Influence of averaging method on muscle deoxygenation interpretation during repeated-sprint exercise.

Near-infrared spectroscopy (NIRS) is a common tool used to study oxygen availability and utilization during repeated-sprint exercise. However, there are inconsistent methods of smoothing and determining peaks and nadirs from the NIRS signal, which make interpretation and comparisons between studies difficult. To examine the effects of averaging method on deoxyhaemoglobin concentration ([HHb]) trends, nine males performed ten 10-s sprints, with 30 seconds of recovery, and six analysis methods were used for determining peaks and nadirs in the [HHb] signal. First, means were calculated over predetermined windows in the last 5 and 2 seconds of each sprint and recovery period. Second, moving 5-seconds and 2-seconds averages were also applied, and peaks/nadirs were determined for each 40-seconds sprint/recovery cycle. Third, a Butterworth filter was used to smooth the signal, and the resulting signal output was used to determine peaks and nadirs from predetermined time points and a rolling approach. Correlation and residual analysis showed that the Butterworth filter attenuated the "noise" in the signal, while maintaining the integrity of the raw data (r = .9892; mean standardized residual -9.71 × 103  ± 3.80). Means derived from predetermined windows, irrespective of length and data smoothing, underestimated the magnitude of peak and nadir [HHb] compared to a rolling mean approach. Consequently, sprint-induced metabolic changes (inferred from Δ[HHb]) were underestimated. Based on these results, we suggest using a digital filter to smooth NIRS data, rather than an arithmetic mean, and a rolling approach to determine peaks and nadirs for accurate interpretation of muscle oxygenation trends.

Brain oxygenation declines in elite Kenyan runners during a maximal interval training session.

PURPOSE: The purpose of this study was to characterise the cerebral oxygenation (Cox) response during a high-intensity interval training session in Kenyan runners, and to examine any relationship with running performance. METHODS: 15 Kenyan runners completed a 5-km time trial (TT) and a Fatigue Training Test on a treadmill (repeated running bouts of 1-km at a pace 5% faster than their mean 5-km TT pace with a 30-s recovery until exhaustion). Changes in Cox were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxy-haemoglobin (Δ[O2Hb] and Δ[HHb]), tissue oxygenation index (TOI), and total hemoglobin index (nTHI). RESULTS: The number of 1-km repetitions achieved by the participants was 5.5 ± 1.2 repetitions at a mean pace of 20.5 ± 0.7 km h-1. Δ[O2Hb] measured at the end of each running repetition declined progressively over the course of the trial (p = 0.01, ES = 4.59). Δ[HHb] increased during each running bout until the end of the Fatigue Training Test (p < 0.001; ES = 6.0). TOI decreased significantly from the beginning of the test (p = 0.013, ES = 1.83), whereas nTHI remained stable (ES = 0.08). The Cox decline in the Fatigue Training Test was negatively correlated with the speed at which the test was completed (p = 0.017; r = -0.61), suggesting that the best performers were able to defend their Cox better than those of lower running ability. CONCLUSIONS: In conclusion, this study suggests that elite Kenyan runners cannot defend cerebral oxygenation when forced to exercise to their physiological limits. This emphasises the critical importance of pacing in their racing success.

Cold-water immersion decreases cerebral oxygenation but improves recovery after intermittent-sprint exercise in the heat.

This study examined the effects of post-exercise cooling on recovery of neuromuscular, physiological, and cerebral hemodynamic responses after intermittent-sprint exercise in the heat. Nine participants underwent three post-exercise recovery trials, including a control (CONT), mixed-method cooling (MIX), and cold-water immersion (10 °C; CWI). Voluntary force and activation were assessed simultaneously with cerebral oxygenation (near-infrared spectroscopy) pre- and post-exercise, post-intervention, and 1-h and 24-h post-exercise. Measures of heart rate, core temperature, skin temperature, muscle damage, and inflammation were also collected. Both cooling interventions reduced heart rate, core, and skin temperature post-intervention (P < 0.05). CWI hastened the recovery of voluntary force by 12.7 ± 11.7% (mean ± SD) and 16.3 ± 10.5% 1-h post-exercise compared to MIX and CONT, respectively (P < 0.01). Voluntary force remained elevated by 16.1 ± 20.5% 24-h post-exercise after CWI compared to CONT (P < 0.05). Central activation was increased post-intervention and 1-h post-exercise with CWI compared to CONT (P < 0.05), without differences between conditions 24-h post-exercise (P > 0.05). CWI reduced cerebral oxygenation compared to MIX and CONT post-intervention (P < 0.01). Furthermore, cooling interventions reduced cortisol 1-h post-exercise (P < 0.01), although only CWI blunted creatine kinase 24-h post-exercise compared to CONT (P < 0.05). Accordingly, improvements in neuromuscular recovery after post-exercise cooling appear to be disassociated with cerebral oxygenation, rather reflecting reductions in thermoregulatory demands to sustain force production.

