Menthol-induced cutaneous stimulation combined with self-paced walking training improves knee extension performance in untrained older healthy females.

[Purpose] The present study aimed to investigate whether self-paced walking training utilizing the facilitating effect of skin cooling with menthol gel application was effective in untrained older healthy females. [Participants and Methods] Forty-two untrained healthy older females (aged 60-69 years) were divided into the following three groups: (i) Walking training with menthol group: GM, (ii) Walking training group: GW, and (iii) Control group: GC. The participants in GM and GW performed self-paced walking for 30 minutes a day, 2 times a week, for 6 weeks. Menthol gel was applied to the front of the thigh of the participants in GM. Maximal voluntary contraction and rate of force development were measured pre- and post-training and walking speed was measured during the training. The number of steps taken and walking speed in daily activity were measured and the average of these parameters per day were calculated. [Results] The main findings were [1] knee extension muscle strength increased in GM and GW, and [2] rate of force development only improved in GM. [Conclusion] These results suggest that walking training utilizing the facilitating effect of skin cooling enhances muscle function in untrained older healthy females and that the present skin cooling method with menthol gel application may be recommended as a training strategy.

The effects of skin cold stimulation on quadriceps muscle activity during walking in older adults.

Purpose: Given that walking speed declines with ageing and decreasing walking speed restricts activities of daily living (ADL), it is important for the old to maintain walking speed in order to prevent affecting ADL. Although skin cold stimulation (SCS) facilitates instantaneous muscle activity, which occurs during walking, the effects of SCS on muscle activity during walking remain unclear. Thus, the present study aimed to investigate the effect of SCS during walking in older adults.Methods: Seventeen community-dwelling healthy older adults (73 ± 6 years old) participated in this study. Walking speed at a comfortable pace and the electromyographic (EMG) activity of the vastus lateralis (VL) and biceps femoris (BF) were measured. SCS, which maintains the skin temperature at 25 °C, was applied to the front of the thigh during the procedures. Walking speed, root mean square EMG (rmsEMG) and mean power frequency (MPF) were compared under SCS and control conditions.Results: SCS significantly increased the walking speed (p < 0.01) and the rmsEMG of the vastus lateralis (p = 0.032). No change in the rmsEMG of the BF was observed, and SCS had no effect on MPF of both the VL and BF. Furthermore, a significant relationship was observed between these changes (r = 0.619, p = 0.042).Conclusion: SCS increased the EMG activity of the VL while increasing walking speed. Our results suggest that SCS is an effective strategy that can be included in daily life in order to improve walking ability of older adults.

Effect of stimulation of cold receptors with menthol on EMG activity of quadriceps muscle during low load contraction.

PURPOSE: Facilitatory and inhibitory responses of spinal motor neurons are influenced by somatosensory input from the skin. The purpose of this study, employing electromyography, was to examine the neuromuscular changes that occur with menthol applied to the skin over the quadriceps muscle. METHODS: Forty-two healthy volunteers performed isometric knee extensions at 35% maximum voluntary contraction (MVC) in three groups (Adult Placebo, Adult Menthol, Older Adult Menthol). Stimulation used was application of 5% menthol gel to the skin. Surface electromyography (sEMG) from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) was recorded using miniature pair electrodes. RESULTS: Root mean square electromyography (rmsEMG) in VL and VM significantly increased with menthol stimulation both in Adult and Older Adult, but no significant difference was observed between Adult Menthol and Older Adult Menthol. There was a significant decrease in mean power frequency (MPF) in VM with menthol stimulation in Older Adult, but no significant changes were observed in Adult Menthol. CONCLUSION: 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.

Change in EMG with skin friction at different frequencies during elbow flexion.

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.

Effect of submaximal isometric wrist extension training on grip strength.

Gripping force is produced by co-contraction of forearm flexors and extensors. Activation of extensors is important for stabilizing the wrist during gripping. However, forearm muscle function is complicated and the neurophysiological mechanism responsible for the gain in gripping force is unclear. Therefore, the purpose of this study was to investigate whether increasing forearm extensor activation with isometric wrist extension training has an effect on gripping force. Thirteen healthy subjects participated in this study. Maximal voluntary contraction of gripping was measured using a piezosensor (MVC(grip)) and EMG of forearm muscles at every wrist angle (from 70° flexion to 80° extension with 10° intervals) were measured simultaneously at baseline, 4 weeks, and 8 weeks after training. Training consisted of 30 repetitions equal to 70% MVC of isometric wrist extension for 8 weeks (5/week) on the right side. Gripping force was measured on both sides using a grip dynamometer without wrist angle restriction. Gripping force, EMG, maximal wrist extension force, and wrist angle-gripping force curve were investigated after training. After training, maximal wrist extension force increased significantly. Gripping force on the trained side also increased significantly. The training changed wrist angle at peak of MVC(grip). EMG activation of forearm extensors increased and that of flexors decreased during gripping. These results suggest that wrist extension training leads to an increase in gripping force and changes the balance of EMG activation between forearm flexors and extensors during gripping. Therefore, this training method should be useful as a therapeutic strategy for increasing grip strength.

Modulation of pre-programmed muscle activation and stretch reflex to changes of contact surface and visual input during movement to absorb impact.

The purpose of this study was to examine the extent of modification of the preactivation and stretch reflex response in ankle joint muscles to different contact surfaces and visual input during movement to absorb impact. Experimental movements like landing were performed using a special sliding apparatus. Seven subjects made landings on the hard surface (Hard-S) of a metal force platform or soft surface (Soft-S) of a foam cushion with eyes open or closed. The electromyographic activities from the medial gastrocnemius (MG), soleus (Sol), and tibialis anterior (TA) muscles, contact force, and ankle joint angle were recorded. The preactivation levels of MG and TA to Hard-S increased compared to Soft-S. After foot contact, dorsiflexion velocity, impulse, and responses of the stretch reflex in MG and Sol were significantly larger on Hard-S than Soft-S. With eyes closed, there were trends of decrease in the preactivation. Although the dorsiflexion velocity and impulse showed no significant differences between both visual conditions, the stretch reflex responses with eyes closed were larger than those with eyes open for both surfaces. These results suggest that the preactivation is modulated to different surface and the reflex gain is enlarged by visual suppression.

Increase in rate of force development with skin cooling during isometric knee extension.

Rate of force development (RFD) plays an important role when performing rapid and forceful movements. Cold-induced afferent input with transient skin cooling (SC) can modulate neural drive. However, the relationship between RFD and SC is unknown. The purpose of this study was to investigate whether SC increases RFD during isometric knee extension. Fifteen young healthy men (25 ± 8 yrs old) contracted their quadriceps muscle as fast and forcefully as possible with or without SC. Skin cooling was administered to the front of the thigh. Torque and electromyographic activity were measured simultaneously. Peak torque was not affected by SC. Skin cooling induced a significant increase in RFD at the phase 0-30 and 0-50 ms. The root mean square of the electromyography of vastus medialis, rectus femoris and vastus lateralis at the phases 0-30-50-100 ms increased significantly or tended to increase with SC. These results suggest that SC may increase neural drive and improve RFD in the very early phases of contraction.