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Performance Area => Peer Reviewed Studies Discussion => Topic started by: adarqui on June 04, 2009, 06:21:29 pm
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All conclusions of studies will be listed in this original post (TABLE OF SUMMARIES) for quick reference.
Post anything related to tendon / muscle / joint stiffness & performance. This could be anything related to different training methods & their effect on stiffness, and the effect of this training on performance (sprinting/jumping etc).
1. Influence of elastic properties of tendon structures on jump performance in humans
Although the stiffness was not significantly related to absolute jump height in either vertical jump, it was inversely correlated with the difference in jump height between the vertical jumps performed with and without countermovement. The results suggested that the stiffness of tendon structures has a favorable effect on stretch-shortening cycle exercise, possibly due to adequate storage and recoil of elastic energy.
2. Effects of isometric squat training on the tendon stiffness and jump performance
These results suggest that isometric squat training changes the stiffness of human tendon aponeurosis complex in knee extensors to act negatively on the effects of pre-stretch during stretch-shortening cycle exercises.
3. Age-related neuromuscular function during drop jumps
These different activation patterns are in line with the mechanical behavior of GM (medial gastroc) showing significantly less fascicle shortening and relative TT (tendon tissue) stretching in the braking phase in the elderly than in the young subjects. These results suggest that age-specific muscle activation patterns as well as mechanical behaviors exist during DJs.
4. Influence of leg stiffness and its effect on myodynamic jumping performance.
The leg and ankle stiffness values were higher when the contact times were shorter. This means that by influencing contact time through verbal instructions it is possible to control leg stiffness.
5. Leg stiffness primarily depends on ankle stiffness during human hopping
Thus, we conclude that the primary mechanism for leg stiffness adjustment is the adjustment of ankle stiffness.
6. Muscle performance during maximal isometric and dynamic contractions is influenced by the stiffness of the tendinous structures
Power, force, and velocity parameters obtained during the jumps were significantly correlated to tendon stiffness. These data indicate that muscle output in high-force isometric and dynamic muscle actions is positively related to the stiffness of the tendinous structures, possibly by means of a more effective force transmission from the contractile elements to the bone.
7. Effect of landing stiffness on joint kinetics and energetics in the lower extremity.
Overall, the muscular system absorbed 19% more of the body's kinetic energy in the soft landing compared with the stiff landing, reducing the impact stress on other body tissues. The ankle plantarflexors provided the major energy absorption function in both conditions, averaging 44% of the total muscular work done followed by the knee (34%) and hip (22%) extensors.
8. Effects of Plyometric and Weight Training on Muscle-Tendon Complex and Jump Performance.
Conclusion: These results indicate that the jump performance gains after plyometric training are attributed to changes in the mechanical properties of muscle-tendon complex, rather than to the muscle activation strategies.
9. Relationships between three potentiation effects of plyometric training and performance
Conclusions: Plyometric training specifically potentiated the normalized EMG, tendon stiffness and elastic energy utilization in the myotendinous complex of the triceps surae. Although these changes are possibly essential determinants, only increases of tendon stiffness were observed to correlate with performance improvements.
10. Effects of different duration isometric contractions on tendon elasticity in human quadriceps muscles
Stiffness increased significantly for the long-duration protocol, but not for the short-duration protocol.
The present study demonstrates a greater increase in stiffness of human tendon structures following isometric training using longer duration contractions compared to shorter contractions. This suggests that the changes in the elasticity of the tendon structures after resistance training may be affected by the duration of muscle contraction.
11. Effects of isometric training on the elasticity of human tendon structures in vivo
Thus the present results indicate that isometric training increases the stiffness and Young's modulus of human tendon structures as well as muscle strength and size. This change in the tendon structures would be assumed to be an advantage for increasing the rate of torque development and shortening the electromechanical delay.
