Reduced neuromuscular activity and force generation during prolonged cycling

Muscle Tone, Stiffness, and Elasticity in Elite Female Cyclists after Consecutive Short Competitions

Background

For professional road cyclists, most overload injuries affect the lower limbs. They are mostly represented by contractures or muscle shortening, characterised by a variation of muscular tone, stiffness, and elasticity. This real-life study aimed to assess specific mechanical parameters in top-class female cyclists who participated in 3 races a week. Hypothesis. Muscle tone, stiffness, and elasticity will be affected immediately after competition and at the end of the week due to accumulated fatigue.

Methods

Six professional cyclists were evaluated. This pilot study consisted of a controlled trial and three days of competition, with rest days between them. MyotonPRO was used to measure tone, stiffness, and elasticity in six leg muscles: vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), lateral gastrocnemius (LG), and medial gastrocnemius (MG). Daily basal and pre- and postrace measures were carried through to the 3 races in a week.

Results

The muscular tone of VL, VM, LG, and MG and the stiffness of VL, VM, RF, BF, LG, and MG decreased after races. VL and RF were mostly affected by (p=0.05) and (p=0.009), respectively. Basal elasticity improved over time until the last day.

Conclusions

Muscle tone and stiffness decreased after a very intense and exhausting cycling endurance competition. Basal elasticity improved immediately after the race and continued this trend until the end of the week. More research is needed on changes in mechanical properties in competition and risk prevention of injuries.

Using principal component analysis to investigate pacing strategies in elite international canoe kayak sprint races

The aim of this research was to use principal component analysis (PCA) to investigate the current pacing strategies of elite canoe kayak sprint athletes and to determine if there are differences in pacing patterns between medallists and non-medallists at major international competitions. Velocity data collected using global positioning systems (GPS) from all a-finals of major international competitions in 2016-2017 (including canoe and kayak, single and crew boat, and male and female) were downloaded from the International Canoe Federation's website. Data were normalised by the average velocity within each race and organised by race distance. In total 10, 14 and 16 races were analysed, and they followed all-out, positive, and 'seahorse-shaped' pacing strategies for the 200 m, 500 m, and 1000 m events, respectively. Normalised velocity PC1 (p = 0.039, ES = -0.44) and PC2 scores (p < 0.001, ES = -0.73) for 1000 m races were significantly different between medallists and non-medallists; however, significant differences between PCs were not found between groups in shorter race distances (i.e. 200 m and 500 m). Data collected using GPS provide information that can be used to better prepare athletes for canoe kayak sprint races lasting between 30 s and 240 s in duration.

Changes in pacing variation with increasing race duration in ultra-triathlon races

Despite the increasing scientific interest in the relationship between pacing and performance in endurance sports, little information is available about pacing and pacing variation in ultra-endurance events such as ultra-triathlons. Therefore, we aimed to investigate the trends of pacing, pacing variation, the influence of age, sex, and performance level in ultra-triathlons of different distances. We analysed 969 finishers (849 men, 120 women) in 46 ultra-triathlons longer than the original Ironman® distance (e.g., Double-, Triple-, Quintuple- and Deca Iron ultra-triathlons) held from 2004 to 2015. Pacing speed was calculated for every cycling and running lap. Pacing variation was calculated as the coefficient of variation (%) between the average speed of each lap. Performance level (i.e., fast, moderate, slow) was defined according to the 33.3 and 66.6 percentile of the overall race time. A multivariate analysis (two-way ANOVA) was applied for the overall race time as the dependent variable with 'sex' and 'age group' as independent factors. Another multivariate model with 'age' and 'sex' as covariates (two-way ANCOVA) was applied with pacing variation (cycling and running) as the dependent variable with 'race' and 'performance level' as independent factors. Different pacing patterns were observed by event and performance level. The general pacing strategy applied was a positive pacing. In Double and Triple Iron ultra-triathlon, faster athletes paced more evenly with less variation than moderate or slower athletes. The variation in pacing speed increased with the length of the race. There was no significant difference in pacing variation between faster, moderate, and slower athletes in Quintuple and Deca Iron ultra-triathlon. Women had a slower overall performance than men. The best overall times were achieved at the age of 30-39 years. Successful ultra-triathlon athletes adapted a positive pacing strategy in all race distances. The variation in pacing speed increased with the length of the race. In shorter ultra-triathlon distances (i.e., Double and Triple Iron ultra-triathlon), faster athletes paced more evenly with less variation than moderate or slower athletes. In longer ultra-triathlon distances (i.e., Quintuple and Deca Iron ultra-triathlon), there was no significant difference in pacing variation between faster, moderate, and slower athletes.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

What Is the Evidence That Dietary Macronutrient Composition Influences Exercise Performance? A Narrative Review

The introduction of the needle muscle biopsy technique in the 1960s allowed muscle tissue to be sampled from exercising humans for the first time. The finding that muscle glycogen content reached low levels at exhaustion suggested that the metabolic cause of fatigue during prolonged exercise had been discovered. A special pre-exercise diet that maximized pre-exercise muscle glycogen storage also increased time to fatigue during prolonged exercise. The logical conclusion was that the athlete's pre-exercise muscle glycogen content is the single most important acutely modifiable determinant of endurance capacity. Muscle biochemists proposed that skeletal muscle has an obligatory dependence on high rates of muscle glycogen/carbohydrate oxidation, especially during high intensity or prolonged exercise. Without this obligatory carbohydrate oxidation from muscle glycogen, optimum muscle metabolism cannot be sustained; fatigue develops and exercise performance is impaired. As plausible as this explanation may appear, it has never been proven. Here, I propose an alternate explanation. All the original studies overlooked one crucial finding, specifically that not only were muscle glycogen concentrations low at exhaustion in all trials, but hypoglycemia was also always present. Here, I provide the historical and modern evidence showing that the blood glucose concentration-reflecting the liver glycogen rather than the muscle glycogen content-is the homeostatically-regulated (protected) variable that drives the metabolic response to prolonged exercise. If this is so, nutritional interventions that enhance exercise performance, especially during prolonged exercise, will be those that assist the body in its efforts to maintain the blood glucose concentration within the normal range.

Prefrontal cortex activation during incremental inspiratory loading in healthy participants

We aimed to investigate whether changes in prefrontal cortex (PFC) oxyhemoglobin (O₂Hb) and deoxyhemoglobin (HHb) associates with inspiratory muscle effort during inspiratory threshold loading (ITL) in healthy participants. Participants performed an incremental ITL. Breathing pattern, partial pressure of end-tidal CO₂ (P_ETCO₂), mouth pressure and O₂Hb and HHb over the right dorsolateral PFC, sternocleidomastoid (SCM), and diaphragm/intercostals (Dia/IC) were monitored. Fourteen healthy participants (8 men; 29 ± 5 years) completed testing. Dyspnea was higher post- than pre-ITL (5 ± 1 vs. 0 ± 1, respectively; P<0.05). PFC O₂Hb increased (P < 0.001) and HHb decreased (P = 0.001) at low loads but remained stable with increasing ITL intensities. PFC total hemoglobin increased at task failure compared to rest. SCM HHb increased throughout increasing intensities. SCM and Dia/IC total hemoglobin increased in the at task failure compared to rest. P_ETCO₂ did not change (P = 0.528). PFC is activated early during the ITL but does not show central fatigue at task failure despite greater dyspnea and an imbalance of SCM oxygen demand and delivery.

