Motor unit firing rates of the gastrocnemii during maximal brief steady-state contractions in humans |
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Affiliation: | 1. Industrial and Management Systems Engineering, West Virginia University, P.O. Box 6070, Morgantown, WV 26506, USA;2. Industrial and Systems Engineering, Virginia Tech, 521 Whittemore Hall (0118), Blacksburg, VA 24061, USA;1. College of Automation and Electrical Engineering, Nanjing Tech University, Nanjing, 210009, China Tel: +86-25-85327246;7. Corresponding Author. The Chinese University of Hong Kong, Shenzhen, 2001 Longxiang Blvd., Longgang, Shenzhen, Guangdong, China. On leave from The University of Southern California, Los Angeles, CA 90089 USA |
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Abstract: | The human triceps surae (soleus, medial (MG) and lateral (LG) gastrocnemii) is complex and important for posture and gait. The soleus exhibits markedly lower motor unit firing rates (MUFRs; ∼16 Hz) during maximal voluntary isometric contraction (MVC) than other limb muscles, but this information is unknown for the MG and LG. During multiple visits, subjects performed a series of 5–7, ∼7-s plantar flexor MVCs with tungsten microelectrodes inserted into the MG and LG. During a separate testing session, another group of subjects performed submaximal isometric contractions at 25%, 50%, and 75% MVC with inserted fine-wires in the MG, LG and soleus. Maximum steady-state MUFRs for MG and LG (∼23 Hz) were not different, but faster than prior reports for the soleus. No differences between the three triceps surae components were detected for 25% or 50% MVC, but at 75% MVC, the MG MUFRs were 31% greater than soleus. The triceps surae exhibit similar torque modulation strategies at <75% MVC, but to achieve higher contraction intensities (>75% MVC) the gastrocnemii rely on faster rates to generate maximal torque than the soleus. Therefore, the MG and LG exhibit a larger range of MUFR capacities. |
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Keywords: | Triceps surae Isometric Motor neuron Rate coding |
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