Comparison of viscoelastic characteristics in triceps surae between Black and White athletes.

The purpose of the present study was to investigate race differences in viscoelastic characteristics of triceps surae muscle group. Black and white college sprint type athletes (n=44) participated in this study. Viscoelastic properties were assessed using the free vibration technique: subjects sat with their forefeet on the edge of a force-plate (Kistler, Switzerland) and support a frame loaded with weights (0-40 kg) on the knees. Oscillations of the triceps surae and Achilles tendon system were initiated with a hand-held hammer by tapping the weight load. Oscillations occur at frequencies of 3-6 Hz and were slightly damped. The damped oscillations in conjunction with the equation of motion of a damped mass-spring model were used to calculate the viscosity of muscle (b), and the elasticity of muscle fibres (k(d)) and tendon (k(t)) in each subject. There were little significant differences in most of physical characteristic variables between black and white athletes. Black athletes have significantly greater muscle viscosity and elasticity than white athletes while tendon elasticity is equivalent. Thus, muscle stiffness is greater among black athletes. Greater muscle stiffness could contribute to greater sprint/jump performance among black athletes, compared with white athletes, through alteration of foot/ground contact and take-off phases during sprinting/jumping.

In vivo determination of muscle viscoelasticity in the human leg.

The purpose of this study was to examine the methodological validity of the free vibration technique for determining individual viscoelastic characteristics of the human triceps surae muscle-tendon complex (MTC) in vivo. Six subjects sat with first phalangeal joint of the forefoot on the edge of a force-plate. The special frame on the knee was loaded with weight (0-40 kg) for testing. Oscillations of the triceps surae MTC system were initiated with a hand-held hammer by tapping the weight. In order to keep the same posture, the output of the force plate was displayed on the oscilloscope and subjects were asked to maintain the beam on the oscilloscope at a particular location in relation to a reference line. The damped oscillations in conjunction with the equation of motion of a damped mass-spring model were used to calculate the viscosity of muscle (b) and the elasticity of muscle fibres and tendon (k) in each subject, considering moment arm of the ankle joint. With this arrangement, we have obtained high reproducibility in this method. The coefficient of variations (CVs) of b and k in five trials at each weight were quite small (range: 0.5-18.7% in b and 1.0-15.1% in k). There were no significant differences in viscoelastic coefficients between right and left legs. Therefore, it appears that free vibration technique, used here, is adequate in describing the viscoelastic characteristics of the triceps surae in vivo in humans.

Relationship between sprint performance and muscle fascicle length in female sprinters.

The purpose of this study was to investigate the relationship between sprint performance and architectural characteristics of leg muscles in 26 female 100-m sprinters. Pennation angle and muscle thickness of the vastus lateralis (VL) and gastrocnemius medialis (GM) and lateralis (GL) muscles were measured by B-mode ultrasonography, and fascicle length was estimated. Sprinters had a significantly lower VL pennation angle, but GM and GL pennation angle was similar between sprinters and female control subjects (N = 22). There was no significant correlation between pennation angle and 100-m personal best performance. Sprinters had significantly greater absolute fascicle length in VL and GL than controls, which significantly correlated to 100-m best-record (r = -0.51 and r = -0.44, respectively). Relative fascicle length (VL and GL) were also significantly greater in sprinters than controls. However, there were no significant correlation between relative fascicle length and 100-m best-record (r = -0.36 and r = -0.29, respectively). No relationship was found between the sprint performance and fat-free mass (r = -0.26) or body mass index (r = -0.03). However, there was a significant correlation between percent (%) body fat and 100-m best-record (r = 0.62, p < 0.01). Adjusting the confounding effect of % fat, significant correlations were seen between relative fascicle length and 100-m best-record (VL; r = -0.39 and GL; r = -0.40). Absolute and relative fascicle length were similar in elite female sprinters compared with previous reported values for elite male sprinters (Kumagai et al., 2000). It was concluded that longer fascicle length is associated with greater sprinting performance in sprinters, but there is no gender differences in fascicle length for elite sprinters.

