study was designed to examine fascicle-tendon interaction in the synergistic medial gastrocnemius (MG) and soleus (Sol) muscles during drop jumps (DJ) performed from different drop heights (DH). Eight subjects performed unilateral DJ with maximal rebounds on a sledge apparatus from different DH. During the exercises, fascicle lengths (using ultrasonography) and electromyographic activities were recorded. The results showed that the fascicles of the MG and Sol muscles behaved differently during the contact phase, but the whole muscle-tendon unit and its tendinous tissue lengthened before shortening in both muscles. The Sol fascicles also lengthened before shortening during the ground contact in all conditions. During the braking phase, the Sol activation increased with increasing DH. However, the amplitude of Sol fascicle lengthening was not dependent on DH during the same phase. In the MG muscle, the fascicles primarily shortened during the braking phase in the lower DH condition. However, in the higher DH conditions, the MG fascicles either behaved isometrically or were lengthened during the braking phase. These results suggest that the fascicles of synergistic muscles (MG and Sol) can behave differently during DJ and that, with increasing DH, there may be specific length change patterns of the fascicles of MG but not of Sol.

Adult↗

PubMed2006

Medial gastrocnemius muscle behavior during human running and walking.

Utilization of elastic energy in the tendinous tissues (TT) of the human skeletal muscle may be task dependent. The present study was designed to investigate this problem by comparing the fascicle-TT interaction of the medial gastrocnemius muscle (MG) during ground contact of running and walking. Seven subjects ran and walked with a natural cadence. Ankle and knee joint angular data were recorded by electrogoniometers for estimating the entire MG muscle-tendon unit (MTU) length, together with the ground reaction forces. The MG fascicle length was measured by using the high-speed ultrasound image scanning during movements. The results showed that in running, after the rapid early fascicle stretching (0-10% of the contact period), the fascicles shortened throughout the ground contact while TT was stretched prior to shortening. In walking, the fascicles shortened initially (0-15% of the contact period) due to sudden plantar-flexion. Thereafter, the fascicles and TT lengthened slowly until the end of single support (15-70% of the contact period.). The fascicles then shorted during the push-off phase (70-100% of the contact period). These results demonstrate that the MG fascicles behaved differently between running and walking and did not follow the length change pattern of the MTU during the ground contact period. The estimated working range of active muscle fibers in force-length relationship could shift more to an ascending limb (shorter length) phase in running than in walking. These results suggest that MG fascicles can work within the optimal working range of the sarcomeres in the force-length relation but are responsible for the effective utilization of the TT elasticity during human running.

Adult↗

PubMed2006

Changes in the soleus muscle architecture after exhausting stretch-shortening cycle exercise in humans.

This study focused on the architectural changes in the muscle-tendon complex during the immediate and secondary (delayed) reductions of performance (bimodal recovery) caused by an exhaustive rebound type stretch-shortening cycle (SSC) exercise. The isometric plantar flexor torque during maximum voluntary contraction (MVC) was measured together with recording of electromyography (EMG) and ultrasonography from the soleus muscle before (BEF), after (AFT), 2 h (2H), 2 and 8 days (2D, 8D) after the SSC exercise (n=8). The performance variables (MVC torque and EMG activation) followed the bimodal recovery patterns. This was not the case in the changes of the fascicle length and muscle thickness. The relative torque changes in MVC correlated positively (R=0.78, P=0.02) to the corresponding averaged EMG changes between BEF and 2H (BEF-->2H); the significance disappeared in the comparison between 2H and 2D (2H-->2D), during which period MVC showed a secondary reduction. The relative torque changes in MVC showed no correlation with the changes in muscle thickness between BEF-2H. However, this correlation between 2H-2D was negative (R=-0.85, P<0.01). The fascicle shortening/average EMG ratio in MVC increased at 2H, and then decreased more at 2D than 2H (P<0.05). Thus, the secondary performance decline was not related to the corresponding EMG reduction but to the increased muscle thickness, which peaked at 2D. The results suggest clearly that the secondary decline in MVC could be related to the increase in muscle volume.

Adult↗

PubMed2006

Maximal force during eccentric and isometric actions at different elbow angles.

