Toshimasa Yanai

Nonuniform Muscle Hypertrophy: Its Relation to Muscle Activation in Training Session

PURPOSE Muscle hypertrophy in response to resistance training has been reported to occur nonuniformly along the length of the muscle. The purpose of the present study was to examine whether the regional difference in muscle hypertrophy induced by a training intervention corresponds to the regional difference in muscle activation in the training session. METHODS Twelve young men participated in a training intervention program for the elbow extensors with a multijoint resistance exercise for 12 wk (3 d · wk(-1)). Before and after the intervention, cross-sectional areas of the triceps brachii along its length were measured with magnetic resonance images. A series of transverse relaxation time (T2)-weighted magnetic resonance images was recorded before and immediately after the first session of training intervention. The T2 was calculated for each pixel within the triceps brachii. In the images recorded after the session, the number of pixels with a T2 greater than the threshold (mean + 1 SD of T2 before the session) was expressed as the ratio to the whole number of pixels within the muscle and used as an index of muscle activation (percent activated area). RESULTS The percent activated area of the triceps brachii in the first session was significantly higher in the middle regions than that in the most proximal region. Similarly, the relative change in cross-sectional area induced by the training intervention was also significantly greater in the middle regions than the most proximal region. CONCLUSION The results suggest that nonuniform muscle hypertrophy after training intervention is due to the region-specific muscle activation during the training session.

Rotational effect of buoyancy in frontcrawl: does it really cause the legs to sink?

The purposes of this study were to quantify the rotational effect of buoyant force (buoyant torque) during the performance of front crawl and to reexamine the mechanics of horizontal alignment of the swimmers. Three-dimensional videography was used to measure the position and orientation of the body segments of 11 competitive swimmers performing front crawl stroke at a sub-maximum sprinting speed. The dimensions of each body segment were defined mathematically to match the body segment parameters (mass, density, and centroid position) reported in the literature. The buoyant force and torque were computed for every video-field (60fields/s), assuming that the water surface followed a sine curve along the length of the swimmer. The average buoyant torque over the stroke cycle (mean=22Nm) was directed to raise the legs and lower the head, primarily because the recovery arm and a part of the head were lifted out of the water and the center of buoyancy shifted toward the feet. This finding contradicts the prevailing speculation that buoyancy only causes the legs to sink throughout the stroke cycle. On the basis of a theoretical analysis of the results, it is postulated that the buoyant torque, and perhaps the forces generated by kicks, function to counteract the torque generated by the hydrodynamic forces acting on the hands, so as to maintain the horizontal alignment of the body in front crawl.

Effect of pressure intensity of graduated elastic compression stocking on muscle fatigue following calf-raise exercise

The purpose of the present study was to examine the effects of wearing a graduated elastic compression (EC) stocking, with different pressure profiles during a fatiguing calf-raise exercise session, on the torque generating capacity after exercise. Fourteen subjects performed 15 sets of 10 repetitions of calf-raise exercise, wearing one of three stockings of different compression pressure profiles: two kinds of EC stockings (one (EC30) with 30mmHg at the ankle, 21-25mmHg at the calf, and 10mmHg below the knee, and the other (EC18) with 18, 12-14, and 7mmHg at the same regions, respectively) and a non-EC sport stocking as a control (CON). Before and after the exercise, torque and electromyographic (EMG) signals of medial gastrocnemius and soleus muscles were recorded during an evoked triplet contraction and the maximal voluntary contraction (MVC). All stockings had no effect on the decline of the MVC torque whereas the reduction of the evoke triplet torque in EC30 stocking condition was significantly smaller compared with that in CON (-6.4±8.5% for EC30 and -16.5±9.0% for CON, P<0.05). The reduction of the mean power frequency of EMG during MVC in the EC30 condition was significantly smaller than that in CON (-4.4±10.9Hz for EC30 and -18.7±7.9Hz for CON, P<0.05). These results suggest that the EC stocking with adequate pressure at the calf region relieves muscle fatigue of the triceps surae induced by calf-raise exercise.