Anthropometric characteristics account for time to exhaustion in cycling.

This study examined the relationship between the phenotypic and anthropometric characteristics and the cycling time to exhaustion (Tlim) at the maximal aerobic power output (Pmax). 12 (7 men, 5 women) physically-active participants performed a square-wave test at Pmax to determine the maximal time limit. Muscle histochemistry, enzymatic activities and buffer capacity were determined from a vastus lateralis muscle biopsy, lean body mass (LBM) by hydrostatic weighing, and total (TV) and lean (LV) volumes of the thigh by anthropometric measurements. The mean (±SD) Tlim was 235±84 s (score range: 108-425 s). No relationship was found between Tlim and any muscle phenotypes. However, we observed a strong, linear relationship between Tlim and LBM (r=0.84, P<0.05). Thigh TV and LV displayed weaker correlation coefficients with Tlim (r=0.66 and r=0.73, respectively; P<0.05). We further estimated the femur length and found this measure to correlate with Tlim (r=0.81, P<0.05). This study suggests that muscle phenotypes may not be representative of Tlim. Rather, anthropometric characteristics account for such performance by conferring a biomechanical advantage in cycling. We conclude that, in addition to metabolic factors, anthropometric characteristics with reasonable accuracy predict Tlim in cycling, and may account for the large inter-subject variability observed in previous studies.

Repeated-sprint performance and vastus lateralis oxygenation: effect of limited O2 availability.

This study examined the influence of muscle deoxygenation and reoxygenation on repeated-sprint performance via manipulation of O2 delivery. Fourteen team-sport players performed 10 10-s sprints (30-s recovery) under normoxic (NM: FI O2 0.21) and acute hypoxic (HY: FI O2 0.13) conditions in a randomized, single-blind fashion and crossover design. Mechanical work was calculated and arterial O2 saturation (Sp O2 ) was estimated via pulse oximetry for every sprint. Muscle deoxyhemoglobin concentration ([HHb]) was monitored continuously by near-infrared spectroscopy. Differences between NM and HY data were analyzed for practical significance using magnitude-based inferences. HY reduced Sp O2 (-10.7 ± 1.9%, with chances to observe a higher/similar/lower value in HY of 0/0/100%) and mechanical work (-8.2 ± 2.1%; 0/0/100%). Muscle deoxygenation increased during sprints in both environments, but was almost certainly higher in HY (12.5 ± 3.1%, 100/0/0%). Between-sprint muscle reoxygenation was likely more attenuated in HY (-11.1 ± 11.9%; 2/7/91%). The impairment in mechanical work in HY was very largely correlated with HY-induced attenuation in muscle reoxygenation (r = 0.78, 90% confidence limits: 0.49; 0.91). Repeated-sprint performance is related, in part, to muscle reoxygenation capacity during recovery periods. These results extend previous findings that muscle O2 availability is important for prolonged repeated-sprint performance, in particular when the exercise is taken in hypoxia.

Physiological demands of a simulated BMX competition.

The aim of this study was to investigate the physiological demands of Supercross BMX in elite athletes. Firstly athletes underwent an incremental cycling test to determine maximal oxygen uptake (VO2max) and power at ventilatory thresholds. In a second phase, athletes performed alone a simulated competition, consisting of 6 cycling races separated by 30 min of passive recovery on an actual BMX track. Oxygen uptake, blood lactate, anion gap and base excess (BE) were measured. Results indicated that a simulated BMX performed by elite athletes induces a high solicitation of both aerobic (mean peak VO2 (VO2peak): 94.3±1.2% VO2max) and anaerobic glycolysis (mean blood lactate: 14.5±4. 5 mmol x L(-1) during every race. Furthermore, the repetition of the 6 cycling races separated by 30 min of recovery led to a significant impairment of the acid-base balance from the third to the sixth race (mean decrease in BE: -18.8±7.5%, p<0.05). A significant relationship was found between the decrease in BE and VO2peak (r = - 0.73, p<0.05), indicating that VO2peak could explain for 54% of the variation in BMX performance. These results suggest that both oxygen-dependent and -independent fuel substrate pathways are important determinants of BMX performance.

