Effect of blood lactate concentration and the level of oxygen uptake immediately before a cycling sprint on neuromuscular activation during repeated cycling sprints

Neuromuscular Fatigue Responses of Endurance- and Strength-Trained Athletes during Incremental Cycling Exercise

This study explored the development of neuromuscular fatigue responses during progressive cycling exercise. The sample comprised 32 participants aged 22.0 ± 0.54 years who were assigned into three groups: endurance-trained group (END, triathletes, n = 10), strength-trained group (STR, bodybuilders, n = 10) and control group (CG, recreationally active students, n = 12). The incremental cycling exercise was performed using a progressive protocol starting with a 3 min resting measurement and then 50 W workload with subsequent constant increments of 50 W every 3 min until 200 W. Surface electromyography (SEMG) of rectus femoris muscles was recorded during the final 30 s of each of the four workloads. During the final 15 s of each workload, participants rated their overall perception of effort using the 20-point rating of the perceived exertion (RPE) scale. Post hoc Tukey’s HSD testing showed significant differences between the END and STR groups in median frequency and mean power frequency across all workloads (p < 0.001 and p < 0.01, respectively). Athletes from the END group had significantly lower electromyogram amplitude responses than those from the STR (p = 0.0093) and CG groups (p = 0.0006). Increasing RPE points from 50 to 200 W were significantly higher in the STR than in the END group (p < 0.001). In conclusion, there is a significant variation in the neuromuscular fatigue profiles between athletes with different training backgrounds when a cycling exercise is applied. The approximately linear trends of the SEMG and RPE values of both groups of athletes with increasing workload support the increased skeletal muscle recruitment with perceived exertion or fatiguing effect.

Neuromuscular Adjustments Following Sprint Training with Ischemic Preconditioning in Endurance Athletes: Preliminary Data

This preliminary study examined the effect of chronic ischemic preconditioning (IPC) on neuromuscular responses to high-intensity exercise. In a parallel-group design, twelve endurance-trained males (VO₂max 60.0 ± 9.1 mL·kg⁻¹·min⁻¹) performed a 30-s Wingate test before, during, and after 4 weeks of sprint-interval training. Training consisted of bi-weekly sessions of 4 to 7 supra-maximal all-out 30-s cycling bouts with 4.5 min of recovery, preceded by either IPC (3 × 5-min of compression at 220 mmHg/5-min reperfusion, IPC, n = 6) or placebo compressions (20 mmHg, PLA, n = 6). Mechanical indices and the root mean square and mean power frequency of the electromyographic signal from three lower-limb muscles were continuously measured during the Wingate tests. Data were averaged over six 5-s intervals and analyzed with Cohen’s effect sizes. Changes in peak power output were not different between groups. However, from mid- to post-training, IPC improved power output more than PLA in the 20 to 25-s interval (7.6 ± 10.0%, ES 0.51) and the 25 to 30-s interval (8.8 ± 11.2%, ES 0.58), as well as the fatigue index (10.0 ± 2.3%, ES 0.46). Concomitantly to this performance difference, IPC attenuated the decline in frequency spectrum throughout the Wingate (mean difference: 14.8%, ES range: 0.88–1.80). There was no difference in root mean square amplitude between groups. These preliminary results suggest that using IPC before sprint training may enhance performance during a 30-s Wingate test, and such gains occurred in the last 2 weeks of the intervention. This improvement may be due, in part, to neuromuscular adjustments induced by the chronic use of IPC.