In vivo determination of the Achilles tendon moment arm in three-dimensions

Two-dimensional methods have been applied to determine the Achilles tendon moment arm in previous studies, although the talocrural joint rotates in three-dimension. The purpose of this study was to develop a method for determining the Achilles tendon moment arm in three-dimensions (3DMA). A series of sagittal ankle images were obtained at ankle positions of -20°, -10° (dorsiflexed position), 0° (neutral position), +10°, +20°, and +30° (plantarflexed position). The talocrural joint axis was determined as the finite helical axis of the ankle joint over 20° of displacement, and the 3DMA was determined as the shortest distance from the talocrural joint axis to the line of action of the Achilles tendon force. The corresponding 2DMA was determined with the center of rotation method using the images captured on the sagittal plane passing through the mid-point of the medio-lateral width of the tibia. The 3DMA ranged from 35 to 41 mm across various ankle positions and was, on average, 11 mm smaller than 2DMA. The difference between the two measures was attributable primarily to the deviations of the talocrural joint axis from the anatomical medio-lateral direction. The deviations on the coronal plane (21.4±20.7°) and on the transverse planes (14.8±22.6°) accounted for the errors of 1.3 mm and 3.0 mm, respectively. In addition, selecting either a medially or laterally misaligned sagittal-plane image for determining the 2DMA gave rise to error by 3.5 mm. The remaining difference was accounted for by the random measurement error.

Twitch potentiation induced by stimulated and voluntary isometric contractions at various torque levels in human knee extensor muscles.

The purpose of this study was to compare the extent of twitch potentiation (TP) after stimulated or voluntary contractions at identical intensities for the human knee extensor muscles. Isometric knee extensions of 10 s were performed at 20%, 40%, and 60% of maximal voluntary contraction (MVC) torque level, through percutaneous electrical stimulation of the quadriceps at 80 Hz or voluntary contraction. Twitch responses were evoked by stimulating the femoral nerve percutaneously with supramaximal intensity. The extent of TP after the stimulated contraction was greater than that after the voluntary contraction at the 20% MVC torque level, whereas a stimulated contraction induced a smaller extent of TP than did a voluntary contraction at contraction intensities higher than 40% MVC. We suggest that this contraction intensity dependence of differences in TP after stimulated and voluntary isometric conditioning contractions is responsible for differences in the recruitment pattern of motor units during the conditioning contractions. Muscle Nerve, 2011

Triceps surae muscle–tendon unit length changes as a function of ankle joint angles and contraction levels: The effect of foot arch deformation

The purpose of this study was to clarify how foot deformation affects the relationship between triceps surae muscle-tendon unit (MTU) length and ankle joint angle. For six women and six men a series of sagittal magnetic resonance (MR) images of the right foot were taken, and changes in MTU length (the displacement of the calcaneal tuberosity), foot arch angle, and ankle joint angle were measured. In the passive session, each subjects ankle joint was secured at 10° dorsiflexed position, neutral position (NP), and 10° and 20° plantar flexed positions while MR images were acquired. In the active session, each subject was requested to perform submaximal isometric plantar flexions (30%, 60%, and 80% of voluntary maximum) at NP. The changes in MTU length in each trial were estimated by two different formulae reported previously. The changes of the measured MTU length as a function of ankle joint angles observed in all trials of the active session were significantly (p<0.05) larger than corresponding values in the passive session and by the estimation formulae. In the passive session, MTU length changes were significantly smaller than the estimated values when the ankle was plantar flexed. The foot arch angle increased as the contraction level increased from rest (117 ± 4°) to 80% (125 ± 3°), and decreased as the ankle was positioned further into plantar flexion in the passive session (115 ± 3°). These results indicate that foot deformation profoundly affects the triceps surae MTU length-ankle joint angle relationship during plantar flexion.

Effect of conditioning contraction intensity on postactivation potentiation is muscle dependent

We aimed to examine whether the influence of conditioning contraction intensity on the extent of postactivation potentiation (PAP) is muscle dependent. Eleven healthy males performed both thumb adduction and plantar flexion as a conditioning contraction. The conditioning contraction intensities were set at 20%, 40%, 60%, 80%, or 100% of the maximal voluntary isometric contraction (MVC). Before and after the conditioning contraction, twitch torque was measured for the respective joint to calculate the extent of PAP. In plantar flexion, the extent of PAP became significantly larger as the conditioning contraction intensity increased up to 80% MVC (p<0.05). In contrast, the extent of PAP in thumb adduction increased significantly only up to 60% MVC (p<0.05), but not at higher intensities. These results indicate that the influence of the conditioning contraction intensity on the extent of PAP is muscle dependent. Our results suggest that a conditioning contraction with submaximal intensity can sufficiently evoke sizable PAP in the muscle where most of muscle fibers are recruited at submaximal intensities, thereby attenuating muscle fatigue induced by the conditioning contraction.

