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Ankle position and voluntary contraction alter maximal M waves in soleus and tibialis anterior
Author(s) -
Frigon Alain,
Carroll Timothy J.,
Jones Kelvin E.,
Zehr E. Paul,
Collins David F.
Publication year - 2007
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.20747
Subject(s) - ankle , soleus muscle , contraction (grammar) , tibialis anterior muscle , physical medicine and rehabilitation , muscle contraction , medicine , ankle dorsiflexion , anatomy , skeletal muscle
Compound muscle action potentials (CMAPs) recorded using surface electrodes are often used to assess the excitability of neural pathways to skeletal muscle. However, the amplitude of CMAPs can be influenced by changes at the recording site, independent of mechanisms within the central nervous system. We quantified how joint angle and background contraction influenced CMAP amplitude. In seven subjects CMAPs evoked by supramaximal transcutaneous electrical stimulation of motor axons (M max ) were recorded using surface electrodes from soleus and tibialis anterior (TA) at static positions over the full range of ankle movement at 5° intervals. Across subjects the peak‐to‐peak amplitude of M max was 155% and 159% larger at the shortest than longest muscle lengths for soleus and TA, respectively. In five subjects the effect of ankle position and voluntary contraction on M‐wave/H‐reflex recruitment curves was assessed in the soleus. Both ankle position and level of contraction significantly influenced M max , H max , and the H max to M max ratio, but there were no interactions between the two parameters. These peripheral changes that influence M max will also impact other CMAPs such as submaximal M‐waves, H‐reflexes, and responses to transcranial magnetic stimulation. As such, during experimental studies CMAPs evoked at a given joint angle and contraction level should be normalized to M max recorded at similar joint angle and contraction strength. Muscle Nerve, 2007