The field study about the effects of artificial CO2-rich cool-water immersion after outdoor sports activity in a hot environment.

Background/objective: In our previous laboratory experiment (room temperature of 25 °C), CO2-rich cool-water immersion (CCWI) suppressed subjects' core body temperature even during repeated exercise. It is unclear whether the suppression of body temperature elevation would also continue after CCWI in a hot outdoor environment. Herein we investigated the thermal effects of CCWI after regular exercise training in heat on subjects' core temperature (Tcore), three skin temperatures (Tskin), heart rate (HR), and the rate of perceived ice (RPI). Methods: Thirty-six subjects (25 males, 11 females) were randomly allocated into three groups (CCWI, CWI, and control). After training at their competitive clubs, each subject was immersed up to the chest in CCWI or CWI at 20 °C for 20 min, followed by a 60-min recovery period. Tcore, Tskin, HR, and RPI were measured at the initial rest, the end of immersion, and every 10 min during the recovery period. Results: Compared to the control, the CCWI subjects' Tcore was significantly lower at 50-60 min after the end of immersion (p < 0.05). Tskin at abdominal and lower-leg regions during the recovery period was maintained at significantly lower values in the CWI and CCWI groups versus control (p < 0.05). The CCWI subjects maintained lower Tskin for a longer time than the CWI subjects. Conclusions: These findings indicate that CCWI suppresses the rise in body temperatures more than CWI, even in a hot environment, suggesting that CCWI may be a more effective countermeasure against increasing body temperature in a hot outdoor environment.

Agonist-antagonist muscle activation during drop jumps.

Pre-programmed and stretch-induced muscle activities of agonist muscles can play important roles during stretch-shortening cycle exercises. It is still not clear how the antagonist muscles function when the drop and rebound intensities are varied during drop jump (DJ) exercises. The purpose of the present study was to examine the regulation of agonist-antagonist muscle activation during DJ with different drop and rebound heights. The subjects performed DJs with two drop heights (0.2 and 0.4 m) and three different efforts (maximal rebound height, 50% effort of maximal rebound height and landing without rebound). Ankle and knee joint angles, and vertical ground reaction force together with an electromyogram of the lower leg muscles (medial gastrocnemius [MG], soleus [SOL] and tibialis anterior [TA]) were measured simultaneously during DJ. Our results clearly showed that the pre-activation of the antagonist TA was increased with increasing rebound height. Our results further showed that the coactivations of agonist and antagonist muscles during the post-impact 30-ms phase were increased with increasing rebound height. These results suggested that not only the pre-programmed agonist MG muscle activation, but also the pre-programmed antagonist TA activation and the coactivation of the post-impact 30-ms phase may play important roles in the control of rebound height.

Relationship between peak VO2 and subcutaneous fat thickness of the thigh measured by ultrasonography.

BACKGROUND: Measured physical activity and percent body fat obtained by bioelectrical impedance analysis have been used as indicators of cardiorespiratory fitness in middle-aged women and children. However, the relationship between subcutaneous fat thickness in various regions of the thigh determined by ultrasonography and cardiorespiratory fitness has not been previously reported. METHODS: We measured subcutaneous fat thickness in the frontal, lateral, and medial regions of both thighs using ultrasonography, and also determined peak VO2 and percent body fat in 13 healthy and generally well female college students. RESULTS: There were significant negative correlations found between peak VO2 and the 3 frontal portions of the thigh, as well as the vastus lateralis (both sides), while correlations were not seen with the right and left medial regions 15 cm above the medial epicondyle. CONCLUSIONS: Our results suggest that increases in peak VO2 are reflected by decreases in subcutaneous fat thickness in the frontal and lateral regions of the thigh, but not in decreases in that in both sides of the medial region of the thigh. In addition, subcutaneous fat thickness may indicate partial or segmental activation of the frontal and lateral regions of the legs, such as that obtained by cycling. We concluded that measurement of subcutaneous fat thickness in the region above the muscle mass of the thigh such as the rectus femoris or lateral vastus using ultrasonography may reasonably represent physical activity. Further study is needed to be done with larger groups of subjects and to evaluate the effects of training on activation of regions of the thigh.