Pacing strategies and relationships between speed and stroke parameters for elite sprint kayakers in single boats

The study aimed to determine the pacing strategies of elite single-boat sprint kayakers, as well as the relationships between stroke parameters (stroke rate (SR) and stroke length (SL)) and kayak speed throughout the race. High-resolution split speed and stroke parameter data from men's (MK1) and women's (WK1) single-boat A- and B-finals in 2016-2017 international sprint kayak competitions were analysed. Correlation coefficients were calculated between SR-speed and SL-speed during each split for each race group. Athletes followed all-out, positive and seahorse-shaped pacing strategies for the 200 m, 500 m and 1000 m races, respectively. SL-speed had greater correlations during the first half of the MK1 200 m race, whereas SR-speed had greater correlations during the second half. SR-speed correlations were greater than SL-speed correlations throughout the final 150 m of WK1 200 m races. There were large and very large correlations between SR-speed at the end of both the WK1 500 m and MK1 1000 m race distances, respectively, despite following different pacing strategies. Single-boat pacing strategies change due to race distance during major international sprint kayak competitions, whereas the relationships between stroke parameters and speed change depending on athlete sex and the race distance.

The placebo effect in breath holding: a preliminary behavioral investigation

PURPOSE

This study seeks to evaluate effects of expectations and conditioning on dry breath holding.

METHODS

Sixty healthy volunteers were subdivided into 3 groups and were tested across 4 breath holding trials. Participants of the Control group (C) did not undergo any manipulation. Participants of the placebo (P) and nocebo (N) groups were told that they would inhale O2 (actually sham O2) or CO2 (actually sham CO2) along with opposite information that this would enhance or worsen their breath holding time, respectively. Opposite conditioning paradigms based on false visual feedback were employed to reinforce participants' positive (placebo) and negative (nocebo) beliefs.

RESULTS

The P group showed the greater increase in breath holding time from baseline to the last trial (p = 0.0001) and the longest breath holding time in the last trial compared to the C group (p = 0.02) and the N group (p = 0.0001). Additionally, in the last trial the P group showed a greater decrease in peripheral oxygen saturation (SpO2) as compared to the C group (p = 0.04) and the N group (p = 0.001). Heart rate (HR) was accelerated in the N group during breath holding (in comparison to the P group [p = 0.04] and C group [p = 0.04]).

CONCLUSIONS

Psychological components can affect behavioral and physiological parameters in breath holding. This study may inform future research about the role of placebo and nocebo effects for conditions in which critical functions are at play.

Pacing, Exercise Intensity, and Technique by Performance Level in Long-Distance Cross-Country Skiing

Introduction

Long-distance cross-country skiing (XCS) has gained increased popularity within the past decades. However, research about long-distance XCS is limited; therefore, the aim of this study was to analyze the intensity distribution, technique application, and pacing strategies during long-distance XCS racing.

Methods

Heart rate (HR) and section skiing speeds of 9 elite (ranked 1–100) and 10 amateur skiers (ranked 101–1,500) during the 90-km Vasaloppet race were collected. In addition, during the first uphill, the first 1,000 skiers were video-recorded to analyze the applied skiing strategy (e.g. grip-waxed skis versus exclusive double poling).

Results

Mean race intensity was 82% of maximal HR and was not different between performance groups even though elite skiers skied ∼15% faster than amateurs. There was an interaction effect of section × group with a pronounced decrease in HR in amateurs compared with more even pacing in elite skiers (0.13 vs. 0.04% decrease/km) and skiing at higher percentage in the high-intensity zones in elite compared with amateurs (46 vs. 24%). Ninety-eight percent of the top 100 skiers and 59% of the first 1,000 skiers used exclusively double poling.

Conclusion

Elite and amateur skiers ski at comparable mean race exercise intensity, but they have clear differences in skiing speed. The difference in the pacing profiles between elite and amateur skiers (more even vs. distinct positive pacing) demonstrate the greater capacity of the former with respect to physiological capacity and highlights that amateurs seem to start too fast according to their capacities. The exclusive application of the double poling technique is no longer a phenomenon of elite skiers but is widely used among the top 1,000 ranked skiers.

Effects of periodic carbohydrate ingestion on endurance and cognitive performances during a 40-km cycling time-trial under normobaric hypoxia in well-trained triathletes

The purpose of this study was to examine CHO ingestion on a cognitive task using a field-simulated time-trial (TT) under hypoxia in well-trained triathletes. Ten male triathletes (age: 22.1 ± 1.1 years; VO₂max: 59.4 ± 1.4 ml/kg/min) participated in this double-blind/crossover/counter-balanced design study. Participants completed 3 TT trials: 1) normoxic placebo (NPLA; FiO₂ = 20.9%), 2) hypoxic placebo (HPLA; FiO₂ = 16.3%), and 3) hypoxic CHO (HCHO; 6% CHO provided as 2 ml/kg/15 min; FiO₂ = 16.3%). During the TT, physiological responses (SpO₂, HR, RPE, and blood glucose/lactate), cognitive performance, and cerebral haemodynamics were measured. Hypoxia reduced TT performance by ~3.5-4% (p < 0.05), but CHO did not affect TT performance under hypoxia. For the cognitive task, CHO slightly preserved exercise-induced cognitive reaction speed but did not affect response accuracy during hypoxic exercise. However, CHO did not preserve the decreased Hb-Diff (cerebral blood flow, CBF) and increased HHb in the prefrontal lobe (p < 0.05) during hypoxic exercise, and CHO failed to preserve hypoxia-suppressed prefrontal CBF and tissue oxygen saturation. In conclusion, the present study demonstrates that CHO is effective in sustaining reaction speed for a cognitive task but not promoting TT performance during hypoxic exercise, which would be important for strategy-/decision-making when athletes compete at moderate high-altitude.

Towards a three-dimensional framework of centrally regulated and goal-directed exercise behaviour: a narrative review

The Central Governor Model (CGM) ignited a paradigm shift from concepts of catastrophic failure towards central regulation of exercise performance. However, the CGM has focused on the central integration of afferent feedback in homeostatic control. Accordingly, it neglected the important role of volitional self-regulatory control and the integration of affective components inherently attached to all physiological cues. Another limitation is the large reliance on the Gestalt phenomenon of perceived exertion. Thus, progress towards a comprehensive multidimensional model of perceived fatigability and exercise regulation is needed. Drawing on Gate Control Theory of pain, we propose a three-dimensional framework of centrally regulated and goal-directed exercise behaviour, which differentiates between sensory, affective and cognitive processes shaping the perceptual milieu during exercise. We propose that: (A) perceived mental strain and perceived physical strain are primary determinants of pacing behaviour reflecting sensory-discriminatory processes necessary to align planned behaviour with current physiological state, (B) core affect plays a primary and mediatory role in exercise and performance regulation, and its underlying two dimensions hedonicity and arousal reflect affective-motivational processes triggering approach and avoidance behaviour, and (C) the mindset-shift associated with an action crisis plays a primary role in volitional self-regulatory control reflecting cognitive-evaluative processes between further goal-pursuit and goal-disengagement. The proposed framework has the potential to enrich theory development in centrally regulated and goal-directed exercise behaviour by emphasising the multidimensional dynamic processes underpinning perceived fatigability and provides a practical outline for investigating the complex interplay between the psychophysiological determinants of pacing and performance during prolonged endurance exercise.

