Sex Differences in Heart Rate Response to Isometric Handgrip Exercise with Concurrent Contralateral Forearm Somatosensory Stimulation

Abstract

BackgroundPharmacological evidence indicates that baseline cardiovagal mechanisms determine the rapid heart rate (HR) response to the onset of moderate intensity isometric handgrip (IHG) exercise. The HR response at exercise onset expresses sex differences, being less in females. Further, somatosensory nerve stimulation (STIM) appears to affect baseline cardiovagal control in some supine participants.ObjectiveThis study explored the effect of STIM on HR and heart rate variability (HRV) during short‐duration moderate‐intensity IHG in supine healthy adults and explored whether this effect expresses sex differences.ParticipantsTwenty‐four young healthy individuals aged 23 ± 1.9 years (18 females (F): 165 ± 7.4cm, 63 ± 13kg, BMI 23 ± 2kg/m2; 6 males (M): 179 ± 2.2cm, 79 ± 11kg, BMI 25 ± 3.3kg/m2).MethodsParticipants performed six isometric handgrips with their right hand at 30 to 40% of their maximal grip strength, each lasting 20 to 30 seconds and separated by one minute of rest. Three of these IHG contractions were performed during simultaneous administration of sub‐motor STIM provided by transcutaneous electrical nerve stimulation (TENS; 100 Hz, 50 μs) on the medial contralateral forearm through anesthetized skin for the duration of the handgrip. A 3‐lead ECG provided R‐R interval data. Systolic (SBP) and diastolic blood pressure (DBP) were monitored, as well as, heart rate (HR), root mean square of successive differences in R‐R intervals (RMSSD) as a measure of HRV, and respiration. Data were analysed using two‐factor ANOVA with Bonferroni correction, and independent t‐tests.ResultsThe ΔHR from baseline to IHG without STIM was greater in males compared to females (12 ± 6bpm versus 6 ± 6bpm, respectively; d = 1.00). No differences in ΔHR were detected for either sex when STIM was added to the IHG. Of the 18 F participants, 4 provided a minimal HR response (ΔHR > 4bpm) to the IHG without STIM (F1: 77 to 79bpm; F2: 69 to 70 bpm; F3: 50 to 50bpm; F4: 62 to 62 bpm) which resolved in 3 of the 4 F participants with application of STIM (F1:73 to 83bpm; F3: 45 to 59bpm; F4: 54 to 60bpm). Further, no statistically significant differences were observed in ΔRMSSD from baseline to IHG without STIM (p = 0.0321; M: 77 ± 68ms to 30 ± 145ms; F: 74 ± 38ms to 54 ± 39ms) and with STIM (p = 0.953; M: −28 ± 61ms and F: −30 ± 21ms).ConclusionOur preliminary findings suggest that, in supine individuals, sex differences exist in the HR response at the exercise onset but these effects are not modified by concurrent sub‐motor somatosensory nerve stimulation.Support or Funding InformationSupported by Natural Science and Engineering Research Council of CanadaThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.