12. Effect of habitual running on human Achilles tendon load-deformation properties and cross-sectional area
The total running duration was ~43 h, distributed over 34 wk. Tendon-aponeurosis displacement during maximal voluntary contraction was unchanged. Tendon CSA also remained unchanged In conclusion, a total training stimulus of ~9 mo of running in previously untrained subjects was adequate to induce significant cardiovascular improvements, although it did not result in any changes in the mechanical properties of the triceps surea tendon-aponeurosis complex or in the dimensions of Achilles tendon.
13. Optimal muscle fascicle length and tendon stiffness for maximising gastrocnemius efficiency during human walking and running
Muscles generate force to resist gravitational and inertial forces and/or to undertake work, e.g. on the centre of mass. A trade-off in muscle architecture exists in muscles that do both; the fibres should be as short as possible to minimise activation cost but long enough to maintain an appropriate shortening velocity. Energetic cost is also influenced by tendon compliance which modulates the timecourse of muscle mechanical work. Here we use a Hill-type muscle model of the human medial gastrocnemius to determine the muscle fascicle length and Achilles tendon compliance that maximise efficiency during the stance phase of walking (1.2 m/s) and running (3.2 and 3.9 m/s). A broad range of muscle fascicle lengths (ranging from 45 to 70 mm) and tendon stiffness values (150–500 N/mm) can achieve close to optimal efficiency at each speed of locomotion; however, efficient walking requires shorter muscle fascicles and a more compliant tendon than running. The values that maximise efficiency are within the range measured in normal populations. A non-linear toe-region region of the tendon force–length properties may further influence the optimal values, requiring a stiffer tendon with slightly longer muscle fascicles; however, it does not alter the main results. We conclude that muscle fibre length and tendon compliance combinations may be tuned to maximise efficiency under a given gait condition. Efficiency is maximised when the required volume of muscle is minimised, which may also help reduce limb inertia and basal metabolic costs.
14. On muscle, tendon and high heels
We conclude that long-term use of high-heeled shoes induces shortening of the GM muscle fascicles and increases AT stiffness, reducing the ankle's active range of motion. Functionally, these two phenomena seem to counteract each other since no significant differences in static or dynamic torques were observed.
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Influence of elastic properties of tendon structures on jump performance in humans
Keitaro Kubo, Yasuo Kawakami, and Tetsuo Fukunaga
Department of Life Science (Sports Sciences), University of Tokyo, Tokyo 153, Japan
The purpose of this study was to quantify the elastic properties of tendon structures in vivo and to investigate the influence of the tendon properties on jump performance with and without countermovement. Elongation of the tendon and aponeurosis of vastus lateralis muscle (dL) was directly measured by ultrasonography while subjects (n = 31) performed ramp isometric knee extension up to the voluntary maximum (MVC). The relationship between muscle force and dL was fitted to a linear regression above 50% MVC, the slope of which was defined as stiffness of the tendon structures. Statistical analysis revealed no significant difference between duplicated measurements of stiffness, with an interday reliability of r = 0.88 and a coefficient of variance of 6.1%. Although the stiffness was not significantly related to absolute jump height in either vertical jump, it was inversely correlated with the difference in jump height between the vertical jumps performed with and without countermovement. The results suggested that the stiffness of tendon structures has a favorable effect on stretch-shortening cycle exercise, possibly due to adequate storage and recoil of elastic energy.
Effects of isometric squat training on the tendon stiffness and jump performance
Journal European Journal of Applied Physiology
Publisher Springer Berlin / Heidelberg
ISSN 1439-6319 (Print) 1439-6327 (Online)
Issue Volume 96, Number 3 / February, 2006
Accepted: 13 October 2005 Published online: 22 November 2005
Abstract The present study aimed to investigate the effect of isometric squat training on human tendon stiffness and jump performances. Eight subjects completed 12 weeks (4 days/week) of isometric squat training, which consisted of bilateral leg extension at 70% of maximum voluntary contraction (MVC) for 15 s per set (10 sets/day). Before and after training, the elongations of the tendon aponeurosis complex in the vastus lateralis muscle and patella tendon were directly measured using ultrasonography while the subjects performed ramp isometric knee extension up to MVC. The relationship between the estimated muscle force and tendon elongation was fitted to a linear regression, the slope of which was defined as stiffness. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The training significantly increased the volume (P<0.01) and MVC torque (P<0.01) of the quadriceps femoris muscle. The stiffness of the tendon aponeurosis complex increased significantly from 5122 (mean ± SD) to 59±24 N/mm (P=0.04), although that of the patella tendon did not change (P=0.48). The J height increased significantly after training (P=0.03), although the CMJ height did not (P=0.45). In addition, the relative difference in jump height between SJ and CMJ decreased significantly after training (P=0.02). These results suggest that isometric squat training changes the stiffness of human tendon aponeurosis complex in knee extensors to act negatively on the effects of pre-stretch during stretch-shortening cycle exercises.