The purpose of this study was to examine a course of force potentiation and/or inhibition during maximal voluntary eccentric action. Maximal voluntary force (MVC) of elbow flexion of ten healthy male volunteers was measured during isometric and isokinetic eccentric action starting from 80 degrees or 110 degrees and ending at 140 degrees elbow angle. Surface EMG was recorded from biceps brachii (BB) and brachioradialis (BR) muscles. Maximal voluntary eccentric force during the first 10 degrees of the movement was higher (P<0.001) than the maximal voluntary isometric preactivation force both in 80 degrees and in 110 degrees starting position at all three velocities (1, 2, and 4 rad s(-1)). The relative force potentiation was velocity dependent being smallest at the lowest stretching speed (P<0.01). Average EMG (aEMG) of BB and BR decreased as the joint angle increased both in eccentric and in isometric actions but the decrease in aEMG towards extension was somewhat higher in eccentric actions as compared to isometric. It was concluded that the force measured during the first 10 degrees of eccentric contraction always exceeded the maximal voluntary isometric preactivation force regardless of the joint angle or of the movement velocity. When maximal voluntary preactivation preceded the stretch, the relative force potentiation seemed to be greater at higher stretching velocities (velocity dependent) while at lower preactivation levels, the velocity dependence was not observed. Decreased muscle activation and lower maximal voluntary force towards the end of the movement suggested inhibition during maximal voluntary eccentric actions.

Adult↗

PubMed2006

Effects of exhaustive stretch-shortening cycle exercise on muscle blood flow during exercise.

AIM: The influence of exhaustive stretch-shortening cycle exercise (SSC) on skeletal muscle blood flow (BF) during exercise is currently unknown. METHODS: Quadriceps femoris (QF) BF was measured in eight healthy men using positron emission tomography before and 3 days after exhaustive SSC exercise. The SSC protocol consisted of maximal and submaximal drop jumps with one leg. Needle biopsies of the vastus lateralis muscles were taken immediately and 2 days after SSC for muscle endothelial nitric oxide synthase (eNOS) and interleukin-1-beta (IL-1beta) mRNA level determinations. RESULTS: All subjects reported subjective muscle soreness after SSC (P < 0.001), which was well in line with a decrease in maximal isometric contraction force (MVC) and increase in serum creatine kinase activity (CK) (P = 0.018). After SSC muscle BF was 25% higher in entire QF (P = 0.043) and in its deep and superficial muscle regions, whereas oxygen uptake remained unchanged (P = 0.893). Muscle biopsies revealed increased IL-1beta (30 min: 152 +/- 75%, P = 0.012 and 2 days: 108 +/- 203%, P = 0.036) but decreased or unchanged eNOS (30 min; -21 +/- 57%, P = 0.050 and 2 days: +101 +/- 204%, P = 0.779) mRNA levels after SSC. CONCLUSION: It was concluded that fatiguing SSC exercise induces increased muscle BF during exercise, which is likely to be associated with pro-inflammatory processes in the exercised muscle.

Adult↗

PubMed2005

Interaction between fascicle and tendinous tissues in short-contact stretch-shortening cycle exercise with varying eccentric intensities.

The interaction between fascicle and tendinous tissues (TT) in short-contact drop jumps (DJ) with three different drop heights [low (Low), optimal (OP), and high (High)] was examined with 11 subjects. The ground reaction force (F(z)) and ankle and knee joint angles were measured together with real-time ultrasonography (fascicle length) and electromyographic activities of the medial gastrocnemius (MG) and vastus lateralis (VL) muscles during the movement. With increasing drop height, the braking force and flight time increased from Low to OP (P < 0.05). In High, the braking force increased but the flight time decreased compared with OP (P < 0.05). During contact of Low and OP conditions, the length of muscle-tendon unit and TT underwent lengthening before shortening in both MG and VL muscles. However, the two muscles differed in the fascicle behaviors. The MG fascicles behaved isometrically or shortened, and the VL fascicles underwent lengthening before shortening during contact. In High, the TT lengthening in both muscles decreased compared with OP (P < 0.05). The rapid stretch occurred in the MG fascicles but not in VL fascicles during the braking phase. The elastic recoil ratio decreased in both muscles with increasing the intensity during DJ. These findings demonstrated that TT underwent lengthening before shortening during DJ. However, the efficacy of elastic recoil decreased with increasing the drop intensity. The effective catapult action in TT can be limited by the drop intensity. In addition, the measured muscles behaved differently during DJ, providing evidence that each muscle may have a specific means of fascicle-TT interaction.