Placebo response in pain, fatigue, and performance: Possible implications for neuromuscular disorders

The placebo response in neuromuscular disorders is not well understood. The only available data regarding its underlying mechanisms are related to neuropathic pain. In this review, we describe the factors that contribute to improved outcomes in the placebo arm, with specific attention to pain and fatigue, as well as some of the most important psychobiological mechanisms that may explain such a response. This approach may also improve our insight into the symptomatology and therapeutic responses of other neuromuscular disorders. The fact that >90% of tested analgesics for neuropathic pain have failed in advanced phases of clinical trials should prompt a greater investment of effort and resources into understanding the mechanisms and impact of placebos in clinical research. Such an endeavor will help improve the design of clinical trials and will provide information that informs clinical neuromuscular practice. Muscle Nerve 56: 358-367, 2017.

Effects of reduced-volume of sprint interval training and the time course of physiological and performance adaptations

This study sought to determine the time course of training adaptations to two different sprint interval training programmes with the same sprint: rest ratio (1:8) but different sprint duration. Nine participants (M: 7; F: 2) were assigned to 15-second training group (15TG) consisting of 4-6 × 15-second sprints interspersed with 2-minute recovery, whereas eight participants (M: 5; F: 3) were assigned to 30-second training group (30TG) consisting of 4-6 × 30 second sprints interspersed with 4-minute recovery. Both groups performed their respective training twice per week over 9 weeks and changes in peak oxygen uptake (V˙O2peak) and time to exhaustion (TTE) were assessed every 3 weeks. Additional eight healthy active adults (M: 6; F: 2) completed the performance assessments 9 weeks apart without performing training (control group, CON). Following 9 weeks of training, both groups improved V˙O2peak (15TG: 12.1%; 30TG: 12.8%, P<.05) and TTE (15TG: 16.2%; 30TG: 12.8%, P<.01) to a similar extent. However, while both groups showed the greatest gains in V˙O2peak at 3 weeks (15TG: 16.6%; 30TG: 17.0%, P<.001), those in TTE were greatest at 9 weeks. CON did not change any of performance variables following 9 weeks. This study demonstrated that while the changes in cardiorespiratory function plateau within several weeks with sprint interval training, endurance capacity (TTE) is more sensitive to such training over a longer time frame in moderately-trained individuals. Furthermore, a 50% reduction in sprint duration does not diminish overall training adaptations over 9 weeks.

Similarities and Differences in Pacing Patterns in a 161-km and 101-km Ultra-Distance Road Race

Tan, PLS, Tan, FHY, and Bosch, AN. Similarities and differences in pacing patterns in a 161-km and 101-km ultra-distance road race. J Strength Cond Res 30(8): 2145-2155, 2016-The purpose of this study was to establish and compare the pacing patterns of fast and slow finishers in a tropical ultra-marathon. Data were collected from the Craze Ultra-marathon held on the 22nd and 21st of September in 2012 and 2013, respectively. Finishers of the 161-km (N = 47) and 101-km (N = 120) categories of the race were divided into thirds (groups A-C) by merit of finishing time. Altogether, 17 and 11 split times were recorded for the 161-km and 101-km finishers, respectively, and used to calculate the mean running speed for each distance segment. Running speed for the first segment was normalized to 100, with all subsequent splits adjusted accordingly. Running speed during the last 5 km was calculated against the mean race pace to establish the existence of an end spurt. A reverse J-shaped pacing profile was demonstrated in all groups for both distance categories and only 38% of the finishers executed an end spurt. In the 101-km category, in comparison with groups B and C, group A maintained a significantly more even pace (p = 0.013 and 0.001, respectively) and completed the race at a significantly higher percent of initial starting speed (p = 0.001 and 0.001, respectively). Descriptive data also revealed that the top 5 finishers displayed a "herd-behavior" by staying close to the lead runner in the initial portion of the race. These findings demonstrate that to achieve a more even pace, recreational ultra-runners should adopt a patient sustainable starting speed, with less competitive runners setting realistic performance goals whereas competitive runners with a specific time goal to consider running in packs of similar pace.

Re-Evaluation of Old Findings on Stroke Volume Responses to Exercise and Recovery by Nitrous-Oxide Rebreathin

It is important to verify the old findings of Cumming (1972) and Goldberg and Shephard (1980) who showed that stroke volume (SV) may be higher during recovery rather than during exercise, in order to organize the number of intervals throughout training sessions. The purpose of this study was to re-evaluate individual SV responses to various upright cycling exercises using the nitrous-oxide rebreathing method. Nine moderate to well-trained male athletes volunteered to take part in the study (maximal O₂ uptake (VO_2max): 60.2 ± 7 mL⋅min^-1⋅kg^-1). Workloads ranging from 40-100% of VO_2max were applied to determine individual peak SV (SV_peak) response. Results showed that SV responses were higher during exercise compared to recovery in all exercise loads from 40-100% of VO_2max. Mean SV responses to individual SVpeak loads were also higher during exercise compared to recovery (122.9 ± 2.5 versus 105.3 ± 5.93 mL). The highest SV responses to 10 min exercises of 40-70% of VO_2max were obtained in the 5^th or 7.5^th min of each stage (p≤0.05). Meanwhile, during 5 min exercises between 80-100% of VO_2max, peak SV responses were observed in the 3^rd min of loading (p≤0.05). In conclusion, individual SVpeak levels encountered over wide exercise intensity ranges showed that SVpeak development may also be correlated to exercise intensity corresponding to individual SV_peak loads.

Electromyographical and Perceptual Responses to Different Resistance Intensities in a Squat Protocol: Does Performing Sets to Failure With Light Loads Produce the Same Activity?

This investigation examined peak motor unit activity during sets that differed in resistance (50, 70, or 90% 1 repetition maximum [1RM]). Ten resistance-trained men (age, 23 ± 3 years; height, 187 ± 7 cm; body mass, 91.5 ± 6.9 kg; squat 1RM, 141 ± 28 kg) were assessed by electromyography (EMG) on the vastus lateralis and vastus medialis muscles in a randomized within-subject experiment consisting of 2 test visits: a drop-set day and a single-set day using only the 50% of 1RM intensity performed to failure. At the start of each day, subjects performed 2 submaximal repetition sets (50% 1RM × 10 repetitions and 70% 1RM × 7 repetitions). On the drop-set day, subjects performed 3 consecutive maximal repetition sets at 90%, 70%, and 50% 1RM to failure with no rest periods in between. On the single-set day, subjects performed a maximal repetition set at 50% 1RM to failure. Overall, the maximal repetition sets to failure at 50% and 70% 1RM resulted in higher peak EMG amplitude than during submaximal repetition sets with the same resistance. However, peak EMG amplitude was significantly (p ≤ 0.05) greater in the maximal 90% 1RM set than all other sets performed. When sets were performed to failure, ratings of perceived exertion (CR-10) did not differ over the intensity range of loads and suggests that perception is not capable of accurately detecting the actual amount of motor unit activation. The results of this investigation indicate that using higher external resistance is a more effective means of increasing motor unit activity than increasing the number of repetitions performed with lighter weights even when the end point is muscular failure. Accordingly, previous recommendations for the use of heavier loads during resistance training programs to stimulate the maximal development of strength and hypertrophy are further supported.