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Age-related neuromuscular function during drop jumps
Muscle- and movement-specific fascicle-tendon interaction affects the performance of the neuromuscular system. This interaction is unknown among elderly and consequently contributes to the lack of understanding the age-related problems on neuromuscular control. The present experiment studied the age specificity of fascicle-tendon interaction of the gastrocnemius medialis (GM) muscle in drop jump (DJ) exercises. Twelve young and thirteen elderly subjects performed maximal squat jumps and DJs with maximal rebound effort on a sledge apparatus. Ankle and knee joint angles, reaction force, and electromyography (EMG) from the soleus (Sol), GM, and tibialis anterior (TA) muscles were measured together with the GM fascicle length by ultrasonography. The results showed that the measured ankle joint stiffness (AJS) during the braking phase correlated positively with the rebound speed in both age groups and that both parameters were significantly lower in the elderly than in young subjects. In both groups, the AJS correlated positively with averaged EMG (aEMG) in Sol during the braking phase and was further associated with GM activation (r = 0.55, P < 0.01) and TA coactivation (TA/GM r = –0.4 P < 0.05) in the elderly subjects. In addition, compared with the young subjects, the elderly subjects showed significantly lower GM aEMG in the braking phase and higher aEMG in the push-off phase, indicating less utilization of tendinous tissue (TT) elasticity. These different activation patterns are in line with the mechanical behavior of GM showing significantly less fascicle shortening and relative TT stretching in the braking phase in the elderly than in the young subjects. These results suggest that age-specific muscle activation patterns as well as mechanical behaviors exist during DJs.
Influence of leg stiffness and its effect on myodynamic jumping performance.
The purposes of this study are: a) to examine the possibility of influencing the leg stiffness through instructions given to the subjects and b) to determine the effect of the leg stiffness on the mechanical power and take-off velocity during the drop jumps. A total of 15 athletes performed a series of drop jumps from heights of 20, 40 and 60 cm. The instructions given to the subjects were a) "jump as high as you can" and b) "jump high a little faster than your previous jump". The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes body positions were recorded using a high speed (250 Hz) video camera. EMG was used to measure muscle activity in five leg muscles. The data was divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and group 5 the shortest. The leg and ankle stiffness values were higher when the contact times were shorter. This means that by influencing contact time through verbal instructions it is possible to control leg stiffness. Maximum center of mass take-off velocity the can be achieved with different levels of leg stiffness. The mechanical power acting on the human body during the positive phase of the drop jumps had the highest values in group 3. This means that there is an optimum stiffness value for the lower extremities to maximize mechanical power.
Leg stiffness primarily depends on ankle stiffness during human hopping
When humans hop in place or run forward, they adjust leg stiffness to accommodate changes in stride frequency or surface stiffness. The goal of the present study was to determine the mechanisms by which humans adjust leg stiffness during hopping in place. Five subjects hopped in place at 2.2Hz while we collected force platform and kinematic data. Each subject completed trials in which they hopped to whatever height they chose (“preferred height hopping”) and trials in which they hopped as high as possible (“maximum height hopping”). Leg stiffness was approximately twice as great for maximum height hopping as for preferred height hopping. Ankle torsional stiffness was 1.9-times greater while knee torsional stiffness was 1.7-times greater in maximum height hopping than in preferred height hopping. We used a computer simulation to examine the sensitivity of leg stiffness to the observed changes in ankle and knee stiffness. Our model consisted of four segments (foot, shank, thigh, head–arms–trunk) interconnected by three torsional springs (ankle, knee, hip). In the model, increasing ankle stiffness by 1.9-fold, as observed in the subjects, caused leg stiffness to increase by 2.0-fold. Increasing knee stiffness by 1.7-fold had virtually no effect on leg stiffness. Thus, we conclude that the primary mechanism for leg stiffness adjustment is the adjustment of ankle stiffness.
