Effect of a graded running race on lower limb muscle damage, jump performance and muscle soreness in men and women.

PURPOSE: Delayed structural and functional recovery after a 20 km graded running race was analyzed with respect to the sex effect. METHODS: Thirteen female and 14 male recreational runners completed the race and three test sessions: one before (PRE) and two after, once on Day 1 or 2 (D1-2) and then on Day 3 or 4 (D3-4). Muscle damage was assessed indirectly using ultrasonography to quantify changes in cross-sectional area (CSA) of 10 lower-limb muscles. Delayed onset of muscle soreness (DOMS) was assessed for three muscle groups. Functional recovery was quantified by kinetic analysis of a squat jump (SJ) and a drop jump (DJ) test performed on a sledge ergometer. Linear mixed models were used to assess control group reproducibility and recovery patterns according to sex. RESULTS: Regardless of sex, DOMS peaked at D1-2 for all muscle groups and resolved at D3-4. CSA was increased in each muscle group until D3-4, especially in the semimembranosus muscle. A specific increase was found in the short head of the biceps femoris in women. Regardless of sex, SJ and DJ performances declined up to D3-4. Depending on the muscle, positive and/or negative correlations were found between structural and functional changes. Some of these were sex-specific. CONCLUSION: Structural and functional recovery was incomplete in both sexes up to D3-4, although DOMS had disappeared. More emphasis should be placed on hamstring muscle recovery. Highlighting the intermuscular compensations that can occur during multi-joint testing tasks, the structural-functional relationships were either positive or negative, muscle- and sex-dependent.

Muscle synergies inherent in simulated hypogravity running reveal flexible but not unconstrained locomotor control.

With human space exploration back in the spotlight, recent studies have investigated the neuromuscular adjustments to simulated hypogravity running. They have examined the activity of individual muscles, whereas the central nervous system may rather activate groups of functionally related muscles, known as muscle synergies. To understand how locomotor control adjusts to simulated hypogravity, we examined the temporal (motor primitives) and spatial (motor modules) components of muscle synergies in participants running sequentially at 100%, 60%, and 100% body weight on a treadmill. Our results highlighted the paradoxical nature of simulated hypogravity running: The reduced mechanical constraints allowed for a more flexible locomotor control, which correlated with the degree of spatiotemporal adjustments. Yet, the increased temporal (shortened stance phase) and sensory (deteriorated proprioceptive feedback) constraints required wider motor primitives and a higher contribution of the hamstring muscles during the stance phase. These results are a first step towards improving astronaut training protocols.

Impact of occlusal proprioception on static postural balance.

Conflicting results on the effects of occlusal proprioceptive information on standing sway have been reported in the literature, partly due to the heterogeneity of the occlusal criterion studied and the experimental protocol used. In this study, occlusal functions, different mandibular positions and visual conditions were used to investigate the involvement of occlusal proprioception information in static postural balance. Postural adjustments of 26 healthy young adults, divided into Class I malocclusion and Class I normocclusion groups, were studied in upright position, in five mandibular positions (1 free, 2 centric and 2 eccentric), with and without vision. Due to different reported test durations, postural parameters were examined for the first and last halves of the 51.2 s acquisition time. A permutation ANOVA with 4 factors was used: group, mandibular position, vision, time window. Mean length of CoP displacement was shorter with vision (ES = 0.30) and more affected by vision loss in the free than in the intercuspal mandibular position (ES = 0.76 vs. 0.39), which has more tooth contacts. The malocclusion group was more affected by vision loss (ES = 0.64). Unexpectedly, with vision, the mean length was smaller in one eccentric occlusion side compared to the other (ES = 0.51), but independent of the left or right side, and more affected by vision loss (ES = 1.04 vs. ES = 0.71). The first-time window of the acquisition time, i.e. 25.6 s, was sufficient to demonstrate the impact of dental occlusion, except for the sway area. Comparison of the two visual conditions was informative. With vision, the weight of occlusal proprioception was not strictly related to occlusal characteristics (number of teeth in contact; centered or eccentric mandibular position), and it was asymmetrical. Without vision, the lack of difference between groups and mandibular positions suggested a sensory reweighting, probably to limit postural disturbance.

Neuromuscular adjustments to unweighted running: the increase in hamstring activity is sensitive to trait anxiety.

Introduction: Originally developed for astronauts, lower body positive pressure treadmills (LBPPTs) are increasingly being used in sports and clinical settings because they allow for unweighted running. However, the neuromuscular adjustments to unweighted running remain understudied. They would be limited for certain lower limb muscles and interindividually variable. This study investigated whether this might be related to familiarization and/or trait anxiety. Methods: Forty healthy male runners were divided into two equal groups with contrasting levels of trait anxiety (high, ANX+, n = 20 vs. low, ANX-, n = 20). They completed two 9-min runs on a LBPPT. Each included three consecutive 3-min conditions performed at 100%, 60% (unweighted running), and 100% body weight. Normal ground reaction force and electromyographic activity of 11 ipsilateral lower limb muscles were analyzed for the last 30 s of each condition in both runs. Results: Unweighted running showed muscle- and stretch-shortening cycle phase-dependent neuromuscular adjustments that were repeatable across both runs. Importantly, hamstring (BF, biceps femoris; STSM, semitendinosus/semimembranosus) muscle activity increased during the braking (BF: +44 ± 18%, p < 0.001) and push-off (BF: +49 ± 12% and STSM: +123 ± 14%, p < 0.001 for both) phases, and even more so for ANX+ than for ANX-. During the braking phase, only ANX+ showed significant increases in BF (+41 ± 15%, p < 0.001) and STSM (+53 ± 27%, p < 0.001) activities. During the push-off phase, ANX+ showed a more than twofold increase in STSM activity compared to ANX- (+119 ± 10% vs. +48 ± 27, p < 0.001 for both). Conclusion: The increase in hamstring activity during the braking and push-off phases may have accelerated the subsequent swing of the free-leg, likely counteracting the unweighting-induced slowing of stride frequency. This was even more pronounced in ANX+ than in ANX-, in an increased attempt not to deviate from their preferred running pattern. These results highlight the importance of individualizing LBPPT training and rehabilitation protocols, with particular attention to individuals with weak or injured hamstrings.