Role of carbohydrate in central fatigue: a systematic review

Carbohydrate (CHO) depletion is linked to neuromuscular fatigue during exercise. While its role at peripheral level is relatively well understood, less is known about its impact centrally. The aim of this systematic review was to critically analyze the effects of CHO on central fatigue (CF) assessed by various neurophysiological techniques. Four databases were searched using PRISMA guidelines through February 2016. The inclusion criteria were: CHO as intervention against a placebo control, fatigue induced by prolonged exercise and assessed using neurophysiological measures [voluntary activation (VA), superimposed twitch (SIT), M-wave, electromyography], alongside maximal voluntary contraction (MVC). Seven papers were reviewed, where exercise duration lasted between 115 and 180 min. CHO improved exercise performance in three studies, whereby two of them attributed it to CF via attenuation of VA and SIT reductions, while the other indicated peripheral involvement via attenuation of M-wave reduction. Although a few studies suggest that CHO attenuates CF, data on its direct effects on neurophysiological outcome measures are limited and mixed. Generally, measures employed in these studies were inadequate to conclude central contribution to fatigue. Factors including the techniques used and the lack of controls render additional confounding factors to make definitive deductions. Future studies should employ consistent techniques and appropriate neurophysiological controls to distinguish CHO effect at central level. The use of pharmacological intervention should be incorporated to elucidate involvement of central mechanisms.

Effect of Deception of Distance on Prolonged Cycling Performance

This study examined the effect of deception of distance end-point on prolonged cycling performance. 21 subjects were randomly allocated to three groups ( n = 7 per group). Each group completed three self-paced time-trials separated by one day. Subjects were told that each trial was a 30-km time-trial and were required to complete the distance in the fastest time possible. Following the initial trial of 30 km, one group completed Trial 2 with a longer distance (long distance group; 36 km), another group with a shorter distance (24 km; short distance group), and the third group as control (30 km; control). Each group then completed a third time-trial of 30 km. At no time was the deception of distance in Trial 2 disclosed to the subjects, and all sources of physiological and mechanical feedback were withheld during the trials. Data from Trials 1 and 3 were analysed by repeated-measures analysis of covariance. Time to complete Trial 1 was similar among groups (–65 min.). Following the deception in Trial 2 the time to complete the 30 km in Trial 3 was increased for the short distance group, decreased for the long distance group, whilst the time for the control group remained unchanged. The times to complete the 30 km on Trials 1 and 3 were matched by changes in power output throughout the trials. It is concluded that subjects deceived of the actual distance completed will complete the subsequent performance trial based on perceived effort rather than on actual distance.

Electromyographic, mechanomyographic, and metabolic responses during cycle ergometry at a constant rating of perceived exertion

Ten subjects performed four 8-min rides (65%-80% peak oxygen consumption) to determine the physical working capacity at the OMNI rating of perceived exertion (RPE) threshold (PWCOMNI). Polynomial regression analyses were used to examine the patterns of responses for surface electromyographic (EMG) amplitude (EMG AMP), EMG mean power frequency (EMG MPF), mechanomyographic (MMG) AMP, and MMG MPF of the vastus lateralis as well as oxygen consumption rate, respiratory exchange ratio (RER), and power output (PO) were examined during a 1-h ride on a cycle ergometer at a constant RPE that corresponded to the PWCOMNI. EMG AMP and MMG MPF tracked the decreases in oxygen consumption rate, RER, and PO, while EMG MPF and MMG AMP tracked RPE. The decreases in EMG AMP and MMG MPF were likely attributable to decreases in motor unit (MU) recruitment and firing rate, while the lack of change in MMG AMP may have resulted from a balance between MU de-recruitment as PO decreased, and an increase in the ability of activated fibers to oscillate. The current findings suggested that during submaximal cycle ergometry at a constant RPE, MU de-recruitment and mechanical changes within the muscle may influence the perception of effort via feedback from group III and IV afferents.

Locomotor muscle fatigue is not critically regulated after prior upper body exercise

This study examined the effects of prior upper body exercise on subsequent high-intensity cycling exercise tolerance and associated changes in neuromuscular function and perceptual responses. Eight men performed three fixed work-rate (85% peak power) cycling tests: 1) to the limit of tolerance (CYC); 2) to the limit of tolerance after prior high-intensity arm-cranking exercise (ARM-CYC); and 3) without prior exercise and for an equal duration as ARM-CYC (ISOTIME). Peripheral fatigue was assessed via changes in potentiated quadriceps twitch force during supramaximal electrical femoral nerve stimulation. Voluntary activation was assessed using twitch interpolation during maximal voluntary contractions. Cycling time during ARM-CYC and ISOTIME (4.33 ± 1.10 min) was 38% shorter than during CYC (7.46 ± 2.79 min) (P < 0.001). Twitch force decreased more after CYC (-38 ± 13%) than ARM-CYC (-26 ± 10%) (P = 0.004) and ISOTIME (-24 ± 10%) (P = 0.003). Voluntary activation was 94 ± 5% at rest and decreased after CYC (89 ± 9%, P = 0.012) and ARM-CYC (91 ± 8%, P = 0.047). Rating of perceived exertion for limb discomfort increased more quickly during cycling in ARM-CYC [1.83 ± 0.46 arbitrary units (AU)/min] than CYC (1.10 ± 0.38 AU/min, P = 0.003) and ISOTIME (1.05 ± 0.43 AU/min, P = 0.002), and this was correlated with the reduced cycling time in ARM-CYC (r = -0.72, P = 0.045). In conclusion, cycling exercise tolerance after prior upper body exercise is potentially mediated by central fatigue and intolerable levels of sensory perception rather than a critical peripheral fatigue limit.

A descriptive comparison of sprint cycling performance and neuromuscular characteristics in able-bodied athletes and paralympic athletes with cerebral palsy

OBJECTIVE

This study investigated the sprint cycling performance and neuromuscular characteristics of Paralympic athletes with cerebral palsy (CP) during a fatiguing maximal cycling trial compared with those of able-bodied (AB) athletes.

DESIGN

Five elite athletes with CP and 16 AB age- and performance-matched controls performed a 30-sec Wingate cycle test. Power output (W/kg) and fatigue index (%) were calculated. Electromyography was measured in five bilateral muscles and expressed in mean amplitude (mV) and median frequency (Hz).