Neuro-mechanical determinants of repeated treadmill sprints - Usefulness of an "hypoxic to normoxic recovery" approach

To improve our understanding of the limiting factors during repeated sprinting, we manipulated hypoxia severity during an initial set and examined the effects on performance and associated neuro-mechanical alterations during a subsequent set performed in normoxia. On separate days, 13 active males performed eight 5-s sprints (recovery = 25 s) on an instrumented treadmill in either normoxia near sea-level (SL; FiO₂ = 20.9%), moderate (MH; FiO₂ = 16.8%) or severe normobaric hypoxia (SH; FiO₂ = 13.3%) followed, 6 min later, by four 5-s sprints (recovery = 25 s) in normoxia. Throughout the first set, along with distance covered [larger sprint decrement score in SH (−8.2%) compared to SL (−5.3%) and MH (−7.2%); P < 0.05], changes in contact time, step frequency and root mean square activity (surface electromyography) of the quadriceps (Rectus femoris muscle) in SH exceeded those in SL and MH (P < 0.05). During first sprint of the subsequent normoxic set, the distance covered (99.6, 96.4, and 98.3% of sprint 1 in SL, MH, and SH, respectively), the main kinetic (mean vertical, horizontal, and resultant forces) and kinematic (contact time and step frequency) variables as well as surface electromyogram of quadriceps and plantar flexor muscles were fully recovered, with no significant difference between conditions. Despite differing hypoxic severity levels during sprints 1–8, performance and neuro-mechanical patterns did not differ during the four sprints of the second set performed in normoxia. In summary, under the circumstances of this study (participant background, exercise-to-rest ratio, hypoxia exposure), sprint mechanical performance and neural alterations were largely influenced by the hypoxia severity in an initial set of repeated sprints. However, hypoxia had no residual effect during a subsequent set performed in normoxia. Hence, the recovery of performance and associated neuro-mechanical alterations was complete after resting for 6 min near sea level, with a similar fatigue pattern across conditions during subsequent repeated sprints in normoxia.

Effects of heat exposure in the absence of hyperthermia on power output during repeated cycling sprints

The aim of this study was to investigate the effects of heat exposure in the absence of hyperthermia on power output during repeated cycling sprints. Seven males performed four 10-s cycling sprints interspersed by 30 s of active recovery on a cycle ergometer in hot-dry and thermoneutral environments. Changes in rectal temperature were similar under the two ambient conditions. The mean 2-s power output over the 1st–4th sprints was significantly lower under the hot-dry condition than under the thermoneutral condition. The amplitude of the electromyogram was lower under the hot-dry condition than under the thermoneutral condition during the early phase (0–3 s) of each cycling sprint. No significant difference was observed for blood lactate concentration between the two ambient conditions. Power output at the onset of a cycling sprint during repeated cycling sprints is decreased due to heat exposure in the absence of hyperthermia.

Electromyography normalization methods for high-velocity muscle actions: review and recommendations

Electromyograms used to assess neuromuscular demand during high-velocity tasks require normalization to aid interpretation. This paper posits that, to date, methodological approaches to normalization have been ineffective and have limited the application of electromyography (EMG). There is minimal investigation seeking alternative normalization methods, which must be corrected to improve EMG application in sports. It is recognized that differing normalization methods will prevent cross-study comparisons. Users of EMG should aim to identify normalization methods that provide good reliability and a representative measure of muscle activation. The shortcomings of current normalization methods in high-velocity muscle actions assessment are evident. Advances in assessing alternate normalization methods have been done in cycling and sprinting. It is advised that when normalizing high-intensity muscle actions, isometric methods are used with caution and a dynamic alternative, where the muscle action is similar to that of the task is preferred. It is recognized that optimal normalization methods may be muscle and task dependent.

Effects of prior short multiple-sprint exercises with different intersprint recoveries on the slow component of oxygen uptake during high-intensity exercise