Scapular Rotation to Attain the Peak Shoulder External Rotation in Tennis Serve

PURPOSE The purposes of this study were (a) to describe the detailed movements of the shoulder complex during the cocking phase in tennis serve and (b) to determine the contribution of the scapular rotation to the peak shoulder external rotation attained at the end of the cocking phase. METHOD Twenty tennis players performed flat tennis serves with the maximum effort, and three-dimensional kinematic data of the thorax, scapula, and humerus of the dominant side were recorded by an electromagnetic tracking device (Liberty; Polhemus) at 240 Hz. The humeral rotation with respect to the thorax (named as the resultant shoulder rotation) was decomposed into the scapular rotation with respect to the thorax and the humeral rotation with respect to the scapula (named as the glenohumeral rotation). The scapular rotation that contributed to attain the peak resultant shoulder external rotation was quantitatively determined, and the ratio of the glenohumeral external rotation to the scapular rotation that contributed to attain the peak resultant shoulder external rotation was computed to represent the scapulohumeral rhythm for shoulder external rotation. RESULTS Of the three components of scapular rotations, the scapular posterior tilt was the primary component that contributed to the attainment of the peak resultant shoulder external rotation. The scapulohumeral rhythm for shoulder external rotation (scapular posterior tilt-glenohumeral external rotation) exhibited during the backswing phase was 1:2.3. CONCLUSIONS The peak resultant shoulder external rotation was generated by a synchronized combination of the scapular posterior tilt and glenohumeral external rotation. A consistent pattern of three phases of the scapular posterior tilt and the glenohumeral external rotation that could be accurately modeled by three linear regressions was observed in preparation for the peak shoulder external rotation in tennis serve.

Gender differences in hip and ankle joint kinematics on knee abduction during running

Abstract The knee is the most common site of running injuries, particularly prevalent in females. The purpose of this study was to clarify gender differences in the lower extremity kinematics during running, with a specific emphasis on the relationships between the distal and proximal factors and the knee joint kinematics. Eleven female and 11 male runners participated in this study. Three-dimensional marker positions were recorded with a motion analysis system while the subjects ran along a 25 m runway at a speed of 3.5 m/s. Kinematic variables were analyzed for the stance phase of the right leg. Female runners demonstrated significantly greater peak knee abduction (P<0.05), hip adduction (P<0.01) and internal rotation (P<0.05), whereas male runners demonstrated significantly greater peak rearfoot eversion (P<0.01). The knee abduction angles were positively correlated with hip adduction angles (r=0.49, P<0.05) and negatively correlated with rearfoot eversion (r= −0.69, P<0.001). There was no significant difference in normalised step width between genders (P>0.05). Smaller rearfoot eversion and greater hip adduction related closely to the greater knee abduction as the distal and proximal factors, respectively. These relationships are thought to be the compensatory joint motions in the frontal plane, because there was no significant difference in the normalised step width between females and males. The current results suggest that if the step width is identical, the subjects with greater knee abduction had smaller rearfoot eversion to compensate for greater hip adduction, which were more apparent in females. This explains greater knee abduction found in female runners, which can be linked to a high risk of knee injury.

Twitch potentiation after voluntary contraction and neuromuscular electrical stimulation at various frequencies in human quadriceps femoris

Introduction: In this study we aimed to compare the extent of twitch potentiation (TP) after voluntary contraction and percutaneous electrical stimulation of muscles (neuromuscular electrical stimulation: NMES) with various stimulation frequencies at equivalent target levels. Methods: Isometric knee extensions of 10 s were performed at a 40% maximal voluntary contraction level by voluntary or NMES conditioning contractions at 20, 40, and 80 HZ of the quadriceps femoris muscle. Twitch responses were elicited by stimulating the femoral nerve transcutaneously at supramaximal intensity. Results: NMES at 80 HZ induced significantly less TP (128.7 ± 17.1%) than voluntary contraction (156.2 ± 23.1%), whereas no statistical difference was found in TP among voluntary and 20‐ and 40‐HZ NMES conditioning contractions (170.8 ± 21.1% and 162.7 ± 16.9% for 20‐ and 40‐HZ NMES, respectively). Conclusion: Stimulation frequency of NMES determines whether NMES can induce TP comparable to that after voluntary contraction. Muscle Nerve 45: 110–115, 2012