Adult↗

PubMed2005

Effects of effort and EMG levels on short-latency stretch reflex modulation after varying background muscle contractions.

It is known that the short-latency stretch reflex (SLSR) is modulated by the background muscle activity when it is elicited at matched torque levels. This study was designed to examine the effects of muscle contraction types before a stretch perturbation on SLSR in the human soleus muscle (SOL) when SLSR was elicited at the same levels of effort and at matched electromyographic (EMG) activity levels. A mechanical stretch perturbation was applied to the calf muscles when the ankle joint reached a ninety degree tibio-tarsal joint angle after the muscles performed an isometric (pre-ISO), shortening (pre-SHO) and lengthening contraction (pre-LEN). Subjects were seated on an ankle ergometer chair and developed 0%, 10%, 20%, 30%, 40%, 50%, 60% and 70% ankle joint torque (AJT) of maximum voluntary isometric plantar flexion contraction at 80 degrees in pre-SHO, at 90 degrees in pre-ISO and at 100 degrees in pre-LEN. After that, isometric or dynamic contractions started, and the subjects were asked to maintain effort levels as, needed, to maintain the target torque levels until the end of the stretch. They relaxed their muscles fully after the stretch. This chain of processes was consecutively repeated 10 times. EMG signals obtained from SOL were averaged after they were high-pass filtered and full-wave rectified. Some major findings resulted: (1) there were no differences in SLSR area in the active muscle between pre-ISO and pre-SHO, whereas its waveform was steeper in pre-ISO than in pre-SHO. (2) SLSR p-to-p amplitude and waveform were larger and steeper in the active muscle than in the relaxed one in all conditions, whereas they were independent of the effort levels once the muscle was activated. This led to steady SLSR modulation in response to the background muscle contraction in the active muscle regardless of whether the SLSR was elicited at matched AJT or EMG activity levels. These findings suggest that SLSR is closely related to the muscle spindle sensitivity influenced by the following factors: (1) the background muscle contraction type, and (2) gamma motoneuron activity set by CNS based on the effort level.

Adaptation, Physiological↗

PubMed2005

Effects of power training on muscle structure and neuromuscular performance.

The present study examines changes in muscle structure and neuromuscular performance induced by 15 weeks of power training with explosive muscle actions. Twenty-three subjects, including 10 controls, volunteered for the study. Muscle biopsies were obtained from the gastrocnemius muscle before and after the training period, while maximal voluntary isometric contractions (MVC) and drop jump tests were performed once every fifth week. No statistically significant improvements in MVC of the knee extensor (KE) and plantarflexor muscles were observed during the training period. However, the maximal rate of force development (RFD) of KE increased from 18,836+/-4282 to 25,443+/-8897 N (P<0.05) during the first 10 weeks of training. In addition, vertical jump height (vertical rise of the center of body mass) in the drop jump test increased significantly (P<0.01). Simultaneously, explosive force production of KE muscles measured as knee moment and power increased significantly; however, there was no significant change (P>0.05) in muscle activity (electromyography) of KE. The mean percentage for myosin heavy chain and titin isoforms, muscle fiber-type distributions and areas were unchanged. The enhanced performance in jumping as a result of power training can be explained, in part, by some modification in the joint control strategy and/or increased RFD capabilities of the KE.

Adult↗

PubMed2004

The effects of muscle history on short latency stretch reflex response of soleus muscle.

The purpose of the present study was to investigate the combined effects of muscle history, activation and stretching velocity on short latency stretch response (SLR). Stretches (70, 120 and 200 deg s-1) were elicited to both passive and active (10-25% MVC) triceps surae muscle with constant (ISO), lengthened (LEN) or shortened (SHO) muscle length. Under the passive SHO pre-condition both SLR amplitude and reflex torque (RT) decreased where as latency increased compared with the passive ISO pre-condition. Such observations were absent in active trials. Stretches applied to a lengthening passive muscle (LEN) resulted in smaller SLR amplitude and RT compared with passive ISO. In active muscle the stretch response increased with stretching velocity in ISO and SHO. However, in LEN there was large interindividual variability and no velocity dependent increase in SLR amplitude was observed. Smaller amplitude and longer latency of passive SLR in SHO could result from increased slack in the intrafusal fibres, which may be compensated by fusimotor activation during the active condition. The mechanism behind the smaller amplitude in passive LEN and the lack of velocity dependence in active LEN may be related to changes in motoneuron pool excitability or changes in the spindle sensitivity to stretch.