This study compares the effects of two short multiple-sprint exercise (MSE) (6 × 6 s) sessions with two different recovery durations (30 s or 180 s) on the slow component of oxygen uptake ([Formula: see text]O2) during subsequent high-intensity exercise. Ten male subjects performed a 6-min cycling test at 50% of the difference between the gas exchange threshold and [Formula: see text]O2peak (Δ50). Then, the subjects performed two MSEs of 6 × 6 s separated by two intersprint recoveries of 30 s (MSE30) and 180 s (MSE180), followed 10 min later by the Δ50 (Δ5030 and Δ50180, respectively). Electromyography (EMG) activities of the vastus medialis and lateralis were measured throughout each exercise bout. During MSE30, muscle activity (root mean square) increased significantly (p ≤ 0.04), with a significant leftward-shifted median frequency of the power density spectrum (MDF; p ≤ 0.01), whereas MDF was significantly rightward-shifted during MSE180 (p = 0.02). The mean [Formula: see text]O2 value was significantly higher in MSE30 than in MSE180 (p < 0.001). During Δ5030, [Formula: see text]O2 and the deoxygenated hemoglobin ([HHb]) slow components were significantly reduced (–27%, p = 0.02, and –34%, p = 0.003, respectively) compared with Δ50. There were no significant modifications of the [Formula: see text]O2 slow component in Δ50180 compared with Δ50 (p = 0.32). The neuromuscular and metabolic adaptations during MSE30 (preferential activation of type I muscle fibers evidenced by decreased MDF and a greater aerobic metabolism contribution to the required energy demands), but not during MSE180, may lead to reduced [Formula: see text]O2 and [HHb] slow components, suggesting an alteration in motor units recruitment profile (i.e., change in the type of muscle fibers recruited) and (or) an improved muscle O2 delivery during subsequent exercise.

Effects of humoral factors on ventilation kinetics during recovery after impulse-like exercise

To clarify the ventilatory kinetics during recovery after impulse-like exercise, subjects performed one impulse-like exercise test (one-impulse) and a five-times repeated impulse-like exercises test (five-impulse). Duration and intensity of the impulse-like exercise were 20 sec and 400 watts (80 rpm), respectively. Although blood pH during recovery (until 10 min) was significantly lower in the five-impulse test than in the one-impulse test, ventilation (.VE) in the two tests was similar except during the first 30 sec of recovery, in which it was higher in the five-impulse test. In one-impulse, blood CO2 pressure (PCO2) was significantly increased at 1 min during recovery and then returned to the pre-exercise level at 5 min during recovery. In the five-impulse test, PCO2 at 1 min during recovery was similar to the pre-exercise level, and then it decreased to a level lower than the pre-exercise level at 5 min during recovery. Accordingly, PCO2 during recovery (until 30 min) was significantly lower in the five-impulse than in one-impulse test..VE and pH during recovery showed a curvilinear relationship, and at the same pH, ventilation was higher in the one-impulse test. These results suggest that ventilatory kinetics during recovery after impulse-like exercise is attributed partly to pH, but the stimulatory effect of lower pH is diminished by the inhibitory effect of lower PCO2.

Repeated-sprint ability - part I: factors contributing to fatigue

Short-duration sprints (<10 seconds), interspersed with brief recoveries (<60 seconds), are common during most team and racket sports. Therefore, the ability to recover and to reproduce performance in subsequent sprints is probably an important fitness requirement of athletes engaged in these disciplines, and has been termed repeated-sprint ability (RSA). This review (Part I) examines how fatigue manifests during repeated-sprint exercise (RSE), and discusses the potential underpinning muscular and neural mechanisms. A subsequent companion review to this article will explain a better understanding of the training interventions that could eventually improve RSA. Using laboratory and field-based protocols, performance analyses have consistently shown that fatigue during RSE typically manifests as a decline in maximal/mean sprint speed (i.e. running) or a decrease in peak power or total work (i.e. cycling) over sprint repetitions. A consistent result among these studies is that performance decrements (i.e. fatigue) during successive bouts are inversely correlated to initial sprint performance. To date, there is no doubt that the details of the task (e.g. changes in the nature of the work/recovery bouts) alter the time course/magnitude of fatigue development during RSE (i.e. task dependency) and potentially the contribution of the underlying mechanisms. At the muscle level, limitations in energy supply, which include energy available from phosphocreatine hydrolysis, anaerobic glycolysis and oxidative metabolism, and the intramuscular accumulation of metabolic by-products, such as hydrogen ions, emerge as key factors responsible for fatigue. Although not as extensively studied, the use of surface electromyography techniques has revealed that failure to fully activate the contracting musculature and/or changes in inter-muscle recruitment strategies (i.e. neural factors) are also associated with fatigue outcomes. Pending confirmatory research, other factors such as stiffness regulation, hypoglycaemia, muscle damage and hostile environments (e.g. heat, hypoxia) are also likely to compromise fatigue resistance during repeated-sprint protocols.