Muscle performance during maximal isometric and dynamic contractions is influenced by the stiffness of the tendinous structures
Submitted 19 November 2004 ; accepted in final form 19 April 2005
Contractile force is transmitted to the skeleton through tendons and aponeuroses, and, although it is appreciated that the mechanocharacteristics of these tissues play an important role for movement performance with respect to energy storage, the association between tendon mechanical properties and the contractile muscle output during high-force movement tasks remains elusive. The purpose of the study was to investigate the relation between the mechanical properties of the connective tissue and muscle performance in maximal isometric and dynamic muscle actions. Sixteen trained men participated in the study. The mechanical properties of the vastus lateralis tendon-aponeurosis complex were assessed by ultrasonography. Maximal isometric knee extensor force and rate of torque development (RTD) were determined. Dynamic performance was assessed by maximal squat jumps and countermovement jumps on a force plate. From the vertical ground reaction force, maximal jump height, jump power, and force-/velocity-related determinants of jump performance were obtained. RTD was positively related to the stiffness of the tendinous structures (r = 0.55, P < 0.05), indicating that tendon mechanical properties may account for up to 30% of the variance in RTD. A correlation was observed between stiffness and maximal jump height in squat jumps and countermovement jumps (r = 0.64, P < 0.05 and r = 0.55, P < 0.05). Power, force, and velocity parameters obtained during the jumps were significantly correlated to tendon stiffness. These data indicate that muscle output in high-force isometric and dynamic muscle actions is positively related to the stiffness of the tendinous structures, possibly by means of a more effective force transmission from the contractile elements to the bone.
Effect of landing stiffness on joint kinetics and energetics in the lower extremity.
CASE STUDY
Medicine & Science in Sports & Exercise. 24(1):108-115, January 1992.
DEVITA, PAUL; SKELLY, WILLIAM A.
Abstract:
DEVITA, P. and W. A. SKELLY. Effect of landing stiffness on joint kinetics and energetics in the lower extremity. Med. Sci. Sports Exerc., Vol. 24, No. 1, pp. 108-115, 1992. Ground reaction forces (GRF), joint positions, joint moments, and muscle powers in the lower extremity were compared between soft and stiff landings from a vertical tall of 59 cm. Soft and still' landings had less than and greater than 90 degrees of knee flexion after floor contact. Ten trials of sagittal plane film and GRF data, sampled at 100 and 1000 Hz, were obtained from each of eight female athletes and two landing conditions. Inverse dynamics were performed on these data to obtain the moments and powers during descent (free fall) and floor contact phases. Angular impulse and work values were calculated from these curves, and the conditions were compared with a correlated t-test. Soft and stiff landings averaged 117 and 77 degrees of knee flexion. Larger hip extensor (0.010 vs 0.019 N [middle dot] m [middle dot] s [middle dot] kg-1; P < 0.01) and knee flexor (-0.010 vs -0.013 N [middle dot] m [middle dot] s [middle dot] kg-1; P < 0.01) moments were observed during descent in the stiff landing, which produced a more erect body posture and a flexed knee position at impact. The shapes of the GRF, moment, and power curves were identical between landings. The stiff landing had larger GRFs, but only the ankle plantarflexors produced a larger moment (0.185 vs 0.232 N [middle dot] m [middle dot] s [middle dot] kg-1; P < 0.01) in this condition. The hip and knee muscles absorbed more energy in the soft landing (hip, -0.60 vs -0.39 W [middle dot] kg-1; P < 0.01; knee, -0.89 vs -0.61 W [middle dot] kg-1; P < 0.01), while the ankle muscles absorbed more in the stiff landing (-0.88 vs -1.00 W [middle dot] kg-1; P < 0.05). Overall, the muscular system absorbed 19% more of the body's kinetic energy in the soft landing compared with the stiff landing, reducing the impact stress on other body tissues. The ankle plantarflexors provided the major energy absorption function in both conditions, averaging 44% of the total muscular work done followed by the knee (34%) and hip (22%) extensors.