RESULTS

Power output was significantly higher in the AB group (10.4 [0.5] W/kg) than in the CP group (9.8 [0.5] W/kg) (P < 0.05). Fatigue index was statistically similar between the AB (27% [0.1%]) and CP (25% [0.1%]) groups. Electromyographic mean amplitude and frequency changed similarly in all muscle groups tested, in both affected and nonaffected sides, in the CP and AB groups (P < 0.05). Neuromuscular irregularities were identified in the CP group.

CONCLUSIONS

The similarity in fatigue between the CP and AB groups indicates that elite athletes with CP may have a different exercise response to others with CP. The authors propose that this may result from high-level training over many years. This has rehabilitative implications, as it indicates near-maximal adaptation of the CP body toward normal levels.

Exercise Intensity and Pacing Strategy of Cross-country Skiers during a 10 km Skating Simulated Race

The aim of this study was to observe the cardiovascular demands by monitoring the heart rate (HR) and the pacing strategy by evaluating the speed during a simulated cross-country skiing race. Eleven skiers (16.45 ± 1.67 yrs; 21.32 ± 2.03 kg m(-2); 72.35 ± 4.69 mL min(-1) kg(-1)) competed in a 10 km event divided into four laps. The HR profile was classified into four intensity zones. The skiers spent 66.84 ± 23.64% and 31.82 ± 23.77% of the total time above 90% and at 80-90% of the HRmax respectively, whereas the lower zones were negligible. During the event, a progressive increase in intensity was observed: HRmean raised by 2.42% in the last versus the first lap (p < 0.001). The skiers decreased their speed in the second (p = 0.017) and the third laps (p < 0.001) compared to with the first lap. In the fourth lap the skiers increased the speed slightly but without statistical difference. The speed maintained by the skiers resulted in the adoption of a reverse J-shaped pacing strategy.

Pacing strategies during the swim, cycle and run disciplines of sprint, Olympic and half-Ironman triathlons

PURPOSE

This study investigated the influence of distance on self-selected pacing during the swim, cycle and run disciplines of sprint, Olympic and half-Ironman (HIM) distance triathlon races.

METHOD

Eight trained male triathletes performed the three individual races in <2 months. Participants' bikes were fitted with Schoberer Rad Meßtechnik to monitor speed, power output and heart rate during the cycle discipline. Global positioning system was worn to determine speed and heart rate during the swim and run disciplines.

RESULT

An even swim pacing strategy was adopted across all distances. A more stochastic pacing was observed during the HIM cycle [standard deviation of exposure variation analysis (EVASD) = 3.21 ± 0.61] when compared with the sprint cycle discipline (EVASD = 3.84 ± 0.44, p = 0.018). Only 20.9 ± 4.1 % of the cycling time was spent more than 10 % above the mean power output in the HIM, compared with 43.8 ± 2.9 % (p = 0.002) and 37.7 ± 11.1 % (p = 0.039) during the sprint and Olympic distance triathlons, respectively. Conversely, 13.6 ± 5.1 % of the cycling time was spent 5-10 % below the mean power output during the HIM, compared with 5.9 ± 1.2 % (p = 0.034) and 8.0 ± 5.1 % (p = 0.045) during the sprint and Olympic distance triathlons, respectively. A negative pacing strategy was adopted during the sprint distance run, compared with positive pacing strategy during the Olympic and HIM.

CONCLUSION

Results of this study suggest that pacing strategies during triathlon are highly influenced by distance and discipline, and highlight the importance of developing pacing strategies based on distance, strengths and individual fitness.

Shorter intervals at peak SV vs.V̇O2max may yield high SV with less physiological stress

The purpose of this study was to evaluate whether greater and sustainable stroke volume (SV) responses may be obtained by exercise intensities corresponding to peak SV (SVpeak) vs. maximal O2 consumption (VO2max), and short vs. long intervals (SI vs. LI). Nine moderate- to well-trained male athletes competing at regional level specialists of cyclist, track and field volunteered to take part in the study (VO2max: 59.7 ± 7.4 mL·min(-1)·kg(-1)). Following familiarisation sessions, VO2max was determined, and then SVpeak was evaluated using exercise intensities at 40%-100% of VO2max by nitrous-oxide rebreathing (N2ORB) method. Then each separate participant exercised wattages corresponding to individual VO2max and SVpeak during both SI (SIVO2max and SI(SVpeak)) and LI (LIVO2max and LI(SVpeak)) workouts on a cycle ergometer. Main results showed that both SIVO2max and SI(SVpeak) yielded greater SV responses than LIVO2max and LI(SVpeak) (p ≤ 0.05). Mean SV responses were greater in LI(SVpeak) than in LIVO2max (p ≤ 0.05), but there was no statistical difference between SI(SVpeak) and SIVO2max. However, there was significantly less physiological stress based on VO2, respiratory exchange ratio, heart rate and rate of perceived exhaustion in SVpeak than in [Formula: see text] intensities (p ≤ 0.05). Moreover, SV responses at exercise phases increased in the early stages and remain stable until the end of SIVO2max and SI(SVpeak) workouts (p > 0.05), while they were gradually decreasing in LIVO2max and LI(SVpeak) sessions (p ≤ 0.05). In conclusion, if the aim of a training session is to improve SVpeak with less physiological stress, SI(SVpeak) seems a better alternative than other modalities tested in the present study.

Factors influencing pacing in triathlon

Triathlon is a multisport event consisting of sequential swim, cycle, and run disciplines performed over a variety of distances. This complex and unique sport requires athletes to appropriately distribute their speed or energy expenditure (ie, pacing) within each discipline as well as over the entire event. As with most physical activity, the regulation of pacing in triathlon may be influenced by a multitude of intrinsic and extrinsic factors. The majority of current research focuses mainly on the Olympic distance, whilst much less literature is available on other triathlon distances such as the sprint, half-Ironman, and Ironman distances. Furthermore, little is understood regarding the specific physiological, environmental, and interdisciplinary effects on pacing. Therefore, this article discusses the pacing strategies observed in triathlon across different distances, and elucidates the possible factors influencing pacing within the three specific disciplines of a triathlon.

Physiological and psychological effects of deception on pacing strategy and performance: a review

The aim of an optimal pacing strategy during exercise is to enhance performance whilst ensuring physiological limits are not surpassed, which has been shown to result in a metabolic reserve at the end of the exercise. There has been debate surrounding the theoretical models that have been proposed to explain how pace is regulated, with more recent research investigating a central control of exercise regulation. Deception has recently emerged as a common, practical approach to manipulate key variables during exercise. There are a number of ways in which deception interventions have been designed, each intending to gain particular insights into pacing behaviour and performance. Deception methodologies can be conceptualised according to a number of dimensions such as deception timing (prior to or during exercise), presentation frequency (blind, discontinuous or continuous) and type of deception (performance, biofeedback or environmental feedback). However, research evidence on the effects of deception has been perplexing and the use of complex designs and varied methodologies makes it difficult to draw any definitive conclusions about how pacing strategy and performance are affected by deception. This review examines existing research in the area of deception and pacing strategies, and provides a critical appraisal of the different methodological approaches used to date. It is hoped that this analysis will inform the direction and methodology of future investigations in this area by addressing the mechanisms through which deception impacts upon performance and by elucidating the potential application of deception techniques in training and competitive settings.

