Limb proprioception is an awareness by the central nervous system (CNS) of the location of a limb in three-dimensional space and is essential for movement and postural control. The CNS uses the position of the head and neck when interpreting the position of the upper limb, and altered input from neck muscles may affect the sensory inputs to the CNS and consequently may impair the awareness of upper limb joint position. The purpose of this study was to determine whether fatigue of the cervical extensors muscles (CEM) using a submaximal fatigue protocol alters the ability to recreate a previously presented elbow angle with the head in a neutral position. Twelve healthy individuals participated. CEM activity was examined bilaterally using surface electromyography, and kinematics of the elbow joint was measured. The fatigue protocol included an isometric neck extension task at 70 % of maximum until failure. Joint position error increased following fatigue, demonstrating a significant main effect of time (F 2, 18 = 19.41, p ≤ 0.0001) for absolute error. No significant differences were found for variable error (F 2, 18 = 0.27, p = 0.76) or constant error (F 2, 18 = 1.16 of time, p ≤ 0.33). This study confirms that fatigue of the CEM can reduce the accuracy of elbow joint position matching. This suggests that altered afferent input from the neck subsequent to fatigue may impair upper limb proprioception.

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Force modulation relies on accurate proprioception, and force-matching tasks alter cortico-cerebellar connectivity. Cortico-cerebellar (N24) and cortico-motor pathways are impacted following acquisition of a motor tracing task (MTT), measured using both somatosensory evoked potentials (SEPs) and transcranial magnetic stimulation. This study compared changes in early SEP peak amplitudes and motor performance following a force matching tracking task (FMTT) to an MTT. 30 (18 females) right-handed, participants aged 21.4 ± 2.76, were electrically stimulated over the right-median nerve at 2.47 Hz and 4.98Hz (Averaged 1000 sweeps/rate) to elicit SEPs, recorded via a 64-channel electroencephalography cap, pre and post task acquisition using the right abductor pollicis brevis muscle. Retention was measured 24 hours later. Significant time by group interactions occurred for the N20 SEP: 6.3% decrease post FMTT vs 5.5% increase post MTT (p = 0.013). P25 SEP: 4.0 % decrease post FMTT vs 10.3% increase post MTT (p = 0.006). N18 SEP 113.4 % increase post FMTT vs 4.4 % decrease post MTT (p = 0.006). N18 and N30 showed significant effect of time (both p < 0.001). Motor Performance: Significant time by group interactions - post-acquisition: FMTT improved 15.3% vs 24.3% for MTT (p = 0.025), retention: FMTT improved 17.4 % and MTT by 30.1% (p= 0.004). Task-dependent differences occurred in SEP peaks associated with cortical somatosensory processing (N20 and P25), and cerebellar input (N18), with similar changes in sensorimotor integration (N30), with differential improvements in motor performance, indicating neurophysiological differences in cerebellar and sensory processing for tasks reliant on proprioception.

The cerebellum undergoes neuroplastic changes in response to motor learning. Healthy human individuals demonstrate reduced cerebellar inhibition (CBI) following motor learning. Alterations in neck sensory input due to muscular fatigue are known to impact upper limb sensorimotor processing, suggesting that neck fatigue may also impact cerebellum to motor cortex (M1) pathways in response to motor learning. Therefore, this study aimed to determine whether cervical extensor muscle (CEM) fatigue alters CBI in response to motor learning. We examined sixteen participants (8 CEM fatigue and 8 CEM control). A double cone TMS coil stimulated the ipsilateral cerebellar cortex 5 ms prior to application of contralateral test stimuli of the M1 to the right first dorsal interosseous muscle. Cerebellar-MI activity curves were established pre- and post- motor skill acquisition (consisting of tracing sinusoidal-pattern waves with the index finger), and following either the CEM fatigue or control intervention. The control group showed greater cerebellar disinhibition than the fatigue group following motor skill acquisition (p<0.006), while the fatigue group showed similar levels of CBI pre- and post-motor skill acquisition. Both groups improved in accuracy following acquisition (p= 0.012), and retention (p= 0.007), but the control group improved significantly more (17% at acquisition and 22% at retention) vs lower (6% and 9%) improvements for the fatigue group. Lessened cerebellar disinhibition in the CEM fatigue vs. control group, coupled with diminished motor learning, suggests that CEM fatigue affects the cerebellar-MI interaction, influencing the cerebellum's ability to adjust motor output to acquire and learn a novel motor task.