Adaptation, Physiological↗

PubMed2004

Gait asymmetry in patients with limb length discrepancy.

Foot loading patterns and neuromuscular function of both limbs during walking were investigated on 25 patients with limb length discrepancy. Plantar pressures and 2-D ground reaction forces were recorded simultaneously with electromyographic activities at two different walking speeds. Bilateral comparison indicated that moderate limb length discrepancies resulted in asymmetrical gait patterns. The duration of the stance phase was reduced in the short limb in both walking speeds. The vertical ground reaction force (F) in the push-off phase was greater in the long limb both at normal (1.33 (SO, 0.05 BW) vs. 1.29 (SD, 0.09 BW)) (P=0.0027) and fast walking speed (1.55 (SD, 0.11) vs. 1.48 (SD, 0.15 BW)) (P=0.001). Peak plantar pressures were higher under the big toe in the long leg and the heel-off occurred faster. The push-off phase was initiated earlier in the short leg. The maximum isometric torque of the long limb was considerably greater (673 Nm vs. 239 Nm) (P=0.026). The results imply that the loading of the long limb is greater and the foot loading patterns shifted more to the forefoot in the long, limb to compensate walking disturbances caused by limb length discrepancies.

Adolescent↗

PubMed2003

Voluntary activation and mechanical performance of human triceps surae muscle after exhaustive stretch-shortening cycle jumping exercise.

The purpose of this study was to examine neuromuscular factors that may contribute to post exercise force loss and subsequent recovery after exhaustive stretch-shortening cycle (SSC) exercise. Six subjects were fatigued on a sledge apparatus by 100 maximal rebound jumps followed by continuous submaximal jumping until complete exhaustion. Exercise-induced changes in neuromuscular performance were followed up to 7 days post exercise. The total number of jumps in the SSC exercise ranged from 336 to 1392. The SSC exercise induced a significant immediate plantarflexion torque decline of 29, 38 and 44% ( P<0.05) in maximal voluntary contraction and evoked maximal twitch and low-frequency (LF) stimulation, respectively. The higher the number of jumps in the SSC exercise the larger was the post exercise reduction in voluntary activation as well as in contractile force ( r=-0.94, P<0.01, in both). Furthermore, a higher number of jumps augmented a delayed force recovery and late decline in stretch reflex EMG response ( r=-0.94, P<0.01). Clear differences were found in central and peripheral adaptation to the exhaustive SSC exercise between the subjects. The magnitude of post exercise contractile and activation failure as well as the delayed recovery of neuromuscular performance may have been augmented in some subjects due to their high number of jumps in the exercise.

Adaptation, Physiological↗

PubMed2003

Effects of power training on mechanical efficiency in jumping.

The present study investigates the effects of power training on mechanical efficiency (ME) in jumping. Twenty-three subjects, including ten controls, volunteered for the study. The experimental group trained twice a week for 15 weeks performing various jumping exercises such as drop jumps, hurdle jumps, hopping and bouncing. In the maximal jumping test, the take-off velocity increased from 2.56 (0.24) m.s(-1) to 2.77 (0.18) m.s(-1) ( P<0.05). In the submaximal jumping of 50% of the maximum, energy expenditure decreased from 660 (110) to 502 (68) J.kg(-1).min(-1) ( P<0.001) while, simultaneously, ME increased from 37.2 (8.4)% to 47.4 (8.2)% ( P<0.001). Some muscle enzyme activities of the gastrocnemius muscle increased during the training period: citrate synthase from 35 (8) to 39 (7) micromol.g(-1) dry mass.min(-1) ( P<0.05) and beta-hydroxyacyl CoA dehydrogenase from 21 (4) to 23 (5) micromol.g(-1) dry mass.min(-1) ( P<0.05), whereas no significant changes were observed in phosphofructokinase and lactate dehydrogenase. In the control group, no changes in ME or in enzyme activities were observed. In conclusion, the enhanced performance capability of 8% in maximal jumping as a result of power training was characterized by decreased energy expenditure of 24%. Thus, the increased neuromuscular performance, joint control strategy, and intermuscular coordination (primary factors), together with improved aerobic capacity (secondary factor), may result in reduced oxygen demands and increased ME.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2003

Effects of long- and short-term fatiguing stretch-shortening cycle exercises on reflex EMG and force of the tendon-muscle complex.

