Exercise-induced trunk fatigue decreases double poling performance in well-trained cross-country skiers

Influence of trunk muscle fatigue on lower limb asymmetries in novice runners

Running is generally considered a symmetrical activity that involves harmonized functions of upper and lower limbs. However, asymmetry can occur under certain conditions, such as fatigue, as lower limbs perform distinct functional tasks. While running, trunk muscles play a crucial role in transmitting loads between the upper and lower limbs, yet the impact of trunk muscle fatigue on the dominant and nondominant legs has not been well addressed. This study investigated the effects of trunk muscle fatigue on ground reaction force characteristics on dominant and nondominant legs in novice runners. Thirty participants were asked to run along a runway at 3.3 m · s-1 before and after a trunk muscle fatigue protocol. Ground reaction force data were collected bilaterally, and subsequent asymmetries were calculated. Trunk muscle fatigue had different effects on the dominant and nondominant legs. In the dominant leg peak medial force increased, while the nondominant leg showed reduced peak lateral force, peak braking force and peak negative free moment and increased medio-lateral impulse. Trunk muscle fatigue increased asymmetries in peak lateral force, peak braking force and decreased asymmetry in peak negative free moment. These findings suggest that trunk muscle fatigue, due to its different effects on dominant and nondominant legs, deteriorates running asymmetry and may increase injury risk in novice runners. Strengthening and improving the endurance of trunk muscles is recommended for novice runners to prevent strength reduction-related changes in running mechanics and mitigate injury risk.

Contribution of different strength determinants on distinct phases of Olympic rowing performance in adolescent athletes

Aerobic metabolism dominates Olympic rowing, but research on the relative contribution of strength and power demands is limited. This study aimed to identify the contribution of different strength determinants for distinct phases of rowing ergometer performance. The cross-sectional analysis comprised of 14 rowing athletes (4 female, 10 male, age: 18.8 ± 3.0y, 16.9 ± 2.2y). Measurements included anthropometrics, maximal strength of leg press, trunk extension and flexion, mid-thigh pull (MTP) and handgrip strength, VO2max, and a 2000 m time trial, where peak forces at the start, middle and end phase were assessed. Additionally, rate of force development (RFD) was assessed during the isometric leg press and MTP with intervals of 150, 350 ms and 150, 300 ms, respectively. Stepwise regression models for ergometer performance showed that the start phase was mainly explained by maximal trunk extension and RFD 300 ms of MTP (R2 = 0.91, p < 0.001) and the middle section by VO2max, maximal leg press strength and sitting height (R2 = 0.84, p < 0.001). For the end phase, a best fit was observed for trunk flexion, RFD 350 ms of leg press, body height and sex (R2 = 0.97 p < 0.001), whereas absolute VO2max, trunk flexion and sex explained variance over the entire 2000 m time trial (R2 = 0.98, p < 0.001). It appears that for the high acceleration in the start phase, force transmission through maximum strength for trunk extension is essential, while fast power production along the kinetic chain is also relevant. Additionally, the results support that maximal force complements the reliance on VO2max. Further intervention studies are needed to refine training recommendations.

DMC (2',4'-dihydroxy-6'-methoxy-3',5'-dimethylchalcone) enhances exercise tolerance via the AMPK-SIRT1-PGC-1α pathway in mice fed a high-fat diet

Obesity is caused by an imbalance between energy intake and energy expenditure. This study aimed to determine the effects and mechanisms of 2',4'-dihydroxy-6'-methoxy-3',5'-dimethylchalcone (DMC) on exercise tolerance in high-fat diet (HFD)-fed mice. Male C57BL/6J mice were randomly divided into two categories (7 groups [n = 8]): sedentary (control [CON], HFD, 200 mg/kg DMC, and 500 mg/kg DMC) and swimming (HFD, 200 mg/kg DMC, and 500 mg/kg DMC). Except the CON group, all other groups were fed HFD with or without DMC intervention for 33 days. The swimming groups were subjected to exhaustive swimming (three sessions/week). Changes in swimming time, glucolipid metabolism, body composition, biochemical indicators, histopathology, inflammation, metabolic mediators, and protein expression were assessed. DMC combined with regular exercise improved endurance performance, body composition, glucose and insulin tolerance, lipid profile, and the inflammatory state in a dose-dependent manner. Further, DMC alone or combined with exercise could restore normal tissue morphology, reduce fatigue-associated markers, and boost whole-body metabolism and the protein expression of phospho-AMP-activated protein kinase alpha/total-AMP-activated protein kinase alpha (AMPK), sirtuin-1 (SIRT1), peroxisome-proliferator-activated receptor gamma coactivator 1alpha (PGC-1α), and peroxisome proliferator-activated receptor alpha in the muscle and adipose tissues of HFD-fed mice. DMC exhibits antifatigue effects by regulating glucolipid catabolism, inflammation, and energy homeostasis. Furthermore, DMC exerts a synergistic exercise-related metabolic effect via the AMPK-SIRT1-PGC-1α signaling pathway, suggesting that DMC is a potential natural sports supplement with mimicked or augmented exercise effects for obesity prevention.

