Neuromuscular modulation was observed with the application of menthol gel at low loads in the present study. These findings could lead to a new method of muscular training that targets the recruitment of fast type muscle safe for older adults.
Modulation of muscle activation in superficial and deeper regions may be induced by tactile stimulation. The purpose of this study was to examine changes in muscle activation with skin friction. Subjects performed an isometric elbow flexion at 30% maximal voluntary cotraction (MVC) with skin friction at different frequencies (0.5-2.7 Hz). Surface electromyography (S-EMG) and intramuscular EMG were obtained from the elbow flexor muscles (BBS: short head of biceps brachii, BBL: long head of biceps brachii, BRA: brachialis). S-EMG activity decreased at a higher frequency of 2.7 Hz and increased linearly with an increase in skin friction frequency (0.5-2.7 Hz) in BBS. A decrease in high-threshold motor unit (HT-MU) firing rate in superficial regions and an increase in low-threshold motor unit (LT-MU) firing rate in deeper regions were observed with skin friction (2.7 Hz) in BBS. The actions of inhibitory interneurons may be influenced by cutaneous afferent input with skin friction. Muscle activation of BBS depended on the intensity of the stimulus. Skin friction over BBS results in an inhibitory response in superficial regions of BBS, most likely due to the increase in firing rate of low-threshold cutaneous mechanoreceptors.
Abstract. [Purpose] To examine electromyographic (EMG) activity change during dynamic contraction of the quadriceps with skin cold stimulation (SCS) over the vastus lateralis (VL) and L4 dermatome area on the medial side of the lower leg. [Subjects and Methods] Seventeen healthy male volunteers participated. Dynamic knee extension was performed at 15% maximum voluntary contraction (MVC). SCS is a method used to cool the skin to 25 °C using a gel-cooling pad. The SCS method has no effect on the muscle below the cooled skin. Subjects performed dynamic knee extension under 4 randomly selected conditions: (1) SCS of skin over the VL (SCS VL ), (2)without SCS of skin over the VL (non-SCS VL ), (3) SCS of L4 dermatome area on the medial side of the lower leg (SCS L4 ), and (4) without SCS of L4 dermatome area on the medial side of the lower leg (non-SCS L4 ). Surface EMG from the rectus femoris (RF), VL, and vastus medialis (VM) were recorded using miniature electrodes.[Results] The root mean square of the EMG (rmsEMG) of the VL with SCS was significantly greater than activation without SCS, but was decreased by SCS L4 . However, the activity of RF and VM did not change in any condition.[Conclusion] Our results suggest that the influence of cutaneous input can demonstrably modulate muscle activation.
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.
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