Muscle fatigue based evaluation of bicycle design

Bicycling posture leads to considerable discomfort and a variety of chronic injuries. This necessitates a proper bicycle design to avoid injuries and thereby enhance rider comfort. The objective of this study was to investigate the muscle activity during cycling on three different bicycle designs, i.e., rigid frame (RF), suspension (SU) and sports (SP) using surface electromyography (sEMG). Twelve male volunteers participated in this study. sEMG signals were acquired bilaterally from extensor carpi radialis (ECR), trapezius medial (TM), latissimus dorsi medial (LDM) and erector spinae (ES), during 30 min of cycling on each bicycle and after cycling. Time domain (RMS) and frequency domain (MPF) parameters were extracted from acquired sEMG signals. From the sEMG study, it was found that the fatigue in right LDM and ES were significantly (p < 0.05) higher in SP bicycle. This was corroborated by a psychophysical assessment based on RBG pain scale. The study also showed that there was a significantly lesser fatigue with the SU bicycle than the RF and SP bicycles.

Is recovery driven by central or peripheral factors? A role for the brain in recovery following intermittent-sprint exercise

Prolonged intermittent-sprint exercise (i.e., team sports) induce disturbances in skeletal muscle structure and function that are associated with reduced contractile function, a cascade of inflammatory responses, perceptual soreness, and a delayed return to optimal physical performance. In this context, recovery from exercise-induced fatigue is traditionally treated from a peripheral viewpoint, with the regeneration of muscle physiology and other peripheral factors the target of recovery strategies. The direction of this research narrative on post-exercise recovery differs to the increasing emphasis on the complex interaction between both central and peripheral factors regulating exercise intensity during exercise performance. Given the role of the central nervous system (CNS) in motor-unit recruitment during exercise, it too may have an integral role in post-exercise recovery. Indeed, this hypothesis is indirectly supported by an apparent disconnect in time-course changes in physiological and biochemical markers resultant from exercise and the ensuing recovery of exercise performance. Equally, improvements in perceptual recovery, even withstanding the physiological state of recovery, may interact with both feed-forward/feed-back mechanisms to influence subsequent efforts. Considering the research interest afforded to recovery methodologies designed to hasten the return of homeostasis within the muscle, the limited focus on contributors to post-exercise recovery from CNS origins is somewhat surprising. Based on this context, the current review aims to outline the potential contributions of the brain to performance recovery after strenuous exercise.

The effects of placebos and nocebos on physical performance

In this chapter we present and discuss recent studies on the mechanisms underlying placebo and nocebo effects in physical performance, showing how expectations and both pharmacological and nonpharmacological preconditioning procedures can be very effective in inducing placebo responses, with important implications for sport competitions. Furthermore, we place these findings within the biological model of central governor of fatigue, whose main goal is to protect our body from damage. A crucial aspect of this emerging field of placebo studies is related to the limit beyond which these procedures can be called doping in all respects.

Efeito da dieta hiperlipídica e do treinamento aeróbico na aterosclerose em camundongos apoE-/-

INTRODUÇÃO: A população brasileira tem seguido a tendência dos países desenvolvidos, cuja característica é o aumento do consumo de gorduras e sedentarismo. OBJETIVO: Investigar os efeitos da dieta hiperlipídica e do treinamento sobre o peso corporal, o consumo alimentar, a massa corporal magra, os lipídios plasmáticos, o peso do fígado e a aterosclerose em camundongos com deficiência de apolipoproteína E (apoE-/-). MÉTODOS: vinte e seis camundongos foram divididos em grupos/dieta: NS (normolipídica e sedentário), HS (hiperlipídica e sedentário), NT (normolipídica e treinamento) e HT (hiperlipídica e treinamento). Aferiu-se peso corporal (PC), consumo alimentar (CA) e peso relativo do fígado (PRF). Calculou-se a água da carcaça (A%) pela diferença do peso pré e pós-secagem, gordura (G%) por Soxhlet e proteína (P%) por Kjeldahl. Determinaram-se colesterol total (CT), triglicerídeos (TG) e HDL por método enzimático-colorimétrico e LDL e VLDL pela formula de Friedewald. Analisou-se a aterosclerose por fotomicrografia. Utilizou-se ANOVA e o método de Duncan, com P < 0,05. RESULTADOS: No PC inicial e final, não houve diferença de G% e P% entre os grupos (P > 0,05). A dieta hiperlipídica aumentou o CA (365,3 ± 5,09 vs. 340,16 ± 6,32) e LDL (452,20 ± 114,63 vs. 329,60 ± 77,54) nos animais sedentários e o CT (858,75 ± 140,84 vs. 320,87 ± 157,81) e o LDL (839,36±139,94 vs. 282,66±166,92) nos treinados (P < 0,05). Já o treinamento aumentou o CA (350,4 ± 7,81 vs. 340,16 ± 6,32) e A% (64,23 ± 2,46 vs. 62,62 ± 1,47) nos camundongos normolipídicos e diminuiu o CA (336,68 ± 6,23 vs. 365,3 ± 5,09), TG (22,75 ± 12,36 vs. 66,00 ± 21,88), HDL (14,83 ± 3,95 vs. 37,60 ± 13,12), VLDL (4,55 ± 2,47 vs. 13,20 ± 4,37) e aterosclerose (0,35 ± 0,13 vs. 0,56 ± 0,12) nos hiperlipídicos (P < 0,05). CONCLUSÃO: A dieta hiperlipídica pode desencadear distúrbios no metabolismo lipídico e, com isso, desencadear doenças cardiovasculares; porém, associada ao treinamento, pode diminuir a aterosclerose.

Distribution of Power Output When Establishing a Breakaway in Cycling

A number of laboratory-based performance tests have been designed to mimic the dynamic and stochastic nature of road cycling. However, the distribution of power output and thus physical demands of high-intensity surges performed to establish a breakaway during actual competitive road cycling are unclear. Review of data from professional road-cycling events has indicated that numerous short-duration (5–15 s), high-intensity (~9.5–14 W/kg) surges are typically observed in the 5–10 min before athletes’ establishing a breakaway (ie, riding away from a group of cyclists). After this initial high-intensity effort, power output declined but remained high (~450–500 W) for a further 30 s to 5 min, depending on race dynamics (ie, the response of the chase group). Due to the significant influence competitors have on pacing strategies, it is difficult for laboratory-based performance tests to precisely replicate this aspect of mass-start competitive road cycling. Further research examining the distribution of power output during competitive road racing is needed to refine laboratory-based simulated stochastic performance trials and better understand the factors important to the success of a breakaway.

