Priscila Torrado

Objectives: We examined the effects of sex and inertia on within-session reliability of flywheel half-squat performance outcomes. Methods: A total of 21 males and 25 females (aged 24.9 and 23.6, respectively) performed two sets of six valid repetitions using four inertial loads. Mean force, mean and peak power, impulse, and work were recorded during concentric and eccentric phases. Intraclass correlation coefficient (ICC), coefficient of variation (CV), typical error (TE), smallest worthwhile change (SWC), and minimal detectable change were calculated. A three-way repeated measures ANOVA was used to identify systematic differences and interaction effects. Results: Regardless of inertia or contraction phase, both males and females demonstrated excellent between-set reliability (ICC > 0.803 in males and superior to 0.946 in females) across all variables. Although males showed slightly higher CV values, CVs were good for all variables (≤9%). Overall, good sensitivity (SWC > TE) was observed in the four inertias, with marginal sensitivity (TE > SWC) more frequently observed for the power-related outcomes. Whereas no interactions between Sex × Set × Inertia were observed among the variables, significant interactions between Inertia × Sex were observed in both contraction phases for power-related variables (eccentric peak power, p < 0.001; concentric mean power, p = 0.032). Conclusions: reliability was excellent across all moments of inertia and contraction phases for both sexes, highlighting the importance of considering inertia configuration and sex differences when profiling performance outcomes.

Sex-based differences in performance fatigability during maximal dynamic tasks using FD have not yet been investigated. Immediately after the task, central fatigue was comparable between sexes; however, males exhibited greater deficits in contractile function. Standing out is that contractile impairment persisted in both groups at 10-min postexercise.

Background: Isometric and dynamic tasks of low-to-moderate intensities have been used to study sex differences in fatigability; however, maximal exertions with flywheel devices (FDs) have not been used. This study aimed to (1) detect sex differences in fatigue-related performance in a maximal intermittent fatiguing protocol on a FD, and (2) investigate the most sensitive dynamometric and mechanical variables for assessing fatigue in both sexes. Hypothesis: No sex differences should exist when performing this protocol on a FD. Study Design: Cohort observational study. Level of Evidence: Level 3. Methods: A total of 34 young adults (17 female/17 male) performed 10 sets of 10 repetitions with 3 minutes of passive recovery of a half-squat exercise on a FD. Inter- and intraset analysis of force, power, velocity, work, and impulse, together with their relative change and slope, were calculated during concentric and eccentric phases. Raw data were also normalized to body mass in the interset analysis. The relative changes in each variable were compared. Results: Men showed greater and earlier decreases in performance throughout sets ( P < .05; η _p ² ≥ 0.08), but these differences were not consistent after normalization for body mass ( P > .05; η _p ² ≤ 0.05). Irrespective of sex and phase, the intraset analysis revealed that relative change was higher in the last set ( P ≤ .03; η _p ² ≥ 0.14), with power being the most sensitive variable for detecting performance decline ( P ≤ .04; η _p ² = 0.49). Conclusion: Women experienced slower and delayed fatigue kinetics than men during a maximal intermittent fatiguing protocol with FD if body dimensionality is not considered. For training purposes, power seems to be the most sensitive and discriminative variable for detecting decreases in performance. Clinical Relevance: Body dimensionality is a key factor that must be considered when comparing both sexes in FDs.

Purpose: To study the possible sex differences in muscle activity after a maximal intermittent fatiguing protocol (IFP_max) performed with a flywheel device. Methods: Fifteen males and 17 females completed 10 sets of 10 half-squat repetitions with 3 minutes of passive recovery between sets as the IFP_max. Before and after the IFP_max, maximal isometric half-squat and countermovement jump were performed. Surface electromyography was used to analyze muscle activity in the gluteus maximus, vastus lateralis, rectus femoris, vastus medialis, biceps femoris, and semitendinosus. Results: Both sexes exhibited a similar decline in maximal isometric half-squat force and countermovement-jump flight time after the IFP_max. Although males demonstrated higher baseline power performance (F ≥ 4.99, P ≤ .013, ), these differences were no longer significant at the end of the fatiguing protocol. A more pronounced decrease in electromyography activity of the agonist musculature was observed in males (F ≥ 4.84, P ≤ .036, ), whereas delta analysis revealed a greater increase in antagonist muscle activity in females (P < .05). Hip-to-knee cocontraction ratio increased similarly in both sexes (F ≥ 10.14, P ≤ .004, ). However, males and females adopted distinct muscle-activation patterns as fatigue developed. Conclusions: Sex-related differences in muscle activity following an IFP_max performed with a flywheel device suggest the potential for higher training volumes and/or shorter recovery intervals for females. These findings provide valuable insights for the individualization and optimization of training protocols based on sex differences.