This study examined the fatigue effects of stretch-shortening cycle exercises of different intensity and duration on stretch reflex EMG and mechanical responses of the triceps surae muscle. Twelve subjects performed either a 10-km run ( n=6) or short but exhaustive rebound exercise on a sledge apparatus ( n=6). Passive reflex tests (mechanically induced ankle dorsiflexions) were examined before, after as well as 2 h, 2 and 7 days after exercise. Mechanical reflex responses were recorded from the ergometer torque signal. An acute contractile failure was observed as large reductions in twitch responses, especially in the sledge subgroup who showed high post-exercise peak blood lactate and an increased EMG/torque ratio. Independently of the exercise, the delayed fatigue analysis revealed strong relationships between the reflex-induced EMG and mechanical changes. In addition to muscle damage, these results may be explained by inhibitory effects via the sensitisation of small muscle afferents particularly during the exercise-induced delayed recovery process.

Adolescent↗

PubMed2003

Leucine supplementation does not enhance acute strength or running performance but affects serum amino acid concentration.

This study described the effect of leucine supplementation on serum amino acid concentration during two different exercise sessions in competitive male power athletes. The subjects performed a strength exercise session (SES; n = 16; 26 +/- 4 years) or a maximal anaerobic running exercise session (MARE; n = 12; 27 +/- 5 years) until exhaustion twice at a 7-day interval. The randomized subjects consumed drinks containing leucine (100 mg x kg/body weight before and during SES or 200 mg x kg/body weight before MARE) or placebo. Blood specimens taken 10 min before (B) and after (A) the sessions were analyzed for serum amino acids. In SES the concentration of leucine was distinctly higher in the leucine supplemented group than in the placebo group in both B (p < 0.001) and A (p < 0.001) samples. The leucine concentration decreased in placebo but not in the leucine supplemented group following the exercise session. Isoleucine (p = 0.017) and valine (p = 0.006) concentration decreased more in the leucine supplemented group than in placebo in A samples. In MARE the concentration of leucine was higher in the leucine supplemented group than in placebo in both B (p < 0.001) and A (p < 0.001) samples and increased (p < 0.001) in the supplemented group following the session. Isoleucine (p = 0.020) and valine (p = 0.006) concentration decreased in the supplemented group in A samples. There were no differences in a counter movement jump after SES or in the running performance in MARE between the leucine supplemented group and placebo. These findings indicate that consuming leucine before or before and during exercise sessions results in changes in blood amino acid concentration. However, the supplementation does not affect an acute physical performance.

Adult↗

PubMed2003

Motor unit activation patterns during isometric, concentric and eccentric actions at different force levels.

Motor unit activation patterns were studied during four different force levels of concentric and eccentric actions. Eight male subjects performed concentric and eccentric forearm flexions with the movement range from 100 degrees to 60 degrees in concentric and from 100 degrees to 140 degrees elbow angle in eccentric actions. The movements were started either from zero preactivation or with isometric preactivation of the force levels of 20, 40, 60 and 80% MVC. The subjects were then instructed to maintain the corresponding relative force levels during the dynamic actions. Intramuscular and surface EMG was recorded from biceps brachii muscle. Altogether 28 motoneuron pools were analyzed using the intramuscular spike-amplitude frequency (ISAF) analysis technique of Moritani et al. The mean spike amplitude was lower and the mean spike frequency higher in the isometric preactivation phase than in the consequent concentric and eccentric actions. When the movements started with isometric preactivation the mean spike amplitude increased significantly (P<0.001) up to 80% in isometric and concentric actions but in eccentric actions the increase continued only up to 60% (P<0.01). The mean spike frequency in isometric preactivation and in concentric action with preactivation was lower only at the 20% force level (P<0.01) as compared to the other force levels while in eccentric action with preactivation the increase between the force levels was significant (P<0.01) up to 60%. When the movement was started without preactivation the mean spike amplitude at 20% and at 40% force level was higher (P<0.01) in eccentric action than in concentric actions. It was concluded that the recruitment threshold may be lower in dynamic as compared to isometric actions. The recruitment of fast motor units may continue to higher force levels in isometric and in concentric as in eccentric actions which, on the other hand, seems to achieve the higher forces by increasing the firing rate of the active units. At the lower force levels mean spike amplitude was higher in eccentric than in concentric actions which might indicate selective activation of fast motor units. This was, however, the case only when the movements were started without isometric preactivation.