A influência da fadiga neuromuscular e da acidose metabólica sobre a corrida de 400 metros

Exercícios inabituais podem levar a danos musculares que persistem por alguns dias diminuindo a capacidade de desempenho em decorrência da fadiga. Além disso, o aumento da acidose intramuscular pode limitar o metabolismo celular no processo de gerar trabalho. Com isso, esta pesquisa teve como finalidade analisar a influência da fadiga neuromuscular e da acidose metabólica sobre a corrida de 400 metros. Foram selecionados 20 indivíduos, sedentários, com idade entre 18 e 35 anos. Estes foram submetidos aos seguintes protocolos: teste incremental em esteira, para determinação do VO2max; limiares aeróbio e anaeróbio, teste de 400m (400/C), atividade pliométrica, com repouso ativo/passivo, seguida de corrida de 400m logo após (400/Pós) e 24 horas após a atividade pliométrica (400/24h). Os resultados obtidos mostram que, quando comparados os grupos ativo e passivo, não apresentaram diferenças significantes no desempenho dos 400/ Pós, mas o tempo deste foi maior, para os dois grupos quando comparado com os 400/C. No entanto, o 400/24h não foi significantemente diferente quando comparado com o 400/C para ambos os grupos. Concluise que, independente do tipo de recuperação - ativa ou passiva -, a diminuição de desempenho em uma corrida de 400 metros após atividade pliométrica parece ser ocasionada por mecanismos neuromusculares que levam à fadiga e não a limitações metabólicas.

Effect of oral administration of sodium bicarbonate on surface EMG activity during repeated cycling sprints

The purpose of this study was to determine the effect of oral administration of sodium bicarbonate (NaHCO3) on surface electromyogram (SEMG) activity from the vastus lateralis (VL) during repeated cycling sprints (RCS). Subjects performed two RCS tests (ten 10-s sprints) interspersed with both 30-s and 360-s recovery periods 1 h after oral administration of either NaHCO3 (RCSAlk) or CaCO3 (RCSPla) in a random counterbalanced order. Recovery periods of 360 s were set before the 5th and 9th sprints. The rate of decrease in plasma HCO3- concentration during RCS was significantly greater in RCSAlk than in RCSPla, but the rates of decline in blood pH during the two RCS tests were similar. There was no difference between change in plasma lactate concentration in RCSAlk and that in RCSPla. Performance during RCSAlk was similar to that during RCSPla. There were no differences in oxygen uptake immediately before each cycling sprint (preVO2) and in SEMG activity between RCSAlk and RCSPla. In conclusion, oral administration of NaHCO3 did not affect SEMG activity from the VL. This suggests that the muscle recruitment strategy during RCS is not determined by only intramuscular pH.

A 350-S recovery period does not necessarily allow complete recovery of peak power output during repeated cycling sprints

The aim of this study was to determine whether a 350-s recovery period allows recovery of peak power output (PPO) to its initial value under the condition of a blood lactate (La) concentration higher than 10 mmol.L-1 during repeated cycling sprints (RCS). RCS (10x10-s cycling sprints) were performed under two conditions. Under one condition, the recovery period of RCS was fixed at 35 s (RCS35), and under the other condition, a 350-s recovery period was set before the 5th and 9th sets, and a 35-s recovery period was set before the other sets (RCScomb). In RCScomb, PPO in the 5th set recovered to that in the 1st set, but PPO in the 9th set did not. Under both conditions, blood La concentration progressively increased and reached approximately 14 mmol.L-1 at the end of the RCS. In RCScomb, VO2 immediately before the 5th set was not significantly different from that immediately before the 9th set. Mean power frequency (MPF) values estimated by a surface electromyogram from the vastus lateralis in the 5th and 9th sets were significantly higher in RCScomb than in RCS35. In conclusion, a 350-s recovery period does not allow recovery of PPO to its initial value under the condition of a blood La concentration of 14 mmol.L-1 during RCS.