Maintained cerebral oxygenation during maximal self-paced exercise in elite Kenyan runners.

The purpose of this study was to analyze the cerebral oxygenation response to maximal self-paced and incremental exercise in elite Kenyan runners from the Kalenjin tribe. On two separate occasions, 15 elite Kenyan distance runners completed a 5-km time trial (TT) and a peak treadmill speed test (PTS). Changes in cerebral oxygenation were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxyhemoglobin (Δ[O2Hb] and Δ[HHb]), tissue oxygenation index (TOI), and total hemoglobin index (nTHI). During the 5-km TT (15.2 ± 0.2 min), cerebral oxygenation increased over the first half (increased Δ[O2Hb] and Δ[HHb]) and, thereafter, Δ[O2Hb] remained constant (effect size, ES = 0.33, small effect), whereas Δ[HHb] increased until the end of the trial (P < 0.05, ES = 3.13, large effect). In contrast, during the PTS, from the speed corresponding to the second ventilatory threshold, Δ[O2Hb] decreased (P < 0.05, ES = 1.51, large effect), whereas Δ[HHb] continued to increase progressively until exhaustion (P < 0.05, ES = 1.22, large effect). Last, the TOI was higher during the PTS than during the 5-km TT (P < 0.001, ES = 3.08; very large effect), whereas nTHI values were lower (P < 0.001, ES = 2.36, large effect). This study shows that Kenyan runners from the Kalenjin tribe are able to maintain their cerebral oxygenation within a stable range during a self-paced maximal 5-km time trial, but not during an incremental maximal test. This may contribute to their long-distance running success.

Cortical current density oscillations in the motor cortex are correlated with muscular activity during pedaling exercise.

Despite modern imaging techniques, assessing and localizing changes in brain activity during whole-body exercise is still challenging. Using an active electroencephalography (EEG) system in combination with source localization algorithms, this study aimed to localize brain cortical oscillations patterns in the motor cortex and to correlate these with surface electromyography (EMG)-detected muscular activity during pedaling exercise. Eight subjects performed 2-min isokinetic (90 rpm) cycling bouts at intensities ranging from 1 to 5 Wkg(-1) body mass on a cycle ergometer. These bouts were interspersed by a minimum of 2 min of passive rest to limit to development of peripheral muscle fatigue. Brain cortical activity within the motor cortex was analyzed using a 32-channel active EEG system combined with source localization algorithms. EMG activity was recorded from seven muscles on each lower limb. EEG and EMG activity revealed comparatively stable oscillations across the different exercise intensities. More importantly, the oscillations in cortical activity within the motor cortex were significantly correlated with EMG activity during the high-intensity cycling bouts. This study demonstrates that it is possible to localize oscillations in brain cortical activity during moderate- to high-intensity cycling exercise using EEG in combination with source localization algorithms, and that these oscillations match the activity of the active muscles in time and amplitude. Results of this study might help to further evaluate the effects of central vs. peripheral fatigue during exercise.

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.

Effects of the time of day on repeated all-out cycle performance and short-term recovery patterns.

The effect of the time of day on repeated cycle sprint performance and short-term recovery patterns was investigated in 12 active male subjects (23+/-2 years, 76.4+/-4.2 kg, 1.80+/-0.06 m, 9.5+/-4.5 h . week (-1) of physical activity). Subjects performed ten 6-s maximal sprints inter-spaced by 30 s rest in the morning (08 : 00-10 : 00 h) and in the evening (17 : 00-19 : 00 h) on separate days. During the intermittent exercise, peak power output (P (PO), watts), total mechanical work (W, kJ), peak pedalling rate (P (PR), rev . min (-1)), and peak efficient torque (P (TCK), Nm) were recorded. The values at the 1st, the 5th, and the 10th sprints were used as mechanical indices of fatigue occurrence. Intra-aural temperature and maximal voluntary contraction of knee extensors muscles (MVC) were measured before (pre), immediately after (post) the cycle bouts and following a 5-min passive recovery period (post 5). The MVC indices were used to further confirm occurrence of neuromuscular fatigue and to assess short-term recovery patterns from all-out intermittent effort. During the MVC, electromyographic activity of the vastus lateralis muscle was recorded and analysed as its root mean square (RMS). The torque produced per unit RMS was calculated and used as index of neuromuscular efficiency (NME). A main effect for the sprint number was observed for all cycle performance parameters (p<0.05). The main effect for the time of day was not significant for any biomechanical indices of neuromuscular performance. A significant interaction effect of the time of day and the sprint repetition was demonstrated on P (TCK) ( F(2,22)=4.3, p<0.05). The decrease in P (TCK) consecutive to sprint repetition was sharper in the evening compared to the morning (sprint 10[% of sprint 1]:-9.5 % in the evening vs. - 2.2 % in the morning, p<0.05). Significant interaction effects of the time of day and the condition (i. e. pre, post, post 5) were also demonstrated for RMS ( F(2,22)=3.6, p<0.05) and NME ( F(2,22)=4.5, p<0.05) during MVC. These interactions were characterised by similar patterns of fatigue occurrence (i. e. post vs. pre condition) in the morning (+7.5 % for RMS, - 19.6 % for NME) as in the evening (+10.2 % for RMS, -19.4 % for NME) but different patterns of short-term recovery (i. e. post 5 vs. post condition; p<0.05) in the morning (-7.3 % for RMS, +13.7 % for NME) compared to the evening (+3.3 % for RMS, -1.8 % for NME). These results suggest that short-term recovery patterns of neuromuscular function are slower in the evening compared to the morning.