Purpose: To verify whether training the iron cross (IC) with assistive devices (herdos; H_IC) and added external load (LH_IC) to equate the moments of force developed on the rings could be considered an intermediate step between the nonoverloaded herdos situation (H_IC) and the IC performed on the rings. Methods: Relative levels of surface electromyography (sEMG) activity were normalized with respect to a standing IC before comparing gymnasts who can perform the IC on the rings (achievers) and gymnast who cannot (nonachievers) in the 2 herdos conditions (H_IC and LH_IC). Seven muscles were chosen for sEMG analysis, namely, pectoralis major (PM), latissimus dorsi, teres major, lower trapezius, serratus anterior, biceps brachii (BB), and triceps brachii. Additionally, 3 indices were calculated to measure levels of coactivation: Elbow_idx, Scapula_idx, and Shoulder_idx. Results: The bigger magnitude of differences in sEMG activity among situations was found for the PM and BB (F ≥ 30.7; P < .001). When comparing the global and the PM, teres major, BB, and triceps brachii activity across groups, nonachievers activated their musculature to a greater extent than the achievers independently of the herdos situation (P ≤ .046). Achievers’ Elbow_idx was the only index that was significantly higher (P ≤ .005) in the IC in comparison to LH_IC and H_IC. Conclusion: sEMG activity of PM and BB was particularly sensitive between situations, independently of the level of achievement. We recommend training the IC by adding external load in the herdos situation to increase muscle activity to levels closer to the rings situation but avoiding the potential factor of injuries.

Despite a reduction in the maximal voluntary isometric contraction (MVC_isom) observed systematically in intermittent fatigue protocols (IFP), decrements of the median frequency, assessed by surface electromyography (sEMG), has not been consistently verified. This study aimed to determine whether recovery periods of 60 s were too long to induce a reduction in the normalized median frequency (MF_EMG) of the flexor digitorum superficialis and carpi radialis muscles. Twenty-one road racing motorcycle riders performed an IFP that simulated the posture and braking gesture on a motorcycle. The MVC_isom was reduced by 53% (p < 0.001). A positive and significant relationship (p < 0.005) was found between MF_EMG and duration of the fatiguing task when 5 s contractions at 30% MVC_isom were interspersed by 5 s recovery in both muscles. In contrast, no relationship was found (p > 0.133) when 10 s contractions at 50% MVC were interspersed by 1 min recovery. Comparative analysis of variance (ANOVA) confirmed a decrement of MF_EMG in the IFP at 30% MVC_isom including short recovery periods with a duty cycle of 100% (5 s/5 s = 1), whereas no differences were observed in the IFP at 50% MVC_isom and longer recovery periods, with a duty cycle of 16%. These findings show that recovery periods during IFP are more relevant than the intensity of MVC_isom. Thus, we recommend the use of short recovery periods between 5 and 10 s after submaximal muscle contractions for specific forearm muscle training and testing purposes in motorcycle riders.

This case study was conducted to assess muscle pattern, as measured by surface electromyography (sEMG), and its changes during a controlled superbike closed-road track training session. The sEMG signals were recorded unilaterally from biceps brachii (BB), triceps brachii (TB), anterior and posterior part of the deltoid (DA and DP respectively), flexor digitorum superficialis (FS), extensor carpi radialis (CR), extensor digitorum communis (ED) and pectoralis major (PM) during three rounds of 30 min. sEMG signals selected for analysis came from the beginning of the braking action to the way-out of the curves of interest. Considering the laps and rounds as a whole and focusing on the forearm muscles, ED was more systematically (84%) assigned to a state of fatigue than FS (44%) and CR (39%). On the opposite, the TB and DP muscles showed a predominant state of force increase (72%). Whereas the BB showed alternatively a state of fatigue or force increase depending on the side of the curve, when taking into account only the sharpest curves, it showed a predominant state of force increase. In conclusion, the fact that forearm muscles must endure a long-lasting maintenance of considerable activity levels explains why they easily got into a state of fatigue. Moreover, TB and DA are particularly relevant when cornering.

