Effects of enhanced cutaneous sensory input on interlimb strength transfer of the wrist extensors

Abstract

The relative contribution of cutaneous sensory feedback to interlimb strength transfer remains unexplored. Therefore, this study aimed to determine the relative contribution of cutaneous afferent pathways as a substrate for cross‐education by directly assessing how “enhanced” cutaneous stimulation alters ipsilateral and contralateral strength gains in the forearm. Twenty‐seven right‐handed participants were randomly assigned to 1‐of‐3 training groups and completed 6 sets of 8 repetitions 3x/week for 5 weeks. Voluntary training (TRAIN) included unilateral maximal voluntary contractions (MVCs) of the wrist extensors. Cutaneous stimulation (STIM), a sham training condition, included cutaneous stimulation (2x radiating threshold; 3sec; 50Hz) of the superficial radial (SR) nerve at the wrist. TRAIN + STIM training included MVCs of the wrist extensors with simultaneous SR stimulation. Two pre‐ and one posttraining session assessed the relative increase in force output during MVCs of isometric wrist extension, wrist flexion, and handgrip. Maximal voluntary muscle activation was simultaneously recorded from the flexor and extensor carpi radialis. Cutaneous reflex pathways were evaluated through stimulation of the SR nerve during graded ipsilateral contractions. Results indicate TRAIN increased force output compared with STIM in both trained (85.0 ± 6.2 Nm vs. 59.8 ± 6.1 Nm) and untrained wrist extensors (73.9 ± 3.5 Nm vs. 58.8 Nm). Providing ‘enhanced’ sensory input during training (TRAIN + STIM) also led to increases in strength in the trained limb compared with STIM (79.3 ± 6.3 Nm vs. 59.8 ± 6.1 Nm). However, in the untrained limb no difference occurred between TRAIN + STIM and STIM (63.0 ± 3.7 Nm vs. 58.8 Nm). This suggests when ‘enhanced’ input was provided independent of timing with active muscle contraction, interlimb strength transfer to the untrained wrist extensors was blocked. This indicates that the sensory volley may have interfered with the integration of appropriate sensorimotor cues required to facilitate an interlimb transfer, highlighting the importance of appropriately timed cutaneous feedback.

A scoping review of the contralateral effects of unilateral peripheral stimulation on neuromuscular function

“…Among the 83 studies, 31 (37.3%) claimed that their aim was to examine the cross-education effects, with 10 studies examining acute effects of unilateral stimulation and 21 studies investigating the chronic effects of repeated unilateral stimulation. The aims, major findings, strength of the research design, and limitations as stated by the authors are summarised in Table 4 [ 12 , 19 – 21 , 23 – 25 , 41 , 52 , 54 , 57 , 62 , 64 , 69 – 71 , 77 , 80 , 91 , 96 , 97 , 99 , 100 , 103 , 105 , 107 – 110 , 113 , 114 ].…”

“…[ 65 , 73 , 76 ]. Few studies have attempted to identify what and how sensory inputs are involved in the manifestation of the contralateral effect [ 96 ], possibly due to the lack of a suitable methodology.…”

Indirect Vibration of the Upper Limbs Alters Transmission Along Spinal but Not Corticospinal Pathways

“…Trains of stimuli (5 × 1 ms @ 300 Hz) were applied to the superficial radial (SR) nerve just proximal to the radial head (Zehr and Hundza, 2005;Barss et al, 2020) were used to both condition H-reflexes and elicit cutaneous reflexes. A Grass S88 stimulator, SIU5 stimulus isolation and CCU1 constant current unit (Grass Instruments, Austin, TX, United States) (Nakajima et al, 2013) were used to deliver stimulation.…”

Exercise prescription and strategies to promote the cross-education of strength: a scoping review

“…The use of muscle, 8,37,39 nerve, 4 and brain 33 stimulation techniques in conjunction with unilateral training versus training alone show unique and somewhat conflicting results for the untrained limb. The studies investigating muscle stimulation have all done so for the knee extensors and show favorable 8,37 or similar 39,81 results on the magnitude of cross-education versus training alone.…”