The effect of vocalization on spinal excitation as measured by H wave

The aim of this study was to measure the H wave by using voice-activated electromyography to reveal how different speech outputs affect the spinal cord segments innervating the lower limb skeletal muscles. In 21 healthy adults (16 men and 5 women) seated in a semi-reclined position, the H wave was recorded using surface electrodes over the soleus muscle of the pivot leg after stimulating the tibial nerve. The amplitude of the H wave was 1.02 SD 0.69 mV under the pre-vocalization condition; 1.51 SD 0.76 mV under the submaximal vocalization condition (≥60-<80 dB); and 1.13 SD 0.59 mV under the maximal vocalization condition (≥80 dB), demonstrating that the amplitude generated with submaximal vocalization was significantly higher than the control and maximal vocalization conditions. Mean voice intensity was around 69 dB for submaximal vocalization and around 91 dB for maximal vocalization. Submaximal vocalization results in a higher H wave amplitude than the control condition, thus suggesting increased spinal cord excitation, which may be important for initiating activities of daily living (e.g., lifting objects) or mobility (e.g., moving from a sitting to a standing position).