Behavior of fascicles and tendinous structures of human gastrocnemius during vertical jumping.

Behavior of fascicles and tendinous structures of human gastrocnemius medialis (MG) was determined by use of ultrasonography in vivo during jumping. Eight male subjects jumped vertically without countermovement (squat jump, SQJ). Simultaneously, kinematics, kinetics, and electromyography from lower leg muscles were recorded during SQJ. During phase I (-350 to -100 ms before toe-off), muscle-tendon complex (MTC) length was almost constant. Fascicles, however, shortened by 26%, and tendinous structures were stretched by 6%, storing elastic energy of 4.9 J during phase I. During phase II (-100 ms to toe-off), although fascicles generated force quasi-isometrically, MTC shortened rapidly by 5.3%, releasing prestored elastic energy with a higher peak positive power than that of fascicles. Also, the compliance of tendinous structures in vivo was somewhat higher than that of external tendon used in the simulation studies. The results demonstrate that the compliance of tendinous structures, together with no yielding of muscle fibers, allows MTC to effectively generate relatively large power at a high joint angular velocity region during the last part of push-off.

In vivo behaviour of human muscle tendon during walking.

In the present study we investigated in vivo length changes in the fascicles and tendon of the human gastrocnemius medialis (GM) muscle during walking. The experimental protocol involved real-time ultrasound scanning of the GM muscle, recording of the electrical activity of the muscle, measurement of knee- and ankle-joint rotations, and measurement of ground reaction forces in six men during walking at 3 km h(-1) on a treadmill. Fascicular lengths were measured from the sonographs recorded. Musculotendon complex length changes were estimated from anatomical and joint kinematic data. Tendon length changes were obtained combining the musculotendon complex and fascicular length-change data. The fascicles followed a different length-change pattern from those of the musculotendon complex and tendon throughout the step cycle. Two important features emerged: (i) the muscle contracted near-isometrically in the stance phase, with the fascicles operating at ca. 50 mm; and (ii) the tendon stretched by ca. 7 mm during single support, and recoiled in push-off. The behaviour of the muscle in our experiment indicates consumption of minimal metabolic energy for eliciting the contractile forces required to support and displace the body. On the other hand, the spring-like behaviour of the tendon indicates storage and release of elastic-strain energy. Either of the two mechanisms would favour locomotor economy

In vivo dynamics of human medial gastrocnemius muscle-tendon complex during stretch-shortening cycle exercise.

The purpose of this study was to investigate the dynamics of human muscle-tendon complex (MTC) during stretch-shortening cycle exercises through in vivo observation. A total of seven male subjects performed dorsi flexion followed by plantar flexion at two different frequencies, 0.3 Hz (slow) and 1.0 Hz (fast), in a toe-standing position. The fascicle length (LF) of the medial gastrocnemius muscle during the movements was determined using a real-time ultrasonography in vivo. The LF at the switching phase from dorsi to plantar flexion was significantly shorter in the fast exercise (54.4 +/- 5.5 mm) than in the slow one (58.2 +/- 5.4 mm), suggesting that the elongation of tendon structures at that time was significantly greater in the former than in the latter. Furthermore, at the initial stage of plantar flexion during the fast movement, the LF hardly changed with a rapid shortening of tendon structures at that time. The observed relation between MTC length and force showed that the behaviour of tendon structures contributed to 20.2 and 42.5% of the total amount of work completed during plantar flexion phase in the slow and fast movements, respectively. Thus, the present results suggest that tendon structures make the dynamics of MTC more efficient during stretch-shortening cycle exercises by changing their lengths.

A sensitivity analysis of the calculation of mechanical output through inverse dynamics: a computer simulation study.

