Diurnal changes in the amplitude of the Hoffmann reflex in the human soleus but not in the flexor carpi radialis muscle

Abstract

Changes in the reflex amplitude throughout the day have been observed in non-human mammals. The present experiment tested whether diurnal fluctuations also occur in humans. Hoffmann reflex (H-reflex) amplitude was measured in soleus and flexor carpi radialis (FCR) muscles from the data collected over a 12-h period between 7:00-9:00 a.m. and 7:00-9:00 p.m. At 4-h intervals, M/H recruitment curves were obtained, and two measures of H-reflex excitability were calculated. The maximal H-reflex (H (max)) was calculated as the average of the three largest H-reflexes. H-reflexes were also sampled from the ascending limb of the M/H recruitment curve (H (A), n=10), with a corresponding M-wave of 5% M (max). All values were normalized to the maximal M-wave (M (max)). Soleus H-reflex amplitude and plantar flexion maximal voluntary isometric contraction force (MVIC) were significantly smaller (p<0.05) in the morning (H (max)=57.2% M (max), H (A)=42.3%, M (max), MVIC=162.1 Nm) than in the evening (H (max)=69.1% M (max), a 20.1% increase, H (A)=54.1% M (max), a 27.4% increase and MVIC=195.8 Nm, a 20.8% increase). In contrast, FCR H-reflex amplitude and FCR MVIC were unchanged across all testing sessions. The data show that diurnal fluctuations are present in the amplitude of the human soleus but not in the FCR H-reflex. Diurnal fluctuation in the human soleus H-reflex amplitude must be considered when interpreting H-reflex data, especially when a repeated measures design spanning several days is utilized.

Chronotype Influences Diurnal Variations in the Excitability of the Human Motor Cortex and the Ability to Generate Torque during a Maximum Voluntary Contraction

“…Hence, our data suggest that the previously identified diurnal rhythm in spinal excitability (Lagerquist et al, 2006) is independent of chronotype. We also used the H max :M max ratio as a measure of spinal excitability and found that it did not change over the day.…”

“…We hypothesized that changes in the excitability of the motor cortex and spinal cord would mirror patterns in torque production (i.e., increased excitability at 9:00 for morning people and at 21:00 for evening people). We did not expect to find changes at the level of the muscle over the day since previous studies have found no such changes for the muscles that plantar-flex the ankle (Guette et al, 2006;Lagerquist et al, 2006).…”

Long-Term Plasticity in Reflex Excitability Induced by Five Weeks of Arm and Leg Cycling Training after Stroke

“…The post-test following training was performed within three days of the last exercise session. At these sessions, the same tests were performed in the same order and environmental conditions (i.e., temperature, noise, lighting, participant position) and session time of day were kept as consistent as possible [53,54,55]. This design allowed for the creation of a reliable and consistent pretest measure that allowed for inspection of spontaneous recovery effects, and provided baseline data against which changes were evaluated.…”

Acquisition of a Simple Motor Skill: Task-Dependent Adaptation Plus Long-Term Change in the Human Soleus H-Reflex

“…Follow-up Sessions occurred 10–14 days, one month, two months, and three months after the final Conditioning Session. To prevent the normal diurnal variation in H-reflex size (Wolpaw and Seegal, 1982; Chen and Wolpaw, 1994; Carp et al, 2006b; Lagerquist et al, 2006) from affecting the results, a subject’s sessions always occurred at the same time of day (i.e., within the same 3-hr time window). Each session lasted 60–90 min.…”