EFFECTS OF DIATHERMIC-WARMING OF WORKING MUSCLES ON??VO2-KINETICS DURING HEAVY EXERCISE

Abstract

1068 Prior heavy exercise which induces a La acidosis (i.e., supra-LT exercise) could speed the ˙VO2-kinetics of subsequent heavy exercise using same muscles, and this could be due to improved muscle perfusion via acidosis-induced vasodilating effects ( J.Appl.Physiol., 80:99-107, 1996). However, ˙VO2-kinetics are not faster if supra-LT arm cranking is substituted for leg cycling as the 1st bout for inducing La acidemia (presented in the Meeting of Br.Physiol.Soc. in January, 1998). This suggests that another mechanism(s), other than La acidemia per se, is responsible for the faster ˙VO2 response to subsequent heavy exercise. Therefore, we investigated the possibility of muscle warming influencing ˙VO2-kinetics during a following bout of leg heavy exercise. Eight healthy subjects (aged 21-42 years) volunteered to participate in this study. The control condition consisted of two consecutive 6-min leg cycling exercise bouts (the work rate: Δ50% between LT and˙VO2max) separated by 6-min baseline at 20 W (L1-ex to L2-ex). In the experimental condition, diathermic warming to the front thigh was substituted for 1st bout leg exercise. This elevated muscle temperature prior to determining the subsequent ˙VO2-kinetics of leg heavy exercise(H2-ex). In the control condition, ˙VO2-kinetics for the 2nd supra-LT bout were significantly faster than the 1st bout [the mean±S.D. of the “effective” τ by mono-exponential fitting, L1-ex: 53.8±11.6 s, L2-ex: 38.7±7.9 s]. However, the elevated muscle temperature induced by diathermia did not alter the˙VO2-kinetics of subsequent supra-LT leg exercise [τ in H2-ex: 52.3±7.7 s]. It was concluded that the speeding of the˙VO2-kinetics during supra-LT exercise by prior heavy exercise was not be due to the increased muscle temperature.