Causes of Different Force-Velocity Relationships in Sprint Running Depending on Horizontal Loads and Profiling Methods.

Purpose: We aimed to clarify how the horizontal force-velocity (Fvh) relationship during over-ground sprint running differs with horizontal resistance loads and profiling methods (multiple- and single-trial methods).

Methods: Twelve males performed sprint running (one unresisted and five resisted) using a motorized loading device. During the trials, the ground reaction forces at every step were obtained using a 50 m force plate system.

Validity of spatiotemporal and ground reaction force estimates during resisted sprinting with a motorized loading device.

We aimed to examine the validity of estimating spatiotemporal and ground reaction force (GRF) parameters during resisted sprinting using a robotic loading device (1080 Sprint). Twelve male athletes (age: 20.9 ± 2.

Measuring Muscle Activity in Sprinters Using T2-Weighted Magnetic Resonance Imaging.

Purpose: This study aimed to investigate the level of muscle activity during sprint running using T2-weighted magnetic resonance imaging.

Methods: Fourteen male sprinters (age 21.2 [4.

Muscle stiffness of the rectus femoris and vastus lateralis in children with Osgood-Schlatter disease.

Background: The relevance of the mechanical properties of muscles in relation to Osgood-Schlatter disease (OSD) remains unclear. The present study aimed to examine rectus femoris (RF) and vastus lateralis (VL) muscle stiffness in children with OSD.

Methods: A total of 28 legs affected by OSD and 26 legs without OSD were assessed.

Associations Between Individual Lower-Limb Muscle Volumes and 100-m Sprint Time in Male Sprinters.

Purpose: To elucidate the relationship between the muscularity of individual lower-limb muscles and 100-m-race time (t) in young-adult male sprinters.

Methods: Thirty-one young-adult male sprinters took part in this study (age 19.9 ± 1.

Validity of muscle thickness-based prediction equation for quadriceps femoris volume in middle-aged and older men and women.

Background: This study examined the validity of muscle thickness (MT)-based prediction equation for the muscle volume of the quadriceps femoris (QFMV) by evaluating the applicability of a prediction equation previously derived from young men and by developing a new prediction equation in middle-aged and older individuals.

Methods: The MT at the midpoint of the thigh anterior and QFMV were determined using ultrasonography and magnetic resonance imaging in 30 men and 30 women aged 51 to 77 years. First, we examined the validity of the MT-based prediction equation previously developed for young men to estimate the QFMV of middle-aged and older individuals.

Influence of muscle hypertrophy on the moment arm of the triceps brachii muscle.

Although the moment arm of the triceps brachii muscle has been shown to be associated with the muscle's anatomical cross-sectional area, whether training-induced muscle hypertrophy alters the moment arm of the muscle remains unexplored. Therefore, the current study aimed to examine this. Eleven men underwent a 12-week resistance training program for the triceps brachii muscle.

Difference in the recruitment of hip and knee muscles between back squat and plyometric squat jump.

Athletes who aim to improve both muscular endurance and power often perform exercises that involve similar joint actions under different lifting conditions, such as changes in the load or speed, which are implemented at different times during a periodized exercise program or simultaneously. The prescribed exercises are considered to recruit the same muscles even if the lifting conditions differ to each other. The present study aimed to clarify this by examining whether the recruitment of individual hip and knee muscles during the squat exercise differs between lifting conditions adopted for muscular endurance and power training regimens.

Intensity-level assessment of lower body plyometric exercises based on mechanical output of lower limb joints.

The present study aimed to quantify the intensity of lower extremity plyometric exercises by determining joint mechanical output. Ten men (age, 27.3 ± 4.

Association between regional differences in muscle activation in one session of resistance exercise and in muscle hypertrophy after resistance training.

The purpose of this study was to examine if the regional difference in muscle hypertrophy after chronic resistance training is associated with muscle activation after one session of resistance exercise. Twelve men performed one session of resistance exercise of elbow extensors. Before and immediately after the exercise, transverse relaxation time (T2)-weighted magnetic resonance (MR) images of upper arm were recorded to evaluate the muscle activation along its length.

Effect of muscle contraction levels on the force-length relationship of the human Achilles tendon during lengthening of the triceps surae muscle-tendon unit.

Findings from animal experiments are sometimes contradictory to the idea that the tendon structure is a simple elastic spring in series with muscle fibers, and suggest influence of muscle contraction on the tendon mechanical properties. The purpose of the present study was to investigate the influence of muscle contraction levels on the force-length relationship of the human Achilles tendon during lengthening of the triceps surae muscle-tendon unit. For seven subjects, ankle dorsiflexion was performed without (passive condition) and with contraction of plantar flexor muscles (eccentric conditions, at 3 contraction levels) on an isokinetic dynamometer.

Effect of countermovement on elbow joint extension power-load characteristics.

The aim of the present study was to examine elbow joint extension power-load characteristics with and without a countermovement. Eight male participants performed maximal elbow extensions with and without a countermovement against different loads (0, 2.5, 5.

Influence of muscle anatomical cross-sectional area on the moment arm length of the triceps brachii muscle at the elbow joint.

The purpose of this study was to test the hypothesis that the musculotendon moment arm length is affected by the muscle anatomical cross-sectional area. The moment arm length of the triceps brachii (TB) muscle at 30°, 50°, 70°, 90°, 110° elbow flexion positions was measured in sagittal magnetic resonance images (MRI) of 18 subjects as the perpendicular distance between the center of the pulley of the humerus to the line through the center of the TB tendon. The moment arm increased as the elbow flexion angle decreased, from 1.

Fatigue-induced changes in synergistic muscle force do not match tendon elongation.

This study aimed to investigate whether fatigue-induced changes in synergistic muscle forces match their tendon elongation. The medial gastrocnemius muscle (MG) was fatigued by repeated electrical stimulation (1 min x 5 times: interval 30 s, intensity: 20-30% of maximal voluntary plantar flexion torque) applied at the muscle belly under a partial occlusion of blood vessels. Before and after the MG fatigue task, ramp isometric contractions were performed voluntarily, during which tendon elongations were determined by ultrasonography, along with recordings of the surface EMG activities of MG, the soleus (SOL) and the lateral gastrocnemius (LG) muscles.

Joint angle dependence of intermuscle difference in postactivation potentiation.

The purpose of this study was to examine the effect of ankle joint angle on the intermuscle difference in postactivation potentiation (PAP) between the medial gastrocnemius (MG) and soleus (SOL) muscles. At the neutral position of joint angle, dorsiflexion of 20 degrees , and plantarflexion of 20 degrees , twitch responses were evoked by stimulating the posterior tibial nerve with supramaximal intensity before and after a 10-s maximal voluntary plantarflexion at each joint angle. Mechanical properties of the MG and SOL muscles were assessed simultaneously and separately by using mechanomyography (MMG), and the extent of potentiation of each muscle was evaluated by peak-to-peak amplitude of the MMG signal.

Fatigue-related changes in fascicle-tendon geometry over repeated contractions: difference between synergist muscles.

Fatigue-induced changes in force production of synergist muscles were evaluated through observation of fascicle-tendon geometry and electromyography (EMG). Seven subjects performed 60 maximal isometric plantar flexions intermittently. No statistically significant intermuscle difference was observed in the decrease of mean EMG amplitudes or mean power frequency for the medial gastrocnemius (MG) and soleus (SOL) muscles.