The purpose of this study was to systematically determine the effect of experimental errors on the work output calculated using two different methods of inverse dynamics during vertical jumping: (a) the conventional (rotational) method and (b) the translational method. A two-dimensional musculoskeletal model was used to generate precisely known kinematics. Next, the location of each joint center (JC) and the location of each segment's center of mass (CM) were manipulated by +/-10% of segment length to simulate errors in the location of joint centers (delta JC) and errors in the location of segment's center of mass (delta CM), respectively. Work output was subsequently calculated by applying the two methods of inverse dynamics to the manipulated kinematic data. The results showed that the translational method of inverse dynamics was less sensitive (up to 13% error in total work output) to delta JC and delta CM than the rotational method (up to 28% error in total work output). The rotational method of inverse dynamics was particularly sensitive to simulated errors in JC.

Comparison of new approaches to estimate mechanical output of individual joints in vertical jumps.

Conventional calculation of joint power is not effective in order to assess translational motions of human body. Two new approaches were developed in this study to estimate translational mechanical outputs from individual joints. They were applied to the analysis of vertical jump motions of six male subjects. In both cases, body of subjects were modeled with a four mass-points system model, and joints were regarded as motion generators. In one approach, increase of vertical component of ground reaction force (GRF) was decomposed into push-off force of three joints (ankle, knee, and hip joints). This procedure gave an estimation of impulse exerted per leg, as 83-92 N s (95% confidential interval) for squat jump, which was similar to half of the impulse provided to mass center of the body calculated from GRF, 82-88 N s. In the other approach, amount of the power exerted by each joint vertically was estimated by calculating the scalar product of joint reaction force and relative velocity vectors of adjacent segments. This approach gave estimation of vertical work provision per leg, as 201-226 and 141-181 J for squat and counter movement jumps, which were not so different from half of the work provided to mass center of the body calculated from GRF, 209-227 and 137-175 J, respectively. As these approaches make it possible to calculate translational mechanical outputs specifically, they are useful and consistent concerning the analysis of translational motion of human body.

Nonisometric behavior of fascicles during isometric contractions of a human muscle.

Fascicle length, pennation angle, and tendon elongation of the human tibialis anterior were measured in vivo by ultrasonography. Subjects (n = 9) were requested to develop isometric dorsiflexion torque gradually up to maximal at the ankle joint angle of 20 degrees plantarflexion from the anatomic position. Fascicle length shortened from 90 +/- 7 to 76 +/- 7 (SE) mm, pennation angle increased from 10 +/- 1 to 12 +/- 1 degrees, and tendon elongation increased up to 15 +/- 2 mm with graded force development up to maximum. The tendon stiffness increased with increasing tendon force from 10 N/mm at 0-20 N to 32 N/mm at 240-260 N. Young's modulus increased from 157 MPa at 0-20 N to 530 MPa at 240-260 N. It can be concluded that, in isometric contractions of a human muscle, mechanical work, some of which is absorbed by the tendinous tissue, is generated by the shortening of muscle fibers and that ultrasonography can be used to determine the stiffness and Young's modulus for human tendons.

The side-to-side differences of bone mass at proximal femur in female rhythmic sports gymnasts.

