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Gerrit Jan van Ingen Schenau, Maarten F. Bobbert, and Arnold de Haan

This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch-shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch-shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanics and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves under in-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.

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Saied Jalal Aboodarda, Ashril Yusof, N.A. Abu Osman, Martin W. Thompson, and A. Halim Mokhtar

Purpose:

To identify the effect of additional elastic force on the kinetic and kinematic characteristics, as well as the magnitude of leg stiffness, during the performance of accentuated countermovement jumps (CMJs).

Methods:

Fifteen trained male subjects performed 3 types of CMJ including free CMJ (FCMJ; ie, body weight), ACMJ-20, and ACMJ-30 (ie, accentuated eccentric CMJ with downward tensile force equivalent to 20% and 30% body mass, respectively). A force platform synchronized with 6 high-speed infrared cameras was used to measure vertical ground-reaction force (VGRF) and displacement.

Results:

Using downward tensile force during the lowering phase of a CMJ and releasing the bands at the start of the concentric phase increased maximal concentric VGRF (6.34%), power output (23.21%), net impulse (16.65%), and jump height (9.52%) in ACMJ-30 compared with FCMJ (all P < .05). However, no significant difference was observed in the magnitude of leg stiffness between the 3 modes of jump. The results indicate that using downward recoil force of the elastic material during the eccentric phase of a CMJ could be an effective method to enhance jump performance by applying a greater eccentric loading on the parallel and series elastic components coupled with the release of stored elastic energy.

Conclusions:

The importance of this finding is related to the proposition that power output, net impulse, takeoff velocity, and jump height are the key parameters for successful athletic performance, and any training method that improves impulse and power production may improve sports performance, particularly in jumping aspects of sport.

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Alberto Minetti, Marco Narici, and Paolo Cerretelli

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Bruce C. Elliott, Kevin G. Baxter, and Thor F. Besier

This research examined the influence on performance of no-pause and mean delays of 0.97 s and 1.5 s between the eccentric and concentric phases of the stretch-shorten cycle movement of internal rotation (IR) of me upper arm. Videography and surface electromyography were used in the assessment of 19 athletes throwing a baseball in a manner that constrained all degrees of freedom other than upper-arm IR. Results demonstrated that the pectoralis major, latissimus dorsi, and anterior deltoid muscles were all active at above 100% maximum voluntary contraction (MVC) during IR. The maximum velocity of the wrist decreased with increasing pause time between me eccentric and concentric phases of the IR movement. A mean 21.9% augmentation to the maximum wrist velocity was recorded when the no-pause delay and a mean delay of 1.5 s were compared. There were no electromyographically discernible differences recorded either prior to or after release for any of the monitored muscles during IR across the pause conditions. It is evident therefore that the benefits of a prestretch during external rotation (ER) have a significant influence on the subsequent velocity of IR.

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Tomonari Takeshita, Hiroaki Noro, Keiichiro Hata, Taira Yoshida, Tetsuo Fukunaga, and Toshio Yanagiya

half of the stance phase, while running, the muscle–tendon units (MTU) of the ankle plantar flexors are lengthened, whereas they are shortened in the second half of the stance phase. 11 , 12 It is therefore considered that elastic energy is stored in the MTUs of plantar flexors due to the negative

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Laurence Houghton, Brian Dawson, and Jonas Rubenson

Effects of prolonged running on Achilles tendon properties were assessed after a 60 min treadmill run and 140 min intermittent shuttle running (simulated cricket batting innings). Before and after exercise, 11 participants performed ramp-up plantar flexions to maximum-voluntary-contraction before gradual relaxation. Muscle-tendon-junction displacement was measured with ultrasonography. Tendon force was estimated using dynamometry and a musculoskeletal model. Gradients of the ramp-up force-displacement curves fitted between 0–40% and 50–90% of the preexercise maximal force determined stiffness in the low- and high-force-range, respectively. Hysteresis was determined using the ramp-up and relaxation force-displacement curves and elastic energy storage from the area under the ramp-up curve. In simulated batting, correlations between tendon properties and shuttle times were also assessed. After both protocols, Achilles tendon force decreased (4% to 5%, P < .050), but there were no changes in stiffness, hysteresis, or elastic energy. In simulated batting, Achilles tendon force and stiffness were both correlated to mean turn and mean sprint times (r = −0.719 to −0.830, P < .050). Neither protocol resulted in fatigue-related changes in tendon properties, but higher tendon stiffness and plantar flexion force were related to faster turn and sprint times, possibly by improving force transmission and control of movement when decelerating and accelerating.

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Harald Böhm, Gerald K. Cole, Gert-Peter Brüggemann, and Hanns Ruder

The contribution of muscle in-series compliance on maximum performance of the muscle tendon complex was investigated using a forward dynamic computer simulation. The model of the human body contains 8 Hill-type muscles of the lower extremities. Muscle activation is optimized as a function of time, so that maximum drop jump height is achieved by the model. It is shown that the muscle series elastic energy stored in the downward phase provides a considerable contribution (32%) to the total muscle energy in the push-off phase. Furthermore, by the return of stored elastic energy all muscle contractile elements can reduce their shortening velocity up to 63% during push-off to develop a higher force due to their force velocity properties. The additional stretch taken up by the muscle series elastic element allows only m. rectus femoris to work closer to its optimal length, due to its force length properties. Therefore the contribution of the series elastic element to muscle performance in maximum height drop jumping is to store and return energy, and at the same time to increase the force producing ability of the contractile elements during push-off.

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Shane R. Wurdeman, Jessie M. Huisinga, Mary Filipi, and Nicholas Stergiou

Patients with multiple sclerosis (MS) have less-coordinated movements of the center of mass resulting in greater mechanical work. The purpose of this study was to quantify the work performed on the body’s center of mass by patients with MS. It was hypothesized that patients with MS would perform greater negative work during initial double support and less positive work in terminal double support. Results revealed that patients with MS perform less negative work in single support and early terminal double support and less positive work in the terminal double support period. However, summed over the entire stance phase, patients with MS and healthy controls performed similar amounts of positive and negative work on the body’s center of mass. The altered work throughout different periods in the stance phase may be indicative of a failure to capitalize on passive elastic energy mechanisms and increased reliance upon more active work generation to sustain gait.

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Stéphane Perrey, Guillaume Millet, Robin Candau, and Jean-Denis Rouillon

The purpose of this study was to examine the effects of speed on the stretch-shortening cycle (SSC) behavior during roller ski skating. Ten highly skilled male cross-country skiers roller skied at 4.56, 5.33 m · s–1 and maximal speed using the V2-alternate technique on a flat terrain. Knee and ankle joint kinematics, and EMG of the vastus lateralis (VL) and gastrocnemius lateralis (GL) muscles were recorded during the last 40 s of each bout of roller skiing. Maximal speed was associated with increases in cycle rate combined with decreases in cycle length. For VL, no significant differences were observed for the integrated EMG eccentric-to-concentric ratio (iEMG Ecc/Conc) and for the stretching velocity over the range of speeds. For GL, stretching velocity and iEMG Ecc/Conc were significantly greater at maximal speed. The analysis of GL EMG activity suggests that speed improved GL stiffness so that more elastic energy was stored, a better force transmission occurred, and coupling time decreased. These findings suggest that the efficiency of roller ski skating locomotion may be increased with speed through a better use of the stretch-shortening cycle pattern in the ankle extensors.