The purpose of this study was to investigate the effects of short-term creatine intake on muscle fatigue induced by resistance exercise in healthy adolescent men, i.e., lactic acid concentration and wrist and head tremor measured by an accelerometer. [Methods] Twelve healthy adolescent men who had no experience with creatine intake were included. The subjects were randomly assigned to the creatine group and the placebo group, followed by 5 days of creatine and placebo intake, and 5 times of 5 sets of leg press, leg extension, bench press, and arm curl exercises at 70% repetition maximum (RM). The lactic acid concentration before and after exercising, rate of perceived exertion (RPE), and accelerometer-based wrist tremor and head tremor during exercise were measured. Subsequently, after 7 days to allow for creatine washout, the same exercise treatment and measurement were performed in each group after switching drug and placebo between the groups. [Results] The level of lactic acid before and after the acute resistance exercise trial was significantly lower in the creatine group than in the placebo group (P <0.05). The mean RPE during the resistance exercise was significantly lower in the creatine group than in the placebo group (P <0.05). There was no difference between the two groups in the mean wrist tremor during resistance exercise, but the mean head tremor values were significantly lower in the creatine group than in the placebo group in the arm curl, the last event of the exercise trials (P <0.05). [Conclusion] Short-term creatine intake reduces the blood fatigue factor increased by resistance exercise, and is thought to suppress fatigue, especially in the latter half of resistance exercise. Therefore, these findings indicate that short-term creatine intake can have an improved effect on anaerobic exercise performance.

[Purpose] To date, there have been no studies on the response of wrist tremor to increased muscle activity during exercise. This study aimed to evaluate the wrist tremor response with increasing muscle activity during bench press exercise. [Methods] Triceps muscle activity and wrist tremor response were measured by electromyography and an accelerometer, respectively, during bench press exercise in 11 healthy men without weight-training experience. Subjects performed bench press at 30% repetition maximum (RM), and the rating of perceived exertion (RPE) and lactate concentration were measured before and after exercise. One week later, an equivalent number of bench presses at 30% RM was performed without weight load as a control trial (CT). [Results] RPEs and lactate concentrations significantly increased after resistance exercise (30% RM) from 7.4 to 14.3 and 1.7 to 4.9, respectively (P<.01), but no such difference was observed in the CT. Muscle activity linearly increased during the 30% RM exercise, and wrist tremors were shown to linearly decrease. A strong negative correlation was observed between the two variables (r=−0.88, P<.001). [Conclusion] We found that wrist tremors during resistance exercise, as measured using an accelerometer, can be used to predict muscle activity.

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[Purpose] This study aimed to compare the physiological tremor, grip strength, and cognitive function of sedentary and physically active older adults.[Methods] Twenty-four older adults aged ≥65 years participated in this study and were divided into the sedentary (76.5±4.4 years, n=12) and physically active (73.5±3.3 years, n=12) groups. Each group completed the Mini-Mental State Examination (MMSE) for cognitive function assessment. Physiological tremor was measured using an accelerometer for both hands at rest and the left/right hand with a 1,000 g dumbbell on the palm in neutral positions and the elbow flexed at 90°. Physical fitness was measured by grip strength and completion of the Short Physical Performance Battery (SPPB) and the 6-min walk test.[Results] The physically active group showed a significantly lower level of physiological tremor in both hands at rest and the left/right hand with a 1,000 g dumbbell on the palm (P<0.05) than that in the sedentary group. For cognitive function, the physically active group showed significantly higher scores than those in the sedentary group (P<0.001). No significant correlation was found between cognitive function and left/right grip strength (left: r = 0.117, P = 0.585; right: r = 0.230, P = 0.279), physiological tremor in both hands at rest (left: r = -0.524, P < 0.001; right: r = -0.508, P < 0.05), and the left/right hand with a 1,000 g dumbbell on the palm (left: r = -0.505, P < 0.05; right: r = -0.458, P < 0.05).[Conclusion] Physiological tremor of the hands has the potential to be a useful predictor of cognitive function in older adults.

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