Análise da técnica de pedalada durante o ciclismo até a exaustão

O objetivo deste estudo foi verificar a influência da fadiga na técnica de pedalada durante teste de ciclismo máximo até a exaustão. Oito ciclistas treinados realizaram um teste incremental máximo e um teste de carga constante até a exaustão com 48 horas de intervalo. As forças resultante (FR) e efetiva (FE) aplicadas no pedal foram calculadas para a determinação do índice de efetividade (IE). A FE apresentou aumento entre o início e fim do teste (de 125 ± 16 para 169 ± 52 N, p=0,03), enquanto o IE e a FR não apresentaram alterações (de 0,55 ± 0,10 para 0,59 ± 0,08, p=0,14; de 230 ± 33 para 284 ± 72 N, p=0,08, respectivamente). O tornozelo apresentou aumento na amplitude de movimento (de 19º ± 4,69 para 28 ± 7,29º, p<0,01). Os resultados sugerem que, durante teste de carga constante até a exaustão, ciclistas treinados mantêm a técnica de pedalada e que esta pode ser uma estratégia para manter a potência.

Changes of whole-body power, muscle function, and jump performance with prolonged cycling to exhaustion

PURPOSE

To quantify how whole-body power, muscle-function, and jump-performance measures change during prolonged cycling and recovery and determine whether there are relationships between the different fatigue measures.

METHODS

Ten competitive or recreationally active male cyclists underwent repeated 20-min stages of prolonged cycling at 70% VO2peak until exhaustion. Whole-body peak power output (PPO) was assessed using an all-out 30-s sprint 17 min into each cycle stage. Ratings of perceived exertion (RPE) were recorded throughout. Isometric and isokinetic muscle-function tests were made between cycle stages, over ~6 min, and during 30-min recovery. Drop-jump measures were tested at exhaustion and during recovery.

RESULTS

PPO initially increased or was maintained in some subjects but fell to 81% of maximum at exhaustion. RPE was near maximal (18.7) at exhaustion, with the time to exhaustion related to the rate of rise of RPE. PPO first started to decline only when RPE exceeded 16 (ie, hard). Peak isometric and concentric isokinetic torque (180°/s) for the quadriceps fell to 86% and 83% of pretest at exhaustion, respectively. In contrast, the peak concentric isokinetic torque (180°/s) of the hamstrings increased by 10% before declining to 93% of maximum. Jump height fell to 92% of pretest at exhaustion and was correlated with the decline in PPO (r = .79). Muscle-function and jump-performance measures did not recover over the 30-min postexercise rest period.

CONCLUSIONS

At exhaustion, whole-body power, muscle-function, and jump-performance measures had all fallen by 7-19%. PPO and drop-jump decrements were linearly correlated and are appropriate measures of maximal performance.

Muscle coordination during an outdoor cycling time trial

INTRODUCTION/PURPOSE

Muscle activity in cycling has primarily been studied in the laboratory; however, conclusions are limited by the ability to recreate realistic environmental conditions. The purpose of this study was to determine muscle coordination patterns in an outdoor time trial and investigate their relationships to power output (PO), total muscle activity (Itot), overall mechanical efficiency (ηO), cadence, and gradient.

METHODS

Surface EMG, gradient, and cycling parameters were measured while cycling 18.8 km outdoors. A principal component analysis was used to establish coordination patterns that were compared with Itot, ηO, PO, cadence, and gradient.

RESULTS

PO was positively correlated with Itot, and high PO was associated with elevated rectus femoris and vastus lateralis activity and synchronization of muscles crossing the same joint. PO and cadence demonstrated positive and negative relationships, respectively, with gradient. Relationships between muscle coordination, PO, ηO, Itot, and gradient showed that muscle coordination, PO, and ηO fluctuate during an outdoor time trial as a result of pacing and gradient. A trade-off existed between ηO and PO, and ηO was dependent on muscle activation around the top and bottom of the pedal cycle and activity in more than the knee extensor muscles. Fluctuations in muscle activity due to the changing PO, from pacing and terrain, seemed to mitigate fatigue indices seen in indoor cycling studies.

CONCLUSIONS

This study provides evidence that muscle activity is dependent on the terrain aspects of the cycle course as muscle coordination changes with the altered locomotor demands. The coordination patterns significantly covaried with PO, Itot, ηO, cadence, and gradient, which highlights the importance of recording these parameters under field conditions and/or careful reproduction of outdoor environments in indoor studies.

Intermittent-sprint performance and muscle glycogen after 30 h of sleep deprivation

PURPOSE

The aim of this study was to determine the effects of 30 h of sleep deprivation on consecutive-day intermittent-sprint performance and muscle glycogen content.

METHODS

Ten male, team-sport athletes performed a single-day "baseline" session and two consecutive-day experimental trials separated either by a normal night's sleep (CONT1 and CONT2) or no sleep (SDEP1 and SDEP2). Each session included a 30-min graded exercise run and 50-min intermittent-sprint exercise protocol, including a 15-m maximal sprint every minute and self-paced exercise bouts of varying intensities. Muscle biopsies were extracted before and after exercise during the baseline session and before exercise on day 2 during experimental trials. Voluntary force and activation of the right quadriceps, nude mass, HR, core temperature, capillary blood lactate and glucose, RPE, and a modified POMS were recorded before, after, and during the exercise protocols.

RESULTS

Mean sprint times were slower on SDEP2 (2.78±0.17 s) compared with SDEP1 (2.70±0.16 s) and CONT2 (2.74±0.15 s, P<0.05). Distance covered during self-paced exercise was reduced during SDEP2 during the initial 10 min compared with SDEP1 and during the final 10 min compared with CONT2 (P<0.05). Muscle glycogen concentration was lower before exercise on SDEP2 (209±60 mmol·kg dry weight) compared with CONT2 (274±54 mmol·kg dry weight, P=0.05). Voluntary force and activation were reduced on day 2 of both conditions; however, both were lower in SDEP2 compared with CONT2 (P<0.05). Sleep loss did not affect RPE but negatively affected POMS ratings (P<0.05).

CONCLUSIONS

Sleep loss and associated reductions in muscle glycogen and perceptual stress reduced sprint performance and slowed pacing strategies during intermittent-sprint exercise for male team-sport athletes.

Neuromuscular adjustments that constrain submaximal EMG amplitude at task failure of sustained isometric contractions

The amplitude of the surface EMG does not reach the level achieved during a maximal voluntary contraction force at the end of a sustained, submaximal contraction, despite near-maximal levels of voluntary effort. The depression of EMG amplitude may be explained by several neural and muscular adjustments during fatiguing contractions, including decreased net neural drive to the muscle, changes in the shape of the motor unit action potentials, and EMG amplitude cancellation. The changes in these parameters for the entire motor unit pool, however, cannot be measured experimentally. The present study used a computational model to simulate the adjustments during sustained isometric contractions and thereby determine the relative importance of these factors in explaining the submaximal levels of EMG amplitude at task failure. The simulation results indicated that the amount of amplitude cancellation in the simulated EMG (∼ 40%) exhibited a negligible change during the fatiguing contractions. Instead, the main determinant of the submaximal EMG amplitude at task failure was a decrease in muscle activation (number of muscle fiber action potentials), due to a reduction in the net synaptic input to motor neurons, with a lesser contribution from changes in the shape of the motor unit action potentials. Despite the association between the submaximal EMG amplitude and reduced muscle activation, the deficit in EMG amplitude at task failure was not consistently associated with the decrease in neural drive (number of motor unit action potentials) to the muscle. This indicates that the EMG amplitude cannot be used as an index of neural drive.