This cross-sectional study examined the side-to-side differences of the bone mineral density (BMD) at proximal femora in female rhythmic sports gymnasts (RSGs). The hypothesis on which the study is based is that gymnasts use a different leg in take-off (left leg) and in landing (right leg) and therefore differ in the loading for the left and right legs. The gymnasts made up two groups: the regular group, which consisted of 15 regular players who had trained for about 28 h/week, and the substitutes group, which consisted of 8 substitute players who had trained for about 12 h/week. The control group consisted of 10 nonathletic college women who had not participated in any kind of regular sports activity. BMD (g/cm2) was measured in three hip sites using the XR-26 dual-energy X-ray absorptiometer scanner. Muscle strength at knee extensors (EXT) and flexors (FLX) was examined using an isokinetic dynamometer (CYBEX6000), and the vertical ground reaction force was determined with a force platform during take-off and landing movements. In the regular players, the BMDs of the left leg were significantly higher than those of the right leg at the femoral necks, greater trochanters, and Ward's triangles (p < 0.01 to approximately 0.005). The side-to-side differences were 4.7 to approximately 9.6%. Regarding the strength parameters, the left side was greater than the right side significantly at EXT 60 degrees/s (p < 0.01), although the overall side-to-side difference was small. In the substitutes, the BMDs at the three sites mentioned above were also higher in the left leg than the right, but the side-to-side difference was statistically significant only at Ward's triangles (93%, p < 0.05). The side-to-side difference of strength was not significant. In the controls, there were small left-to-right differences of the BMDs, ranging from -1.8 to 0.5%, which was significantly lower than in the regular players at each site. The overall average strength measurements were larger in the right leg than in the left except at the 120 degrees/s. The side-to-side difference was statistically significant at EXT 30 degrees/s and 60 degrees/s (p < 0.05). The peak force was greater in take-off than in landing, and the unit time force during take-off was significantly greater than that during landing (p < 0.001). In conclusion, regarding the side-to-side difference of the BMD at proximal femora, our results demonstrate: that the left leg for take-off had higher measurements than the right leg for landing in both gymnasts' groups, which accounts for the vertical ground reaction force during take-off being greater than that during landing; that the difference in the regular players group was greater than that in the substitute group, which can be explained because the regular players practiced much more than the substitutes did; and that there was no difference in the control group.

Muscle architecture and function in humans.

The present study focused on architectural factors which are considered to influence the linkage of muscle fiber and joint actions. By means of real-time ultrasonography we can observe clearly and noninvasively in vivo the movement of fascicle and aponeurosis in human muscle and measure directly the changes in pennation angle and length of fascicle during muscle contraction. During dorsi and plantar flexion without load the movement of tendinous tissue in human tibialis anterior muscle (TA) appeared to synchronize with the displacement of the ankle joint, indicating that the muscle tendon complexes are stiff relative to the applied force, which is fairly small in the case of foot shaking motion. On the other hand, when the ankle joint was fixed and the TA contracted 'statically' the ultrasonic echo from deep aponeurosis in the TA was observed to move proximally, indicating the elastic component (i.e. mainly tendinous tissue) was stretched significantly by the contraction force of muscle. In the case of the kneejoint, a length of fascicle in vastus lateralis decreased by 18% with the extension of the knee passively from a 100 degrees flexed position. When the knee extensors contracted 'statically' the fascicle length decreased at every joint angles and its magnitude was greater (30%) when the knee was closer to full extension than (5%) at the flexed positions. The present results clearly show that the architecture of actively contracting muscle fibers differ considerably than that which occurs when movement is passively induced. The use of cadaver data in the study of architecture and modeling of muscle functions would result in inaccurate, and in some cases even erroneous results.

Determination of fascicle length and pennation in a contracting human muscle in vivo.

We have developed a technique to determine fascicle length in human vastus lateralis muscle in vivo by using ultrasonography. When the subjects had the knee fully extended passively from a position of 110 degree flexion (relaxed condition), the fascicle length decreased from 133 to 97 mm on average. During static contractions at 10% of maximal voluntary contraction strength (tensed condition), fascicle shortening was more pronounced (from 126 to 67 mm), especially when the knee was closer to full extension. Similarly, as the knee was extended, the angle of pennation (fascicle angle, defined as the angle between fascicles and aponeurosis) increased (relaxed, from 14 to 18 degrees; tensed, from 14 to 21 degrees), and a greater increase in the pennation angle was observed in the tensed than in the relaxed condition when the knee was close to extension (< 40 degrees). We conclude that there are differences in fascicle lengths and pennation angles when the muscle is in a relaxed and isometrically tensed conditions and that the differences are affected by joint angles, at least at the submaximal contraction level.