Sex influence on muscle synergies in a ballistic force-velocity test during the delayed recovery phase after a graded endurance run.

The acute and delayed phases of the functional recovery pattern after running exercise have been studied mainly in men. However, it seems that women are less fatigable and/or recover faster than men, at least when tested in isometric condition. After a 20 km graded running race, the influence of sex on the delayed phase of recovery at 2-4 days was studied using a horizontal ballistic force-velocity test. Nine female and height male recreational runners performed maximal concentric push-offs at four load levels a week before the race (PRE), 2 and 4 days (D2 and D4) later. Ground reaction forces and surface electromyographic (EMG) activity from 8 major lower limb muscles were recorded. For each session, the mechanical force-velocity-power profile (i.e. theoretical maximal values of force ( F ¯ 0), velocity ( V ¯ 0), and power ( P ¯ max)) was computed. Mean EMG activity of each recorded muscle and muscle synergies (three for both men and women) were extracted. Independently of the testing sessions, men and women differed regarding the solicitation of the bi-articular thigh muscles (medial hamstring muscles and rectus femoris). At mid-push-off, female made use of more evenly distributed lower limb muscle activities than men. No fatigue effect was found for both sexes when looking at the mean ground reaction forces. However, the force-velocity profile varied by sex throughout the recovery: only men showed a decrease of both V ¯ 0 (p < 0.05) and P ¯ max (p < 0.01) at D2 compared to PRE. Vastus medialis activity was reduced for both men and women up to D4, but only male synergies were impacted at D2: the center of activity of the first and second synergies was reached later. This study suggests that women could recover earlier in a dynamic multi-joint task and that sex-specific organization of muscle synergies may have contributed to their different recovery times after such a race.

Sex Differences in Endurance Running.

In recent years, there has been a significant expansion in female participation in endurance (road and trail) running. The often reported sex differences in maximal oxygen uptake (VO2max) are not the only differences between sexes during prolonged running. The aim of this narrative review was thus to discuss sex differences in running biomechanics, economy (both in fatigue and non-fatigue conditions), substrate utilization, muscle tissue characteristics (including ultrastructural muscle damage), neuromuscular fatigue, thermoregulation and pacing strategies. Although males and females do not differ in terms of running economy or endurance (i.e. percentage VO2max sustained), sex-specificities exist in running biomechanics (e.g. females have greater non-sagittal hip and knee joint motion compared to males) that can be partly explained by anatomical (e.g. wider pelvis, larger femur-tibia angle, shorter lower limb length relative to total height in females) differences. Compared to males, females also show greater proportional area of type I fibres, are more able to use fatty acids and preserve carbohydrates during prolonged exercise, demonstrate a more even pacing strategy and less fatigue following endurance running exercise. These differences confer an advantage to females in ultra-endurance performance, but other factors (e.g. lower O2 carrying capacity, greater body fat percentage) counterbalance these potential advantages, making females outperforming males a rare exception. The present literature review also highlights the lack of sex comparison in studies investigating running biomechanics in fatigue conditions and during the recovery process.

Sex Influence on the Functional Recovery Pattern After a Graded Running Race: Original Analysis to Identify the Recovery Profiles.

This study investigated the sex influence on the acute and delayed fatigue effects of a 20 km graded running race. Eighteen recreational runners, 10 women and 8 men, completed the race. The testing protocol included five sessions: a week before the race (PRE), 35 ± 15 min after (POST), 2 h, 2 and 4 days (2D and 4D) later. Each session included uni- and bilateral maximal isometric voluntary contractions of the knee extensors (MVC), a squat jump (SJ), and a drop jump (DJ). Acute and delayed muscle soreness (DOMS) were evaluated for the quadriceps, hamstring and triceps surae muscle groups. The 2D and 4D sessions included also a horizontal force-velocity test (HF-V) performed under five resistive conditions. For each test, a set of key variables was computed to characterize the lower limb functional recovery. Mixed ANOVA analyses revealed significant (sex × time) interactions, with larger acute drops for men in MVCs and earlier recovery for women in the bilateral MVC (p < 0.001) and DJ (p < 0.05) tests. Only women reported DOMS for the hamstrings at 2D (p < 0.001) and showed small improvements in pure concentric SJ (p < 0.05) and HF-V (p < 0.01) tests at 4D. As expected, DOMS disappeared prior to the complete functional recovery. These results confirmed the combined influence of testing task and sex on the functional recovery pattern while supporting a lesser and faster recovery in women. The originality of this study lies in the complexity and sex-dependence of the functional recovery pattern revealed by a multiple factorial analysis which was used to identify the most discriminating tests and variables in the recovery pattern. The obtained clusters highlighted some recovery profiles associated with greater risks of injury when starting to run again. However, the lack of sex × time interaction for normalized values emphasizes the major influence of men's initially higher functional values compared to women.