Neuromuscular adaptations induced by low load resistance training method with skin cooling / 体力科学

Loss of muscle strength is not only associated with loss of muscle mass, but also affected by neural factors. It is well known that facilitatory and inhibitory responses of spinal motor neurons occur with cutaneous stimulation via spinal interneurons. The purpose of this study was to examine the neural adaptations associated with low load resistance training utilizing skin cooling (SC). 10 men trained both legs and each side was randomly assigned to SC training (SC-T) and non SC training (NSC-T). Subjects performed 30 isometric ankle dorsiflexion repetitions at 35% maximum voluntary contraction (MVC) 3 times weekly for 6 weeks. The skin cooling condition was defined as when skin temperature was 25°C while repetitive resistance training was being performed. Dorsiflexor MVC significantly increased in both SC-T (n = 9) and NSC-T (n = 9) by 12.8 and 3.8%, respectively. A significant increase in root mean square of EMG (rmsEMG) was observed for 30 isometric ankle dorsiflexion repetitions in SC-T both pre- and post-training. Lower leg girths did not significantly increase post-training. Therefore, the results of this study suggest that muscle strength might increase via changes in neural activation and that SC-T may lead to greater increases in muscle strength compared with NSC-T because of improved muscle activation during resistance training with SC. Therefore, we suggest that low load resistance training with SC is an effective method to increase muscle strength.

EFFECT ON DECLINE IN HEART RATE INDUCED BY OCULAR COMPRESSION AND APNEA AFTER EXERCISE / 体力科学

<b>Object </b>: The purpose of this study was to test the response of the decline in heart rate (HR) induced by compression on the eyeball (eyeball pressure : EP) and voluntary non breath (VNB) after pedaling exercise. <b>Methods </b>: EP ; Nine male subjects performed exercise for 3 min in a supine position using a bicycle ergometer. Immediately after the exercise all subjects received EP for 10 seconds. After that, subjects undertook the same protocol without EP (CON-E). VNB ; Four male and two female subjects performed exercise for 5 minutes using a bicycle ergometer. Immediately after the exercise subjects received VNB for 7 seconds. After that subjects undertook the same protocol without VNB (CON-V). <b>Results </b>: The slope of the decline in HR recovery (HR_DS) after exercise in EP increased significantly more than that in CON-E (p<0.05). However, time constant (HR_TC) in CON-E declined faster than that in EP. Thereby, the relationship between HR_DS in EP and HR_TC in CON-E correlated (r=-0.562). The HR_DS of VNB was greater than that of EP and CON-V. However the relationship between HR_DS in VNB and HR_TC in CON-V did not correlate. <b>Conclusion </b>: We suggest that EP affects vagal nervous activity and VNB affects strength of baroreflex sensitivity. Therefore HR_DS of EP might evaluate vagal nervous activity.

EFFECT OF ECCENTRIC EXERCISE ON OXIDATIVE DNA DAMAGE IN RAT SKELETAL MUSCLES / 体力科学

Vigorous exercise induces a muscular oxidative DNA damage due to increased generation of reactive oxygen species (ROS). However, it is not fully understood how ROS induces muscular DNA damage after vigorous exercise. This study examined the relation between muscle damage and the muscular oxidative DNA damage in the gastrocnemius (GAS) and soleus (SOL) muscles of rats after eccentric exercise. All rats performed level (0 degree ; L) or downhill (—17 degrees ; DH) running on a treadmill for 1h at 20 m/min. In GAS, the 8-hydroxy-2'-deoxyguanosine (8-OHdG) content, an indicator of DNA damage, showed a 2-3 times increase from that in the control after DH running, but not after L running (P<0.05). The 8-OHdG content was positively correlated with lipid peroxide (TBARS) (r=0.61, P<0.01). Moreover, plasma creatine kinase (CK) activity was positively correlated with 8-OHdG content (r=0.68, P<0.05) and TBARS (r=0.64, P<0.05) after both DH and L running. The 8-OHdG content in SOL showed larger changes than that in GAS during the 1-week recovery period following DH running. These findings show that the exercise-induced muscular DNA damage is reflected in plasma CK activity. Consequently, it is suggested that changes in plasma CK activity can also be useful as an indicator of muscular DNA damage.

Effect of Visual input on stretch responses of ankle muscles during movements to absorb impact / 体力科学

The purpose of this study was to examine the effect of the different visual and vestibular inputs on EMG response of ankle muscles during movement to absorb impact in sliding down a slope. Thereby, our research focused on the relationship between preactivation (PA) in central program and stretch reflex induced by dorsiflexion immediately after impact. The subjects were nine healthy males. Movements were conducted using a special sliding apparatus. Conditions included sliding down a lower 15°slope with eyes open (Low) and with eyes closed (Low-Closed), and a higher 20°slope with eyes open (High) . PA prior to impact indicated the co-contraction of the medial gastrocnemius (MG) and tibialis anterior (TA) . PA levels in those muscles were significantly higher during High than during Low-Closed (p<0.05) . In contrast, PA of the coleus (Sol) was low in all test conditions. After impact, however, the stretch reflex of Sol during Low-Closed was greater than other test conditions. Because muscle stretch velocities and PA levels of Sol among all test conditions remained unchanged, these results suggest that different visual inputs could change the response of stretch reflex by modulations in reflex gain.