Hoffmann Reflex Measured Reliably From Lateral Gastrocnemius Muscle Among Older People With Peripheral Neuropathy

PURPOSE: To examine the test-retest reliability of H-reflex testing in the soleus (SOL), the medial (MG), and the lateral gastrocnemius (LG) muscles during both standing and walking conditions among elderly with peripheral neuropathy (PN). METHODS: This study recruited sixteen participants with physician-diagnosed PN and impaired foot sole cutaneous sensation (inability to detect the 5.07-gauge monofilament at three or more of ten total tested sites). The H-reflex was elicited using an electrical stimulator with a cathode placed on the popliteal fossa and anode placed over the patella of the same leg. The H-wave and M-wave were recorded by EMG Works at a sampling rate of 2,000 Hz with EMG electrodes placed on the muscle belly of SOL, MG, and LG muscles. For the standing condition, a 500 μs square-pulse single stimulus started at 5 mA and increased with 2 mA increments to elicit H-reflex until the maximum M-wave was reached. For the walking condition, consistent stimulus intensity that elicited 15% of maximum M-wave during stance was used to elicit H-reflex, which was recorded at the heel contact, midstance, and toe-off phases, respectively. All measurements were collected on two separate occasions with at least 7 days apart. The test-retest reliability of the H-index and H/M ratio was examined using intraclass correlation coefficients (ICC) with a two-way mixed model. RESULTS: The H-reflex was successfully elicited from 12 of 16 participants (5 females, age: 71.5 ± 4.8 years, height: 170.0 ± 10.0 cm, body mass: 89.3 ± 21.4 kg). The ICCs of H-index during standing and walking conditions were poor to moderate in SOL (0.486-0.737) and MG (0.221-0.768), and moderate to high in LG (0.713-0.871). The ICCs of H/M ratio were poor to moderate reliability in SOL (0.263-0.702) and MG (0.220-0.733), and high reliability in LG (0.856-0.958) during standing and walking. CONCLUSIONS: The H-reflex measured from LG muscle is more reliable than from SOL and MG muscles during standing and walking conditions among older people with PN. LG muscle provides a reliable window on central modulation of the peripheral nervous system through H-reflex.