Effects of different pedalling techniques on muscle fatigue and mechanical efficiency during prolonged cycling

The present study aimed to test the influence of the pedalling technique on the occurrence of muscular fatigue and on the energetic demand during prolonged constant-load cycling exercise. Subjects performed two prolonged (45 min) cycling sessions at constant intensity (75% of maximal aerobic power). In a random order, participants cycled either with their preferred technique (PT) during one session or were helped by a visual force-feedback to modify their pedalling pattern during the other one (FB). Index of pedalling effectiveness was significantly (P<0.05) improved during FB (41.4 ± 5.5%); compared with PT (36.6 ± 4.1%). Prolonged cycling induced a significant reduction of maximal power output, which was greater after PT (-15 ± 9%) than after FB (-7 ± 12%). During steady-state FB, vastus lateralis muscle activity was significantly (P<0.05) reduced, whereas biceps femoris muscles activities increased compared with PT. Gross efficiency (GE) did not significantly differ between the two sessions, except during the first 15 min of exercise (FB: 19.0 ± 1.9% vs PT: 20.2 ± 1.9%). Although changes in muscular coordination pattern with feedback did not seem to influence GE, it could be mainly responsible for the reduction of muscle fatigue after prolonged cycling.

Cerebral oxygenation decreases but does not impair performance during self-paced, strenuous exercise

AIM

The reduction in cerebral oxygenation (Cox) is associated with the cessation of exercise during constant work rate and incremental tests to exhaustion. Yet in exercises of this nature, ecological validity is limited due to work rate being either fully or partly dictated by the protocol, and it is unknown whether cerebral deoxygenation also occurs during self-paced exercise. Here, we investigated the cerebral haemodynamics during a 5-km running time trial in trained runners.

METHODS

Rating of perceived exertion (RPE) and surface electromyogram (EMG) of lower limb muscles were recorded every 0.5 km. Changes in Cox (prefrontal lobe) were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxyhaemoglobin (Delta[O(2)Hb], Delta[HHb]). Changes in total Hb were calculated (Delta[THb] = Delta[O(2)Hb] + Delta[HHb]) and used as an index of change in regional blood volume.

RESULTS

During the trial, RPE increased from 6.6 +/- 0.6 to 19.1 +/- 0.7 indicating maximal exertion. Cox rose from baseline to 2.5 km ( upward arrowDelta[O(2)Hb], upward arrowDelta[HHb], upward arrowDelta[THb]), remained constant between 2.5 and 4.5 km, and fell from 4.5 to 5 km ( downward arrowDelta[O(2)Hb], upward arrowDelta[HHb], <-->Delta[THb]). Interestingly, the drop in Cox at the end of the trial coincided with a final end spurt in treadmill speed and concomitant increase in skeletal muscle recruitment (as revealed by higher lower limb EMG).

CONCLUSION

Results confirm the large tolerance for change in Cox during exercise at sea level, yet further indicate that, in conditions of self-selected work rate, cerebral deoxygenation remains within a range that does not hinder strenuous exercise performance.

Effect of performance level on pacing strategy during a 10-km running race

The aim of this study was to examine the influence of the performance level of athletes on pacing strategy during a simulated 10-km running race, and the relationship between physiological variables and pacing strategy. Twenty-four male runners performed an incremental exercise test on a treadmill, three 6-min bouts of running at 9, 12 and 15 km h(-1), and a self-paced, 10-km running performance trial; at least 48 h separated each test. Based on 10-km running performance, subjects were divided into terziles, with the lower terzile designated the low-performing (LP) and the upper terzile designated the high-performing (HP) group. For the HP group, the velocity peaked at 18.8 +/- 1.4 km h(-1) in the first 400 m and was higher than the average race velocity (P < 0.05). The velocity then decreased gradually until 2,000 m (P < 0.05), remaining constant until 9,600 m, when it increased again (P < 0.05). The LP group ran the first 400 m at a significantly lower velocity than the HP group (15.6 +/- 1.6 km h(-1); P > 0.05) and this initial velocity was not different from LP average racing velocity (14.5 +/- 0.7 km h(-1)). The velocity then decreased non-significantly until 9,600 m (P > 0.05), followed by an increase at the end (P < 0.05). The peak treadmill running velocity (PV), running economy (RE), lactate threshold (LT) and net blood lactate accumulation at 15 km h(-1) were significantly correlated with the start, middle, last and average velocities during the 10-km race. These results demonstrate that high and low performance runners adopt different pacing strategies during a 10-km race. Furthermore, it appears that important determinants of the chosen pacing strategy include PV, LT and RE.

Electromyographic evaluation of upper limb muscles involved in armwrestling sport simulation during dynamic and static conditions

OBJECTIVE

To evaluate the electromyographic activity of the Pectoralis Major (PM), Biceps Brachii (BB), Pronator Teres (PT) and Flexor Carpi Ulnaris (FCU) muscles involved in simulated armwrestling.

METHODS

Ten trained volunteers were selected to perform the armwrestling movement, during dynamic tests with 40% and 80% of maximum voluntary load (MVL) and static tests in the initial, intermediary and final positions. Electromyographic and force data were normalized for analyses.

RESULTS

In dynamic tests with 40% MVL, electric activity of the PT muscle was greater than FCU (p<0.01) and BB (p<0.05) muscles, and with 80% MVL, PM and PT muscles were the most active. In static tests, electric activity increased from the initial to final positions for the PM muscle (p<0.05), while it decreased for the BB and PT muscles (p<0.001 and p<0.05, respectively). No significant changes were observed for force and no correlation was found with the simultaneous electric activity.

CONCLUSIONS

It can be concluded that the PM and FCU muscles participate as agonists in the simulated armwrestling whereas the BB and PT muscles seem to perform secondary functions. Electric activity showed to be dependent on the load and on the position of the upper limb, but not on the force produced during the movement.

Is it time to retire the 'central governor'?

Over the past 13 years, Noakes and his colleagues have argued repeatedly for the existence of a 'Central Governor', a specific brain centre that provides a feed-forward regulation of the intensity of vigorous effort in order to conserve homeostasis, protecting vital organs such as the brain, heart and skeletal muscle against damage from hyperthermia, ischaemia and other manifestations of catastrophic failure. This brief article reviews evidence concerning important corollaries of the hypothesis, examining the extent of evolutionary pressures for the development of such a mechanism, the effectiveness of protection against hyperthermia and ischaemia during exhausting exercise, the absence of peripheral factors limiting peak performance (particularly a plateauing of cardiac output and oxygen consumption) and proof that electromyographic activity is limiting exhausting effort. As yet, there is a lack of convincing experimental evidence to support these corollaries of the hypothesis; furthermore, some findings, such as the rather consistent demonstration of an oxygen consumption plateau in young adults, argue strongly against the limiting role of a 'Central Governor'.