Chemical Characterization and Preliminary Evaluation of the Efficacy and Tolerability of a Food Supplement Based on Pomegranate Extract, B Vitamins, and Vitamin C against Prolonged Fatigue in Healthy Consumers

Fatigue, characterized by periods of exhaustion that interfere with normal activities and negatively affect quality of life, can be classified as prolonged fatigue (or short-term fatigue, SF) or chronic fatigue. Vitamin deficiency and chronic inflammation seem to be possible causes of fatigue. Due to the unavailability of effective remedies that attenuate fatigue and provide consumer satisfaction, the aim of this investigation is to assess whether a commercial food supplement consisting of pomegranate extract with known anti-inflammatory activity, B vitamins, and vitamin C can help fight SF. To this end, the chemical composition of whole fruit pomegranate dry extract was determined through a RP-UHPLC–HRMS method, which indicated the presence of ellagitannins, gallotannins, and organic and phenolic acids. In a survey of consumers of food supplements aimed at reducing fatigue, 78 subjects (21 men and 57 women) were recruited for one month to evaluate the efficacy and tolerability of this food supplement through validated questionnaires for assessing fatigue level and quality of life. The consumers reported a significant improvement in their conditions without adverse effects over this time period. Although further studies are needed, these preliminary data suggest the capacity of a combination of pomegranate extract and hydrosoluble vitamins to alleviate SF.

Exploring intensity-dependent modulations in EEG resting-state network efficiency induced by exercise

PURPOSE

Exhaustive cardiovascular load can affect neural processing and is associated with decreases in sensorimotor performance. The purpose of this study was to explore intensity-dependent modulations in brain network efficiency in response to treadmill running assessed from resting-state electroencephalography (EEG) measures.

METHODS

Sixteen trained participants were tested for individual peak oxygen uptake (VO2 peak) and performed an incremental treadmill exercise at 50% (10 min), 70% (10 min) and 90% speed VO2 peak (all-out) followed by cool-down running and active recovery. Before the experiment and after each stage, borg scale (BS), blood lactate concentration (BLa), resting heartrate (HRrest) and 64-channel EEG resting state were assessed. To analyze network efficiency, graph theory was applied to derive small world index (SWI) from EEG data in theta, alpha-1 and alpha-2 frequency bands.

RESULTS

Analysis of variance for repeated measures revealed significant main effects for intensity on BS, BLa, HRrest and SWI. While BS, BLa and HRrest indicated maxima after all-out, SWI showed a reduction in the theta network after all-out.

CONCLUSION

Our explorative approach suggests intensity-dependent modulations of resting-state brain networks, since exhaustive exercise temporarily reduces brain network efficiency. Resting-state network assessment may prospectively play a role in training monitoring by displaying the readiness and efficiency of the central nervous system in different training situations.

Effect of trunk muscles fatigue on plantar pressure distribution in novice runners

During running, trunk muscles act to sufficiently contribute to the energy generation and transmission of the body parts. Improper function of trunk muscles affects running mechanics adversely and could result in altered lower limb energetics. The aim of this study was to examine the effects of trunk muscles fatigue on plantar pressure distribution in novice runners. 46 novice heel-to-toe runners (26 female and 20 male) ran in 3.3 m/s before and after the trunk muscles fatigue along the plantar pressure measuring device. Then, participants performed trunk muscles fatigue protocol. Trunk muscles fatigue protocol consisted of four consecutive cycles of seven exercises (1) rotating trunk with a medicine ball in sitting position, 2) prone static torso extension with a medicine ball, 3) rotate lower torso with a medicine ball in supine position, 4) incline sit-ups with a weight plate, 5) lateral side binding with a weight plate, 6) rotating lumbar extension with weighted plate, and 7) standing trunk rotation with weighted pulley resistant. After trunk muscles fatigue, increases in loading of lesser toes (p = 0.001, ES = 0.379), fourth (p = 0.001, ES = 0.474) and fifth metatarsals (p = 0.004, ES = 0.173) and medial and lateral heel (p = 0.018,0.001, ES = 0.118,0.427) were observed. Also, foot progression angle (p = 0.001, ES = 392) and relative time of initial contact phase (p = 0.003, ES = 0.182) decreased. The trunk muscles fatigue could alter the plantar pressure distribution pattern. Novice runners should consider strengthening of the trunk region muscles to avoid trunk muscles strength reduction-related changes in running mechanics.