Adult↗

PubMed2003

Comparison of force-velocity relationships of vastus lateralis muscle in isokinetic and in stretch-shortening cycle exercises.

AIM: This study investigated the force-velocity characteristics of the vastus lateralis (VL) muscle fascicle and muscle-tendon unit (MTU) in isolated lengthening and shortening actions, and during natural movement. METHODS: Four subjects performed maximal eccentric and concentric knee extensions (60, 120 and 180 degrees s-1). Unilateral counter movement jumps and drop jumps in the sledge apparatus served as natural movements. Vastus lateralis fascicle lengths were determined from ultrasonography. In vivo patellar tendon forces (PTF) were measured with an optic fibre technique. Patellar tendon force was derived to VL force according to the cross-sectional area of the muscle. Force in the direction of fascicle was calculated by dividing the VL force value by cosine of the fascicle angle. Force-velocity curves were constructed using angle specific values from isokinetic knee extensions (classical curve) and using instantaneous values from jumping exercises. RESULTS: In the fascicle level, we did not find an enhanced muscle force in the jumping performances as compared with the classical force-velocity curve. In the muscle-tendon level, the instantaneous force at high muscle-tendon shortening speeds exceeded that extrapolated according to Hill's equation. CONCLUSION: This difference between fascicle and muscle-tendon behaviour suggests that the neural input in fast stretch-shortening cycle exercises minimizes the length changes in muscle fascicle and enables storage and recoil of energy from elastic components that contributes to the enhanced mechanical output of the MTU during the push-off phase.

Adult↗

PubMed2003

Behaviour of vastus lateralis muscle-tendon during high intensity SSC exercises in vivo.

AIMS: The interaction between fascicle and tendinous tissue of human vastus lateralis muscle was investigated during varying intensity stretch-shortening cycle (SSC) jumps performed on a sledge apparatus. METHODS: Eight subjects performed single leg squat (SJ) and drop jumps (DJ) from a constant dropping height but to different rebound heights. The fascicle length of the vastus lateralis muscle (VL) was determined from real-time ultrasonography during the movement. Tendon length changes were calculated by subtracting the horizontal part of the fascicle length from the muscle-tendon unit (MTU) length. Simultaneously, kinematic, kinetic and electromyographic data were recorded from leg muscles. In addition, the in vivo patella tendon force was measured from one subject during the trials. RESULTS: In all DJs, where MTU was stretched prior to shortening, the fascicle and tendinous tissue of the VL also underwent a SSC. The fascicle lengths decreased and the recoil of tendinous tissue increased with increased rebound intensities (P<0.05). The force-velocity curves obtained from the MTU showed the expected force-velocity relationship for SSC activities, demonstrating performance enhancement. However, the increased MTU power during the shortening phase of the movement was due primarily to the enhancement of the tendon compartment. CONCLUSION: The results of this study show that, at higher rebound intensities, the fascicle is controlled during the braking phase in a distinct manner so that the effective recoil of the tendon is possible during the final push-off phase. In addition, the results suggest that the behaviour of fascicle length change depends on the muscle in question in addition to the movement intensity.

Adult↗

PubMed2003

Neuromuscular behaviour of the triceps surae muscle-tendon complex during running and jumping.

The present study examined the behaviour of the Achilles tendon (AT) - triceps surae (TS) muscle complex during running and long jump take-off. High AT forces were measured in the push-off phase in running even with very low EMG activity. In the long jump, high rate of stiffness development was a characteristic of the braking phase of the jump. The results suggest that high and well-coordinated activation patterns of the leg extensor muscles during the preactivation and eccentric phases together with high stretching velocities of muscle-tendon complex provide basis for appropriate tendomuscular stiffness. This together with high force at the end of the eccentric phase enables an effective push-off (concentric) phase.

Achilles Tendon↗