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Effects of Plyometric and Weight Training on Muscle-Tendon Complex and Jump Performance.
APPLIED SCIENCES
Medicine & Science in Sports & Exercise. 39(10):1801-1810, October 2007.
KUBO, KEITARO 1; MORIMOTO, MASANORI 2; KOMURO, TERUAKI 2; YATA, HIDEAKI 3; TSUNODA, NAOYA 2; KANEHISA, HIROAKI 1; FUKUNAGA, TETSUO 4
Abstract:
Purpose: The purpose of this study was to investigate the effects of plyometric and weight training protocols on the mechanical properties of muscle-tendon complex and muscle activities and performances during jumping.
Methods: Ten subjects completed 12 wk (4 d[middle dot]wk-1) of a unilateral training program for plantar flexors. They performed plyometric training on one side (PT; hopping and drop jump using 40% of 1RM) and weight training on the other side (WT; 80% of 1RM). Tendon stiffness was measured using ultrasonography during isometric plantar flexion. Three kinds of unilateral jump heights using only ankle joint (squat jump: SJ; countermovement jump: CMJ; drop jump: DJ) on sledge apparatus were measured. During jumping, electromyographic activities were recorded from plantar flexors and tibial anterior muscle. Joint stiffness was calculated as the change in joint torque divided by the change in ankle angle during eccentric phase of DJ.
Results: Tendon stiffness increased significantly for WT, but not for PT. Conversely, joint stiffness increased significantly for PT, but not for WT. Whereas PT increased significantly jump heights of SJ, CMJ, and DJ, WT increased SJ only. The relative increases in jump heights were significantly greater for PT than for WT. However, there were no significant differences between PT and WT in the changes in the electromyographic activities of measured muscles during jumping.
Conclusion: These results indicate that the jump performance gains after plyometric training are attributed to changes in the mechanical properties of muscle-tendon complex, rather than to the muscle activation strategies.
Relationships between three potentiation effects of plyometric training and performance
This study measured the potentiation effects of plyometric training [normalized electromyography (EMG) in triceps surae, stiffness and elastic energy utilization of the Achilles tendon] and investigated the correlations between these effects and performances [voluntary electromechanical delay (EMD) and jump height]. Twenty-one subjects were randomly assigned either to the control group (10 subjects: age 22.3±1.6 years) or to a training group (11 subjects: age 22.1±1.6 years) that performed 8 weeks of plyometric training. Results: As compared with the performances before training, normalized EMG in the soleus were significantly (P?0.001) increased after 4 and 8 weeks of training. Tendon stiffness, elastic energy storage, release and jump height determined after training were significantly increased (P<0.05), with a concomitantly reduced voluntary EMD (P=0.01). These variables also showed significant differences vs the control group (all P<0.05). The other variables remained unchanged. Correlations were observed between tendon stiffness and either voluntary EMD (r=?0. 77, P=0.014) or jump height (r=0.54, P=0.031). Conclusions: Plyometric training specifically potentiated the normalized EMG, tendon stiffness and elastic energy utilization in the myotendinous complex of the triceps surae. Although these changes are possibly essential determinants, only increases of tendon stiffness were observed to correlate with performance improvements.
Effects of different duration isometric contractions on tendon elasticity in human quadriceps muscles
1.