Performance-Determining Variables in Long-Distance Events: Should They Be Determined From a Rested State or After Prolonged Submaximal Exercise?

Performance-determining variables are usually measured from a rested state and not after prolonged exercise, specific to when athletes compete for the win in long-distance events.

PURPOSE

(1) To compare cross-country skiing double-poling (DP) performance and the associated physiological and biomechanical performance-determining variables between a rested state and after prolonged exercise and (2) to investigate whether the relationship between the main performance-determining variables and DP performance is different after prolonged submaximal DP than when tested from a rested state.

METHODS

Male cross-country skiers (N = 26) performed a blood lactate profile test and an incremental test to exhaustion from a rested state on day 1 (D1; all using DP) and after 90-minute submaximal DP on day 2 (D2).

RESULTS

The DP performance decreased following prolonged submaximal DP (D1: peak speed = 15.33-20.75 km·h-1, median = 18.1 km·h-1; D2: peak speed = 13.68-19.77 km·h-1, median = 17.8 km·h-1; z = -3.96, P < .001, effect size r = -.77), which coincided with a reduced submaximal gross efficiency and submaximal and peak cycle length, with no significant change in peak oxygen uptake (P = .26, r = .23). The correlation coefficient between D1 cycle length at 12 km·h-1 and D2 performance is significantly smaller than the correlation coefficient between D2 cycle length at 12 km·h-1 and D2 performance (P = .033), with the same result being found for peak cycle length (P < .001).

CONCLUSIONS

The reduced DP performance after prolonged submaximal DP coincided with a reduced submaximal gross efficiency and shorter peak cycle length. The results indicate that performance-determining variables could be determined after prolonged exercise to gain more valid insight into long-distance DP performance.

Trunk muscle activity during different types of low weighted squat exercises in normal and forefoot standing conditions

Squats are considered a useful basic exercise for trunk muscle activation. To gain knowledge about trunk muscle activity patterns depending on the barbell position in beginners, we examined squats with low weights in the back, front, and overhead position.

METHODS

Twelve healthy adults (6 women/6 men, age: 29.1 (SD 8.0) y, height: 173.4 (6.9) cm, body mass: 70.1 (9.1) kg) randomly performed the three barbell squats in normal and in forefoot standing. Surface electromyography from external (EO) and internal oblique, rectus abdominis, and erector spinae (ES) was recorded. The centre of pressure path length (CoP) and the motion of the lumbar spine were captured.

RESULTS

The overhead squat revealed the highest percent muscle activity, where EO (p = 0.009) and ES (p = 0.03) showed the greatest activity. Forefoot standing did not change overall trunk muscle activities (.05< Hedges' g <.29, 0.17 < p < 0.95) although longer CoP path length (.45 < g < 1.3, p < 0.05) was measured.

CONCLUSIONS

Squat exercises with low weight are useful to activate trunk muscles. Activity increases with the difficulty of the squat by frontal or overhead loading, but not by standing on the forefoot. The low weighted squat can target well core muscle activity in training with beginners or in rehabilitation.

Clinical reasoning framework for thoracic spine exercise prescription in sport: a systematic review and narrative synthesis

BACKGROUND

The thoracic spine is critical for athletic kinetic chain functioning yet widely overlooked in terms of specific evidenced-based exercise prescription. Thoracic mobility, motor control and strength are required to optimise performance in sport and minimise excessive load/stress on other components of the kinetic chain.

OBJECTIVE

To identify and evaluate mobility, motor control, work capacity and strength thoracic exercises for use in athletes.

DESIGN

Systematic review involving expert reviewers at key stages: searches and screening (n=1), eligibility, evaluation, data extraction and evaluation (n=3). Key databases and social media sources were searched to 16 August 2019. Eligible exercises were thoracic exercises to promote mobility, motor control, work capacity and strength. A narrative synthesis enabled an outcome-based classification of exercises, with level of evidence of individual sources informing overall level of evidence for each outcome (Oxford Centre for Evidence-based Medicine).

