Muscle strength decreases with age and resistance training is an important method for preventing a decrease in muscle strength, known as sarcopenia. It has been reported that the contribution of neural adaptation and muscle hypertrophy after training is different between younger and older adults, and neural adaptation plays a greater role in the increase of muscle strength in older adults. Fall prevention is another important reason why understanding muscle characteristics, including neural factors, is necessary when considering training methods for older adults. Instantaneous muscle activity, which can be evaluated by the rate of force development (RFD), is a very important factor to consider in older adults, especially as RFD decreases with age. Although high intensity training improves RFD in older adults, it is inappropriate for this age group due to the stress it puts on the cardiorespiratory system. Therefore, a low intensity training method which has a positive effect on neural adaptation is required for older adults. It has been reported that cutaneous input, such as skin cooling, during training is an effective method for evoking neural adaptation in older adults. Some reports have suggested that resistance training with skin cooling improves muscle strength in older adults. Moreover, skin cooling increases RFD during muscle contraction in younger adults. Although further investigation about the effects of training with skin cooling is necessary to establish effective training methods, training with skin cooling has the potential for positive adaptation of neural factors in older adults.
It’s reported that body fat percentage increases with increasing weight class, with an especially rapid increase in ≥ 90kg classes. The purpose of this study was to compare changes of core temperature and skin temperatures before and after a Judo match between men < 90 kg and ≥ 90 kg. This study included 13 men who were divided into 2 groups: “< 90 kg” and “≥ 90 kg”. Body fat percentage was measured before the match, while heart rate, core temperature and skin temperature (Thigh, Tsurite, and Hikite temperatures) were measured before and 1, 10, and 20 min after the match. Body fat percentage in ≥ 90 kg was significantly higher than < 90 kg (p < 0.01). Heart rate and core temperature showed no significant difference. Thigh, Tsurite, and Hikite temperatures measured 10 min after the match were significantly higher in ≧90 kg than < 90 kg (p < 0.05). There was significant correlation between body fat percentage and rate of change of Thigh (rs = 0.69, p < 0.01), Tsurite (rs = 0.41, p < 0.05), and Hikite (rs = 0.49, p < 0.01) temperatures between 1 and 10 min after the match. The results of this study demonstrate that male Judo athletes with higher body fat percentage continue to have high skin temperatures after the match.
The purpose of this study was to examine changes in muscle activation with skin cooling (SC) to determine the optimal levels of force at which skin cooling has an effect on the recruitment of fast twitch muscle fiber. Subjects performed an isometric dorsiflexion with SC and without SC at 10%, 20%, 30%, 40%, 50%, 60%, and 70% of maximal voluntary contraction, in random order. Surface electromyography (EMG) were obtained from the tibialis anterior muscle. Skin temperature was maintained at 25℃ using a gel-cooling pad. Muscle temperature did not change with skin cooling. The root mean square of the EMG (rmsEMG) with SC was significantly greater than without SC in contractions from 10% to 50% MVC. Skin cooling displayed significantly lower mean power frequency (MPF) values than without SC at the seven different force levels. Changes in rmsEMG and MPF may indicate a reduction in the threshold of high threshold motor units (HT-MUs), along with inhibition of low threshold motor units (LT-MUs) and substitution of LT-MUs with HT-MUs. We propose that skin cooling can be used as a form rehabilitative training, optimally targeting the recruitment of fast twitch muscle fiber.
Postural control pivoting at the ankle has been suggested to decline in the elderly. Such declination is supposed to be also recognized in postural control during forward and backward leaning. However, the positive evidence has not been found. In this study, we investigated the postural movement patterns while forward and backward leaning for the elderly. Subjects were 16 healthy young adults and 20 elderly adults. They maintained extreme forward and backward leaning (EFL and EBL) posture from quiet standing posture. The center of pressure in the anteroposterior direction (CoPap) and the movement angle of ankle, knee and hip were measured. Mean CoPap positions in EFL and EBL posture showed no significant differences between the young and elderly. In the young, all the movement angle of leg joints changed toward the same direction as leaning posture. On the other hand, in the elderly, the movement angle of ankle did not change in EFL posture and significantly moved forward in EBL posture. The movement angles of knee and hip were significantly larger in the elderly than the young. These results indicate that in the young, EFL and EBL posture could be controlled with pivoting at the ankle, while in the elderly, this controllability would be deteriorated and the target of postural control would shift to the knee and hip.
We have developed analyses of the brain activity in postural control under the dynamic condition, using various sensory evoked potentials and event-related potentials. In this paper, we described the outline of representative sensory evoked potentials and event-related potentials and the summary of our previous studies measuring these brain potentials. In addition, we summarized the recording methods of the brain potentials and presented the representative flowchart of the brain potential measurement.