Tendinous movement of a human muscle during voluntary contractions determined by real-time ultrasonography.

The degree of shortening or lengthening of muscles during joint actions has not been clarified in humans, although such information is essential in understanding human muscle functions. In this study, the tendinous movement of a muscle was determined by real-time ultrasonography during voluntary contractions. The tibialis anterior muscle (TA) was tested in five healthy men who performed dorsi- and plantar flexion movements (shortening and lengthening of TA) at two frequencies (0.1 and 1.5 Hz). The insertion point (eta) of fascicles onto the aponeurosis was clearly visualized on the ultrasonogram, and its position relative to a fixed marker moved proximally and distally according to dorsi- and plantar flexion of ankle joint. The movement of eta occurred in phase with the angular change of ankle joint, giving high correlations (r = 0.93 to 0.97) between the displacement of eta and the angle. The displacement of eta for one radian of joint angle change, 46.5 +/- 1.7 (SD) mm, was comparable to the reported moment arm of TA. The present method has many potential applications in the field of muscle physiology and biomechanics in humans.

In vivo Achilles tendon loading during jumping in humans.

Elastic behaviour of the human tendomuscular system during jumping was investigated by determination of the in vivo Achilles tendon force. A buckle-type transducer was implanted under local anaesthesia around the right Achilles tendon of an adult subject. After calibration, the Achilles tendon force was recorded together with the triceps surae muscle electromyogram activity and high speed filming and ground reaction force during: a maximal vertical jump from a squat position, a maximal vertical jump from an erect standing position with a preliminary counter-movement, and repetitive submaximal hopping on the spot. Jumping heights were 33, 40 and 7 cm in the squat, the counter movement and the hopping positions, respectively. The peak Achilles tendon force and mechanical work by the calf muscles were 2233 N and 34 J in the squat jump, 1895 N and 27 J in the counter movement jump, and 3786 N and 51 J when hopping. The changes in tendon length were estimated assuming a stiffness constant calculated from the tendon architecture. The percentages of elastic energy stored in the Achilles tendon during jumping were 23%, 17% and 34% of the total calf muscle work in the squat jump, the counter movement jump, and hopping, respectively.

Ultrasonography gives directly but noninvasively elastic characteristic of human tendon in vivo.

To obtain an insight into tendon elasticity during human movement, a real-time ultrasonography was applied to the contracting tibialis anterior muscle. The insertion point of fascicles onto the aponeurosis was clearly visualized, and its position relative to a fixed marker on the skin moved proximally (delta 1) according to the increasing dorsiflexion force (delta F) with a fixed ankle joint. Notably, the delta 1-delta F relationship in the tendon was found to be quadratic in nature (delta F = c delta 1(2); c = 1.48-2.24, r = 0.985-0.992, n = 9) as has been reported in the isolated tendon, although the delta F-delta 1 curves were slightly underestimated in comparison with the stiffness constant estimated from tendon architecture. This underestimation might be caused by changes in the height of the foot arch with the application of force.

Comparison between the directly measured achilles tendon force and the tendon force calculated from the ankle joint moment during vertical jumps.

UNLABELLED: The purpose of this study was to compare the relationship between the achilles tendon force and the tendon force estimated from the ankle joint moment (EATF) during vertical jump. A healthy male subject performed the following jumps on the force platform: (a) maximal vertical jump from a squat position without counter-movement; (b) maximal vertical jump from an erect standing position with a preliminary counter-movement; (c) repetitive submaximal hopping on the spot with preferred frequency. The achilles tendon force was measured directly with an implanted tendon transducer in all jumping conditions. In addition the joint moment obtained from the film and ground reaction force was used to estimate the tendon force. Measurements revealed that the achilles tendon sustained high loads during the vertical jumps. The peak values of the real achilles tendon forces were 2234 N, 1896 N, and 3787 N in the squatting, the counter-movement, and the hopping jumps respectively. The achilles tendon forces were about twice the ground reaction force. The estimated achilles tendon force showed almost the same impulses with actual force, especially during hopping. However, estimated force overestimated the actual force during the early plantarflexion phase of jumping and the maximal error of the estimation was relatively large. RELEVANCE: The direct measurement of the achilles tendon forces during human movement may open ways to better understanding of the mechanisms of muscle function. Its clinical importance can be seen in its possibility to reveal the true loading characteristics of the muscle-tendon complex in almost any movement situation, including those which are expected to cause injury. The findings can be used for estimation of the true tendon forces from the method of inverse dynamics.

