Kazutaka Fujishima

Muscle activity and heart rate response during backward walking in water and on dry land

AbstractThe primary purpose of this study was to examine whether walking backward in water and walking backward on dry land elicit different electromyographic (EMG) activities in lower-extremity and trunk muscles. Surface EMG was used to evaluate muscle activities while six healthy subjects walked backward in water (with and without a water current, Water + Cur and Water − Cur, respectively) immersed to the level of the xiphoid process, and while they walked backward on dry land (DL). The trials in water utilized the Flowmill which consists of a treadmill at the base of a water flume. Integrated EMG analysis allowed the quantification of muscle activities. The measurement of maximal voluntary contraction (MVC) of each muscle was made prior to the gait analysis, and all data were expressed as the mean (SD). The %MVCs from the muscles tested while walking backward in water (both with and without a current) were all significantly lower than those obtained while walking backward on dry land ( P<0.05), with the exception of the paraspinal muscles. In the case of the paraspinal muscles, the %MVC while walking backward with a water current was significantly greater than when walking backward on dry land [Water + Cur 19.4 (6.8)%MVC vs. DL 13.1 (1.4)%MVC; P<0.05], or walking backward without a water current [vs. Water − Cur 13.3 (1.8)%MVC; P<0.05]. Furthermore, when walking backward in water, the %MVCs from the muscles investigated were significantly greater in the presence of a water current than without ( P<0.05). In conclusion, walking backward in water with a current elicits the greatest muscle activation of the paraspinal muscles. These data may help in the development of water-based exercise programs.

Human thermoregulatory responses during prolonged walking in water at 25, 30 and 35°C

Abstract Eight healthy and physically well-trained male students exercised on a treadmill for 60 min while being immersed in water to the middle of the chest in a laboratory flowmill. The water velocity was adjusted so that the intensity of exercise correspond to 50% maximal oxygen uptake of each subject, and experiments were performed once at each of three water temperatures: 25, 30, 35°C, following a 30-min control period in air at 25°C, and on a treadmill in air at an ambient temperature of 25°C. Thermal states during rest and exercise were determined by measuring rectal and skin temperatures at various points, and mean skin temperatures were calculated. The intensity of exercise was monitored by measuring oxygen consumption, and heart rate was monitored as an indicator for cardiovascular function. At each water temperature, identical oxygen consumption levels were attained during exercise, indicating that no extra heat was produced by shivering at the lowest water temperature. The slight rise in rectal temperature during exercise was not influenced by the water temperature. The temperatures of skin exposed to air rose slightly during exercise at 25°C and 30°C water temperature and markedly at 35°C. The loss of body mass increased with water temperature indicating that both skin blood flow and sweating during exercise increased with the rise in water temperature. The rise in body temperature provided the thermoregulatory drive for the loss of the heat generated during exercise. Heart rate increased most during exercise in water at 35°C, most likely due to enhanced requirements for skin blood flow. Although such requirements were certainly smallest at 25°C water temperature, heart rate at this temperature was slightly higher than at 30°C suggesting reflex activation of sympathetic control by cold signals from the skin. There was a significantly greater increase in mean skin and rectal temperatures in subjects exercising on the treadmill in air, compared to those exercising in water at 25°C.