RESULTS

From 2348 sources (social media, database searches and other sources), 38 exercises were included. Sources included images, video clips and written descriptions of exercises. Exercises targeting all planes of motion were evaluated and classified according to outcome. Exercises comprised functional and non-functional exercises for mobility (n=9), work capacity (n=15), motor control (n=7) and strength (n=7). Overall level of evidence for each outcome was level 5.

CONCLUSION

This synthesis and evaluation of exercises has captured the scope of thoracic exercises used in 'practice'. Evaluation against an expert-derived outcome-based classification provides practitioners with a framework to facilitate exercise prescription. Evaluation of validity and effectiveness of exercises on outcomes is now required.

Vitamins and Minerals for Energy, Fatigue and Cognition: A Narrative Review of the Biochemical and Clinical Evidence

Vitamins and minerals are essential to humans as they play essential roles in a variety of basic metabolic pathways that support fundamental cellular functions. In particular, their involvement in energy-yielding metabolism, DNA synthesis, oxygen transport, and neuronal functions makes them critical for brain and muscular function. These, in turn, translate into effects on cognitive and psychological processes, including mental and physical fatigue. This review is focused on B vitamins (B1, B2, B3, B5, B6, B8, B9 and B12), vitamin C, iron, magnesium and zinc, which have recognized roles in these outcomes. It summarizes the biochemical bases and actions of these micronutrients at both the molecular and cellular levels and connects them with cognitive and psychological symptoms, as well as manifestations of fatigue that may occur when status or supplies of these micronutrients are not adequate.

Trunk and Upper Body Fatigue Adversely Affect Running Economy: A Three-Armed Randomized Controlled Crossover Pilot Trial

Trunk muscle fatigue and its negative relationship with running economy (RE) is frequently recognized by practitioners but lacks evidence-based support. Thus, this three-armed randomized controlled crossover pilot trial (RCT) examined the effects of trunk and upper body fatigue protocols on RE, trunk muscle isometric rate of force production, and lactate response in runners. Seven well-trained runners (2 males and 5 females) randomly underwent control (CON), trunk fatigue (TRK), and upper body fatigue (UPR) protocols on three different lab visits. Both workload-matched fatigue protocols-consisting of 24 min of a circuit weight routine-elicited comparable rates of perceived exertion, heart rate responses, and lactate accumulations. As expected, core muscle strength assessed with isometric testing immediately before and after both fatigue protocols, decreased notably. RE (VO₂/kg bodyweight averaged for 1 min) was determined during a 15 min individual anaerobic threshold (IAT) run at 4, 9 and 14 min. The IAT (13.9 to 15.8 km/h) was determined on lab visit one using an incremental treadmill running protocol to volitional exhaustion. RE differed, although not significantly, between CON and both fatigue protocols by 0.75 (4th min) to 1.5 ml/min/kg (9th and 14th min) bodyweight (Time × Mode Interaction: p = 0.2, n_p² = 0.40) with a moderate to large effect size. Despite no signficance, the largest RE differences were observed between TRK and CON (and underscored by the moderate to large effect size). This preliminary pilot RCT revealed that both UPR and TRK conditions might adversely impact running economy at a high intensity, steady state running pace. Future studies should elucidate if these findings are replicable in large scale trials and, in turn, whether periodized core training can beneficially preserve RE.

Energy system contribution during competitive cross-country skiing

Energy system contribution during cross-country (XC) skiing races is dependent on several factors, including the race duration, track profile, and sub-techniques applied, and their subsequent effects on the use of the upper and lower body. This review provides a scientific synopsis of the interactions of energy system contributions from a physiological, technical, and tactical perspective. On average, the aerobic proportion of the total energy expended during XC skiing competitions is comparable to the values for other sports with similar racing times. However, during both sprint (≤ 1.8 km) and distance races (≥ 10 and 15 km, women and men, respectively) a high aerobic turnover interacts with subsequent periods of very high work rates at ~ 120 to 160% of VO_2peak during the uphill sections of the race. The repeated intensity fluctuations are possible due to the nature of skiing, which involves intermittent downhills where skiers can recover. Thus, the combination of high and sustained aerobic energy turnover and repeated work rates above VO_2peak, interspersed with short recovery periods, distinguishes XC skiing from most other endurance sports. The substantially increased average speed in races over recent decades, frequent competitions in mass starts and sprints, and the greater importance of short periods at high speeds in various sub-techniques, have demanded changes in the physiological, technical, and tactical abilities needed to achieve world-class level within the specific disciplines.