Biomechanical loading of Achilles tendon during normal locomotion.

Direct in vivo Achilles tendon force measurements open up new possibilities for understanding the loading of the Achilles tendon during natural locomotion. This article describes how these human experiments can be performed. The results of these experiments imply that Achilles tendon forces are unexpectedly high in certain activities (e.g., hopping) and that the rates of loading rather than the absolute magnitudes of the recorded forces may be more relevant for clinical purposes as well as for the construction of artificial tendon materials.

Joint moment and mechanical power flow of the lower limb during vertical jump.

The purpose of this study was to examine the joint moment and the mechanical power flow in the lower limb during three types of vertical jump. A healthy male subject performed the following jumps: maximal vertical jump from a squatting position (SJ), maximal vertical jump from an erect standing position with a preliminary countermovement (CMJ), and repetitive submaximal hopping in place with preferred frequency. The jumps on the force plate were also filmed (100 frames X s-1). Film analysis on force platform records were used to obtain the joint reaction forces, moments, mechanical powers, and work. All the peak values of moments of CMJ were greater than those of SJ, but in both cases they appeared in the same rank order (hip greater than knee greater than ankle). The mechanical work of the hip extensors was much greater than that of SJ although the work by the knee extensors and the ankle plantar flexors was almost the same in these jumps. It was suggested that the performance difference between SJ and CMJ might result from the difference in work by the hip extensors rather than from the effect of the stored elastic energy. Hopping differed from SJ and CMJ and was characterized by large moment and mechanical work of the ankle plantar flexors. The results also suggest that muscle elasticity may play a greater role in hopping than in CMJ.

An estimation of the velocities of three take-off phases in 18-m triple jump.

The purposes of this study were to estimate the take-off velocities necessary to gain a given distance on the triple jump by adopting three hypotheses and to investigate the external force vectors during the jump's supporting phase. The total distance corresponding to the varying combinations of horizontal and vertical velocities at take-offs were calculated based on these hypotheses. The calculated velocities of the body's center of gravity coincided well with the observed total distance, even though the velocities were slightly underestimated. There was a significant correlation between the run-up velocity and the total distance (r = 0.91, P less than 0.001). From these results, the run-up and take-off velocities and the external force vectors for an 18-m jump were estimated. It might be said that the 18-m jumper must gain great run-up velocity (10.7 m X s-1) and exert forces during each supporting phase which are 3.6-4.4 times the body weight, resulting in a force-vector angle of about 101 degrees at each take-off.

A biomechanical study of the triple jump.

The purpose of this study was to investigate the triple jump from the viewpoint of the velocity of the center of gravity and the mechanical energy. Eight 16 mm cameras were used to film the whole motion of 15 triple-jumpers from the end of the run-up to the landing of the jump. The horizontal velocity decreased during the first half of each take-off and increased during the second half. However, the absolute value of the velocity decreased from hop-to-step and from step-to-jump (the reductions were 8.5% and 15.1%, respectively). The vertical velocity increased at an almost constant rate during each take-off. The maximum height of the center of gravity was similar during the flights in the hop and the jump, and in the step it was approximately 10% lower than in the hop and the jump. The mechanical energy decreased after each take-off. Four percent of the mechanical energy acquired during the run-up was lost during take-off for the hop. The maintenance ratio was much lower (approximately 85%) for the step and the jump.