Mitsumasa Miyashita

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 %, t7% and 34% of the total calf muscle work in the squat jump, the counter movement jump, and hopping, respectively.

Determination and validity of critical velocity as an index of swimming performance in the competitive swimmer

SummaryThe purpose of this investigation was to test whether the concept of critical power used in previous studies could be applied to the field of competitive swimming as critical swimming velocity (νcrit). The νcrit, defined as the swimming velocity over a very long period of time without exhaustion, was expressed as the slope of a straight line between swimming distance (dlim) at each speed (with six predetermined speeds) and the duration (tlim). Nine trained college swimmers underwent tests in a swimming flume to measure νcrit at those velocities until the onset of fatigue. A regression analysis ofdlim on trim calculated for each swimmer showed linear relationships (r2>0.998,P<0.01), and the slope coefficient signifying νcrit ranged from 1.062 to 1.262 m · s−1 with a mean of 1.166 (SD 0.052) m · s−1. Maximal oxygen consumption (

Specificity of velocity in strength training

\dot VO_{2\max }

Differences in activation patterns in elbow flexor muscles during isometric, concentric and eccentric contractions.

), oxygen consumption (

Muscle fiber conduction velocity related to stimulation rate

\dot VO_2

The estimation of conduction velocity in human skeletal muscle in situ with surface electrodes

) at anaerobic threshold, and the swimming also velocity at the onset of blood lactate accumulation (νOBLA) were also determined during the incremental swimming test. The νcrit showed significant positive correlations with