Effect of high-intensity intermittent cycling sprints on neuromuscular activity.

High-intensity intermittent sprints induce changes in metabolic and mechanical parameters. However, very few data are available about electrical manifestations of muscle fatigue following such sprints. In this study, quadriceps electromyographic (EMG) responses to repeated all-out exercise bouts of short duration were assessed from maximal voluntary isometric contractions (MVC) performed before and after sprints. Twelve men performed ten 6-s maximal cycling sprints, separated by 30-s rest. The MVC were performed pre-sprints ( pre), post-sprints ( post), and 5 min post-sprints ( post5). Values of root-mean-square (RMS) and median frequency (MF) of vastus lateralis (VL) and vastus medialis (VM) were recorded during each MVC. During sprints, PPO decreased significantly in sprints 8, 9, and 10, compared to sprint 1 (- 8 %, - 10 %, and - 11 %, respectively, p < 0.05). Significant decrements were found in MVC post (- 13 %, p < 0.05) and MVC post5 (- 10.5 %, p < 0.05) compared to MVC pre. The RMS value of VL muscle increased significantly after sprints (RMS pre vs. RMS post: + 15 %, p < 0.05). Values of MF decreased significantly in both VL and VM after sprints. In conclusion, our results indicate that the increase in quadriceps EMG amplitude following high-intensity intermittent short sprints was not sufficient to maintain the required force output. The concomitant decrease in frequency components would suggest a modification in the pattern of muscle fiber recruitment, and a decrease in conduction velocity of active fibers.

Effect of inertia on performance and fatigue pattern during repeated cycle sprints in males and females.

The effect of recovery duration on performance and fatigue pattern during short exercises was studied including and excluding the flywheel inertia. Subjects (11 males and 11 females) performed a force-velocity test to determine their optimal force (f (opt)). On the following day, subjects performed randomly 4 series of two 8-s sprints against f (opt), with 15 s (R (15)), 30 s (R (30)), 60 s (R (60)), and 120 s (R (120)) recovery between sprints. The cycle (Monark 824 E, Stockholm, Sweden) was equipped with an optical sensor to calculate the revolution velocity of the pedal. For each sprint, peak power (P (peak)), mechanical work (W) and time to reach P (peak) (t (Ppeak)) were calculated including (I) and excluding (NI) the acceleration of the flywheel. For a given sprint, P (peak) and W were greater and t (Ppeak) was lower in I compared to NI condition (p < 0.05). Differences averaged 13 % for P (peak), 20 % for W, 34 % for t (Ppeak), and remained constant between sprints 1 and 2. In sprint 2, P (peak) and W were significantly reduced compared to sprint 1 only after R (15) and R (30) in I and NI (p < 0.05), and no gender differences occurred. In each sprint, P (peak) and W were higher (p < 0.001) and t (Ppeak) was shorter (p < 0.05) in males than in females, and gender differences were the same including or excluding the flywheel inertia. In conclusion, values excluding inertia underestimated mechanical performance and consequently the total energy supply. However, the pattern of fatigue and gender differences in performance and fatigue remained unchanged whatever the condition (I or NI). This result may have practical implications when the flywheel inertia can not be taken into account in the calculation of mechanical work and power output.