Maneuvering a motorcycle in racing conditions or for prolonged time is sufficiently demanding that on many occasions forearm muscles reach a state of functional failure when riders cannot properly brake or operate the throttle. This study intends to discriminate which ones of the several dynamometric parameters used in the literature to characterize the Force-time (F-t) curve during voluntary contractions are more sensitive to neuromuscular fatigue in simulated motorcycle-riding conditions. Thirty-three adults performed an intermittent fatiguing protocol (IFP) that simulated the brake-pulling and throttle-twisting actions, by using a hydraulic system equipped with a pressure sensor. Sixty pressure-time (P-t) curve parameters, including the rate of pressure development (RPD) and area under the curve were measured to characterize the time course of the braking maximal voluntary contraction (MVC). Two types of variables were used to analyze the P-t curve: 1) Times interval (from 0 to 30-50-100-500-1000 and 2000 ms); 2) Percentages of MVC (10-30-60-90%MVC). Overall significant (p≤ 0.05) fatigue-related declines were observed only at time intervals longer than 100 ms and contraction intensities higher than 30%MVC. Strong and significant linear declines (p< 0.001) were observed at 500 ms and 1 s for normalized pressures, as well as for the ratio RPD_60%MVC/MVC (p< 0.003) throughout the IFP. Our results suggest considering RPD at time windows of 0–500 ms and 0–1 s, and contraction intensities comprised between 30% and 60% of MVC, as more suitable criteria to study fatigue-related decrements in performance rather than the classical MVC force.

Highly repetitive submaximal intermittent contractions of the forearm muscles during periods of 30–50 min partially explain why motorcycle races are so demanding for the neuromuscular system. This study investigated the contribution of central and peripheral mechanisms of fatigue on the exerted and contralateral extensor digitorum communis following an intermittent fatigue protocol (IFP) designed for motorcycle riders. 12 riders performed an IFP, which simulates the braking and throttle handle gesture. We examined the time course of recovery of maximal voluntary contraction (MVC), M-wave, motor evoked potential (MEP) to transcranial magnetic stimuli in relaxed and facilitated condition, and the cortical silent period (CSP) at time windows of 1, 3, 5, 10 and 20 min after the IFP. Whereas MVC, M-wave and MEP decreased, CSP lengthened significantly in the fatigued limb after completion of the IFP. Nevertheless, no differences were observed in the contralateral limb. All neurophysiological parameters reverted to baseline values in less than 20 min, while MVC remained lower in the exercised limb. No cross-over effects were observed in the contralateral non-exercised limb. Our results suggest that local factors are those mainly responsible for the incomplete MVC recovery after an intermittent muscle contraction protocol.

Fatigue in forearm muscles may be critical for motorcycle riders in relation to performance and forearm disorders. Force–time course parameters were examined to better characterize the reduction in the maximal force generating capacity (MVC) during an intermittent fatigue protocol (IFP) specifically designed for motorcycle riders. Also, a mathematical force fatigue model is proposed. Forty motorcyclists (aged 27.6 ± 6.8 years) performed an IFP that simulated the braking gesture and posture of a rider. Fatigue was confirmed by a 40% decrement of the normalized MVC in comparison with basal value. Contraction time increased in comparison with basal condition (P ≤ 0.034). Relaxation kinetics presented two phases: (a) a pre‐fatigue phase where half relaxation time (HRT_raw) and normalized (HRT_nor) decreased (P ≤ 0.013) while relaxation rate (RR_raw) remained unchanged; and (b) a fatiguing phase where HRT_raw, HRT_nor increased and RR_raw decreased (P ≤ 0.047). Normalized RR_raw (RR_nor) declined progressively (P ≤ 0.016). The proposed nonlinear force fatigue model confirmed a satisfactory adjustment (R² = 0.977 ± 0.018). This mathematical expression derived three patterns of force fatigue: three‐phase, exponential and linear, representing 70%, 13%, and 17% of the participants, respectively. Overall, these results provided further support to force fatigue theoretical and applied proposals.