The present study aimed to investigate the influence of isometric training protocols with long- and short-duration contractions on the elasticity of human tendon structures in vivo. The elasticity was assessed through in vivo determination of the elongation (L) of the tendons and aponeuroses using ultrasonography, while the subjects performed ramp isometric exercise up to maximum voluntary contraction (MVC).
2.
Eight young males completed 12 weeks (4 days per week) of a unilateral isometric training programme on knee extensors, which consisted of two different combinations of contraction and relaxation times at 70 % MVC: one leg was trained using a short-duration protocol (3 sets of 50 repetitions of contraction for 1 s and relaxation for 2 s), and the other leg was trained using a long-duration protocol (4 sets of a combination of contraction for 20 s and relaxation for 1 min). The training volume per session, expressed as the integrated torque, was the same for the two protocols.
3.
Both protocols resulted in a significant increase in MVC: 31.8 ± 17.2 % for the short-duration protocol and 33.9 ± 14.4 % for the long-duration protocol. Moreover, the training produced significant increases in the muscle volume of the constituents of the quadriceps femoris, with similar relative gains for the two protocols: 7.4 ± 3.9 % for the short-duration protocol and 7.6 ± 4.3 % for the long-duration protocol.
4.
The short-duration protocol produced no significant change in L values at any of the force production levels. For the long-duration protocol, however, the L values above 550 N were significantly shorter after training. Analysis revealed that the group × test time interaction effect on tendon stiffness was significant. Stiffness increased significantly for the long-duration protocol, but not for the short-duration protocol.
5.
The present study demonstrates a greater increase in stiffness of human tendon structures following isometric training using longer duration contractions compared to shorter contractions. This suggests that the changes in the elasticity of the tendon structures after resistance training may be affected by the duration of muscle contraction.
Effects of isometric training on the elasticity of human tendon structures in vivo
The present study aimed to investigate the effect of isometric training on the elasticity of human tendon structures. Eight subjects completed 12 wk (4 days/wk) of isometric training that consisted of unilateral knee extension at 70% of maximal voluntary contraction (MVC) for 20 s per set (4 sets/day). Before and after training, the elongation of the tendon structures in the vastus lateralis muscle was directly measured using ultrasonography while the subjects performed ramp isometric knee extension up to MVC. The relationship between the estimated muscle force and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness of the tendon structures. The training increased significantly the volume (7.6±4.3%) and MVC torque (33.9±14.4%) of quadriceps femoris muscle. The L values at force production levels beyond 550 N were significantly shorter after training. The stiffness increased significantly from 67.5±21.3 to 106.2±33.4 N/mm. Furthermore, the training significantly increased the rate of torque development (35.8 ± 20.4%) and decreased electromechanical delay (-18.4±3.8%). Thus the present results indicate that isometric training increases the stiffness and Young's modulus of human tendon structures as well as muscle strength and size. This change in the tendon structures would be assumed to be an advantage for increasing the rate of torque development and shortening the electromechanical delay.
Effect of habitual running on human Achilles tendon load-deformation properties and cross-sectional area
Whether the cross-sectional area (CSA) and mechanical properties of the human Achilles tendon change in response to habitual exercise remains largely unexplored. The present study evaluated the CSA and contraction-induced displacement of the aponeurosis-tendon complex of the triceps surae in 11 untrained subjects before (tests 1 and 2) and after (test 3) ~9 mo of regular running (~78 training sessions). Displacement of the tendon-aponeurosis complex obtained by ultrasonography; electromyography of the gastrocnemius, soleus, and dorsiflexor muscles; and joint angular rotation were recorded during graded isometric plantarflexion ramps. Tendon CSA and moment arm were measured by using MRI, and tendon force was calculated from joint moments and tendon moment arm. A treadmill test was used to determine submaximal oxygen consumption (O2) at a given speed and maximal O2. The total running duration was ~43 h, distributed over 34 wk. Maximal O2 increased 8.6% (P < 0.01), and submaximal O2 decreased 6.2% (P < 0.05). Tendon-aponeurosis displacement during maximal voluntary contraction was unchanged (tests 1–3, 5.2 ± 0.6, 5.2 ± 0.5, and 5.3 ± 0.4 mm, respectively) and yielded a structural stiffness of 365 ± 50, 358 ± 40, and 384 ± 52 N/mm for tests 1–3, respectively (P > 0.05). Tendon CSA also remained unchanged (tests 1–3, 34.2 ± 2.2, 33.9 ± 2.2, and 33.8 ± 2.1 mm2, respectively). In conclusion, a total training stimulus of ~9 mo of running in previously untrained subjects was adequate to induce significant cardiovascular improvements, although it did not result in any changes in the mechanical properties of the triceps surea tendon-aponeurosis complex or in the dimensions of Achilles tendon.
