RESUMO
Aerobic dance (AD) is a form of fitness exercise whose program is constructed by a combination of various joint movements. Therefore the exercise is expected to give enough stimulus to not only the cardiorespiratory but also the musculoskeletal system. The purpose of this study was to evaluate the activity level of the leg muscles among the major 22 AD leg movements, or steps (13 low-impact steps and high-impact steps), by electromyography (EMG) analysis. The subjects were two trained AD instructors, who were asked to perform individual steps at a pitch of 144 bpm. EMG data were recorded from the iliopsoas, gluteus maximus, vastus lateralis, biceps femoris, tibialis anterior, and gastrocnemius muscles on the right side by means of surface electrodes. The half-wave of the raw EMG was rectified and integrated over periods of 20 s during the exercise. From the raw EMG data it was observed that the pattern and amplitude of the electrical discharge of each muscle varied in response to the difference in step motion. The integrated EMGs of the iliopsoas, biceps femoris, and gastrocnemius tented to show higher values for high-impact steps in comparison with low-impact steps, but that of the tibialis anterior showed a contrary trend. The mean value and stan-dard deviation of iEMG of each muscle for the 22 steps was calculated for the same subjects, and the muscle activity level was classified into 5 degrees. Making use of this evaluation table, it may be possible to construct an AD program that can activate the leg muscles impartially.
RESUMO
To investigate the relationship between maximal aerobic power (VO<SUB>2</SUB>max) and fatigu-abililty during repeated isokinetic contractions, 39 male speed skaters (mean 20.8 years) served as subjects. They were divided into two groups according to their VO<SUB>2</SUB>max levels ; high VO<SUB>2</SUB>max group (HI, n=19) and low VO<SUB>2</SUB>max group (LO, n=20) . VO<SUB>2</SUB>max was measured in all subjects during incremental exercise on a bicycle ergometer and body composition was determined by densitometry. Cross-sectional area (CSA) of the leg extensor muscles was evaluated using ultrasonic method. Fatiguability was assessed during the fatigue test consisting of 50 repeated isokinetic knee-extensions at an angular velocity of 180 deg⋅sec<SUP>-1</SUP>. Remark-able findings include :<BR>1. There were no significant differences in body composition and thigh composition between the two groups except for high subcutaneous fat in group LO.<BR>2. There were significant differences in VO<SUB>2</SUB>max between group HI (3.93<I>l</I>⋅min<SUP>-1</SUP>, 67.3 m<I>l</I>⋅kg LBM<SUP>-1</SUP>⋅min<SUP>-1</SUP>) and group LO (3.59<I>l</I>⋅min<SUP>-1</SUP>, 59.9 m<I>l</I>⋅kg LBM<SUP>-1</SUP>⋅min<SUP>-1</SUP>) .<BR>3. In the fatigue test, the average initial values did not differ, however, the average final values were higher in group HI. Also, a significant difference was observed in per unit CSA between the two groups.<BR>4. Higher peak forces (kg) in group HI were observed after the initial 30 dymanic contractions per unit CSA and % of peak values (% peak force) .<BR>5. A close relationship was demonstrated between VO<SUB>2</SUB>max per LBM and the fatigue index, i. e., the mean decline in peak force with 50 contractions (r=-0.37, p<0.05) .<BR>Based on the present findings it is suggested that maximal aerobic power (VO<SUB>2</SUB>max) influences the rate of fatigue development even during short-term maximal isokinetic contractions, and that there may be some physiological cross-linkages between cardiopulmonary regulation and the metabolic properties of skeletal muscles. This finding is also in conformity with earlier results indicating the importance of oxygen delivery as a limiting factor for muscle performance.