The purpose of this study was to examine the effect of hopping tempo on the stretch reflex of the soleus muscle at the landing phase during continuous hopping. The M 1 and M 2 components of stretch reflex of the soleus muscle and angular velocity of the ankle joint were recorded at the landing phase during hopping under four hopping tempos with frequencies of 1.0, 1.5, 2.0, and 2.5 Hz. The electromyogram (EMG) activities in the soleus muscle during the landing and the jumping phases were separated under 1.0, 1.5 and 2.0 Hz conditions, but EMG's for both phases were overlapped under 2.5 Hz condition. Furthermore, at 1.0 and 1.5 Hz, a non-active EMG phase was observed between the landing and the jumping phases ; but this non-active phase disappeared at 2.0 Hz. The M 1 and M 2 components at 2.0 Hz showed significantly (p<0.01) larger values than those at 1.0 and 1.5 Hz. However, there was no significant difference observed between the components at 1.0 and 1.5 Hz. The M 2 component showed a significantly (p <0.01) smaller value than the M 1 component at 1.0 and 1.5 Hz ; but there was no significant difference at 2.0 Hz. The angular velocity of the ankle joint showed no significant difference under any of the conditions. These findings suggest that stretch reflex at landing during hopping may be inhibited at the motion pattern of the inactive phase between the landing and the jumping phases in EMG's. In addition, the stretch reflex is not only related to mechanical muscle stretching, but is also under the influence of the superior nerve center.

The purpose of this study was to examine the effect of physical inactivity, produced by prolonged bed rest, on the excitability of the spinal motor neuron pool in humans, using the activity of soleus H-reflex.
Eight healthy male subjects underwent continuous bed rest with 6 degree head-down tilt for 20 days (BR group) . Ten different healthy male subjects maintained their usual daily life during the observation period for 20 days (control group) . Recruitment curves of H-reflex and M-wave were obtained from every subject. H slope/M slope (H slp/M sip) which shows the excitability of spinal motor neurons was calculated by using data in the recruitment curve.
The H sip/M sip in the BR group significantly increased after BR, compared to the pre-BR values (p<0.05) . In the control group, however, there were no significant differences in the H slp/M sip between the pre and the post-observation values. At the baseline, the H slp/M sip showed no significant differences between the BR group and the control group. After the BR, the H slp/M sip in the BR group significantly increased compared to the control group after the observation period (p<0.05) .
This study suggests that the excitability of the monosynaptic spinal motor neuron pool is facilitated by physical inactivity during BR.

The purpose of this cross-sectional study is to investigate the difference in physical activity among elderly living in different areas in Japan (“Bunkyo Ward in Tokyo” (Bunkyo) and “Fuchu City in Tokyo” (Fuchu) as urban areas, and “Oyama Town in Shizuoka” (Oyama) as a non-urban area). Participants were 1859 community-dwelling residents aged 65-74 years, randomly selected from the residential registry (response rate: 68.9%). A mail survey using self-administered questionnaires was conducted. Multivariate logistic regression analyses were used to calculate the adjusted odds ratios (ORs) and 95% confidence intervals (95% CI) of various types of physical activity (eg, walking (Walking), going out (Going-out), bicycling (Bicycling), exercise habits (Exercise)), according to residential areas (reference category: Fuchu), stratified by gender, adjusting for socio-demographic variables. There was a significant difference in Going-out (ORs = 0.61 (95% CI: 0.44-0.86) for men, 0.48 (0.33-0.69) for women)), and Bicycling (0.04 (0.03-0.07) for men, 0.04 (0.02-0.07) for women) in Oyama compared to Fuchu. Furthermore, for women, there was a significant difference in Walking (0.56 (0.38-0.81)) and Exercise (0.59 (0.41-0.85)) in Oyama compared to Fuchu. There was a significant difference in Bicycling and Going-out for men in Bunkyo compared to Fuchu, but there was not a significant difference in other items. Low physical activity levels were observed in the elderly in the non-urban area compared to urban areas. The association was stronger in women. Regional difference might need to be taken into account for an effective physical activity intervention.