Optimal muscle fascicle length and tendon stiffness for maximising gastrocnemius efficiency during human walking and running
Muscles generate force to resist gravitational and inertial forces and/or to undertake work, e.g. on the centre of mass. A trade-off in muscle architecture exists in muscles that do both; the fibres should be as short as possible to minimise activation cost but long enough to maintain an appropriate shortening velocity. Energetic cost is also influenced by tendon compliance which modulates the timecourse of muscle mechanical work. Here we use a Hill-type muscle model of the human medial gastrocnemius to determine the muscle fascicle length and Achilles tendon compliance that maximise efficiency during the stance phase of walking (1.2 m/s) and running (3.2 and 3.9 m/s). A broad range of muscle fascicle lengths (ranging from 45 to 70 mm) and tendon stiffness values (150–500 N/mm) can achieve close to optimal efficiency at each speed of locomotion; however, efficient walking requires shorter muscle fascicles and a more compliant tendon than running. The values that maximise efficiency are within the range measured in normal populations. A non-linear toe-region region of the tendon force–length properties may further influence the optimal values, requiring a stiffer tendon with slightly longer muscle fascicles; however, it does not alter the main results. We conclude that muscle fibre length and tendon compliance combinations may be tuned to maximise efficiency under a given gait condition. Efficiency is maximised when the required volume of muscle is minimised, which may also help reduce limb inertia and basal metabolic costs.
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On muscle, tendon and high heels
First published online July 16, 2010
Journal of Experimental Biology 213, 2582-2588 (2010)
Published by The Company of Biologists 2010
R. Csapo1,2,*, C. N. Maganaris1, O. R. Seynnes1 and M. V. Narici1
1 Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Faculty of Science and Engineering, John Dalton Building, Chester Street, Manchester, M1 5GD, UK
2 University of Vienna, Centre of Sport Sciences and University Sports, Department of Sports Medicine and Training Science, Auf der Schmelz 6, 1150 Vienna, Austria
* Author for correspondence (robert.csapo@univie.ac.at)
Accepted 26 April 2010
Wearing high heels (HH) places the calf muscle–tendon unit (MTU) in a shortened position. As muscles and tendons are highly malleable tissues, chronic use of HH might induce structural and functional changes in the calf MTU. To test this hypothesis, 11 women regularly wearing HH and a control group of 9 women were recruited. Gastrocnemius medialis (GM) fascicle length, pennation angle and physiological cross-sectional area (PCSA), the Achilles' tendon (AT) length, cross-sectional area (CSA) and mechanical properties, and the plantarflexion torque–angle and torque–velocity relationships were assessed in both groups. Shorter GM fascicle lengths were observed in the HH group (49.6±5.7 mm vs 56.0±7.7 mm), resulting in greater tendon-to-fascicle length ratios. Also, because of greater AT CSA, AT stiffness was higher in the HH group (136.2±26.5 N mm–1 vs 111.3±20.2 N mm–1). However, no differences in the GM PCSA to AT CSA ratio, torque–angle and torque–velocity relationships were found. We conclude that long-term use of high-heeled shoes induces shortening of the GM muscle fascicles and increases AT stiffness, reducing the ankle's active range of motion. Functionally, these two phenomena seem to counteract each other since no significant differences in static or dynamic torques were observed.