Liam C. Tapsell

Objective: Evaluate the test–retest reliability of quadriceps corticospinal excitability and intracortical excitability using transcranial magnetic stimulation (TMS). Design: A test–retest observational cohort study. Methods: Twelve healthy adults attended two laboratory sessions, seated with their knee at 90 degrees and fitted with electrodes on the rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM). TMS was used to assess the active motor threshold (AMT), motor evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). Individual results were calculated as the mean and median of the 10 trials of each measure for MEP, SICI and ICF. Intraclass correlation coefficients were calculated. Results: All muscles showed good or excellent reliability for the mean and median measures of the MEP amplitude (ICC ≥ 0.820) as well as the AMT of the RF (ICC = 0.991). SICI showed good reliability in the mean and median measures of the RF and the mean measure of the VL (ICC ≥ 0.809), moderate reliability in both measures of the VM (ICC ≥ 0.655) and was not significant for the median measure of the VL (ICC = 0.513). ICF showed excellent reliability in the mean measure of each muscle and median measure of the RF (ICC ≥ 0.906), with good reliability in the median measure of the VL (ICC = 0.888) and moderate reliability in the median measure of the VM (ICC = 0.719). Conclusion: The mean of an individual’s quadriceps corticospinal excitability and intracortical excitability have good or excellent reliability for every TMS measure, in every muscle (except SICI of the VM). With the previous reliability of TMS measures mostly investigating the upper limbs, these results offer important context for neurophysiological research in the quadriceps.

Introduction : Motor cortex excitability may modulate muscle output and tissue sensitivity through complex neural interactions. While most research focuses on the upper limb, the lower limb is more relevant for physically active populations. Existing studies predominantly involve males, despite sufficient biological data suggesting sex differences may exist. Our study examined associations between corticospinal and intracortical excitability, quadriceps voluntary activation, and mechanical pain sensitivity in healthy, active females. Methods : Our cross-sectional study included physically active females >18 years. Quadriceps strength was measured with maximal voluntary contraction. Corticospinal/intracortical excitability were evaluated using transcranial magnetic stimulation (resting motor threshold, active motor threshold, short-interval intracortical inhibition, and intracortical facilitation) at rest and during 10% maximal voluntary contraction. Pressure pain threshold was measured at the hip and elbow. Quadriceps voluntary activation was assessed using twitch interpolation. Associations were analyzed using generalized estimating equations. Results : We included 29 females with a median [inter quartile range] age of 54 years [27.5–61.5]. Higher upper limb pressure pain threshold was associated with higher resting motor threshold (β = 0.87, p = .01) and active motor threshold (β = 1.92, p < .001), but not short-interval intracortical inhibition or intracortical facilitation. Lower limb pressure pain threshold showed no significant associations. Greater quadriceps voluntary activation was associated with lower resting motor threshold (β = −0.68, p < .001), lower active motor threshold (β = −0.83, p = .044), and lower short-interval intracortical inhibition (β = 30.75, p = .04), but not intracortical facilitation. Discussion : Corticospinal excitability and intracortical inhibition appear to be associated with voluntary activation and sensory processing differently. Upper limb pain sensitivity appeared to be associated with corticospinal excitability, whereas lower limb sensitivity did not, underscoring complex interactions.

Interhemispheric inhibition (IHI) acts between hemispheres to decrease motor cortical excitability. IHI changes during movement preparation, but it is unknown whether altering IHI, independent of other factors, alters movement initiation. For the index finger abductor muscle (first dorsal interosseous; FDI), IHI is weaker during contralateral index abduction than adduction. Thus, this study aimed to modulate IHI through contralateral contraction and measure resultant changes in reaction time. Fifteen healthy participants (age 19–39 years) completed a reaction-time task requiring brief left index finger abduction. Prior to reactions, participants started either a sustained isometric abduction or adduction contraction of the right index finger. Single- or paired-pulse transcranial magnetic stimulation (TMS) elicited motor evoked potentials (MEPs) from left FDI in the late pre-movement phase. For each contralateral contraction direction, unconditioned and conditioned MEPs (preceded by suprathreshold TMS over the other hemisphere at 10 or 40 ms) were recorded. Conditioned MEPs, expressed relative to unconditioned MEPs, provided measures of short-interval IHI (SIHI) and long-interval IHI (LIHI). Left index finger reaction time was also measured. Linear mixed models showed that reaction time was 9 ± 9 ms (6%) slower during right adduction than abduction (F_1,1875 = 30.7, p < 0.001). Unconditioned MEPs in left FDI were 1.1 ± 2.0 mV (37%) smaller (F_1,270 = 8.82, p = 0.003) and SIHI 11 ± 16% stronger during right adduction (F_1,279 = 15.15, p < 0.001). However, LIHI was not different between right contraction conditions (F_1,272 = 0.410, p = 0.522). These results suggest that IHI can alter reaction time by influencing corticospinal excitability. Stronger SIHI during right adduction likely delayed pre-movement increases in corticospinal excitability, slowing reaction time.

In mixed martial arts, punches commonly lead to a knockout (KO) or technical knockout (TKO), though factors influencing such punches are unclear. This study assessed how differences in height, reach, and combined difference (height + reach) influence fight-ending punches. We analysed 264 Ultimate Fighting Championship contests that concluded with a KO/TKO from hooks, straights, uppercuts, or overhand punches. Three multinomial logistic regression analyses assessed the influence of (a) reach, (b) height and (c) combined difference on likelihood of punch type, with overhand punches as the reference category. Pairwise comparisons for punch type were conducted, and probability differences were compared across the lower, middle, and highest point difference for reach (−20, 0, + 20 cm), height (−20, + 10, + 40 cm), and combined (−50, 0, + 50 cm). The punches with the highest frequency were hooks (51%) and straights (35%). For all models, the straight punch was more likely than the overhand (odds ratio: 1.06–1.10, p < 0.05). At 0 cm and 20 cm reach difference, the punch probability differences for straight and uppercut punches compared to uppercut and overhand was between 27–47% (p < 0.05). Similar findings were observed at +10 cm height difference, but at height +40 cm straights were 76% more likely than uppercuts and overhands (p < 0.05) for bouts that concluded with a KO/TKO. The combined model showed similar results to the reach model findings. These results can help inform coaches and fighters to prepare both offensive and defensive tactics by providing information on the most likely fight-ending punch depending on their specific matchups.