Mental fatigue does not affect maximal anaerobic exercise performance

Purpose

Mental fatigue can negatively impact on submaximal endurance exercise and has been attributed to changes in perceived exertion rather than changes in physiological variables. The impact of mental fatigue on maximal anaerobic performance is, however, unclear. Therefore, the aim of the present study was to induce a state of mental fatigue to examine the effects on performance, physiological and perceptual variables from subsequent tests of power, strength and anaerobic capacity.

Methods

Twelve participants took part in the single-blind, randomised, crossover design study. Mental fatigue was induced by 90 min of the computer-based Continuous Performance Task AX version. Control treatment consisted of 90 min of watching emotionally neutral documentaries. Participants consequently completed countermovement jump, isometric leg extension and a 3-min all-out cycling tests.

Results

Results of repeated measures analysis of variance and paired t tests revealed no difference in any performance or physiological variable. Rating of perceived exertion tended to be greater when mentally fatigued (mental fatigue = 19 ± 1 vs control = 18 ± 1, p = 0.096, \(\eta^{2}_{\text{p}}\) = .232) and intrinsic motivation reduced (mental fatigue = 11 ± 4 vs control = 13 ± 6, p = 0.063, d = 0.597) in the mental fatigue condition.

Conclusions

Near identical responses in performance and physiological parameters between mental fatigue and control conditions suggest that peripheral mechanisms primarily regulate maximal anaerobic exercise. Whereas mental fatigue can negatively impact submaximal endurance exercise, it appears that explosive power, voluntary maximal strength and anaerobic work capacity are unaffected.

     

Influence of age on blood pressure recovery after maximal effort ergometer exercise in non-athletic adult males

This study investigated whether age influences blood pressure recovery after maximal exercise in adult males. Forty healthy, non-athletic adult males (20 young, aged 22 ± 3.46 years and 20 older, aged 48 ± 6.91 years) participated in the study. Subjects performed a maximal-effort ergometer exercise test. Peak oxygen uptake (VO_2max) was measured during the exercise protocol; heart rate (HR) and blood pressure (BP) were measured before exercise, during exercise (at 2-min intervals), and at the first minute of post-exercise recovery and subsequently at 2-min intervals until the recovery of BP. Results indicated that young adults had lower systolic blood pressure (SBP) recovery ratio (P < 0.05), lower SBP recovery time (P < 0.001), higher SBP% decline in 1, and 3 min (P < 0.001), and higher DBP% decline in 1, and 3 min (P < 0.05, <0.001) than the older adults, thus indicating faster BP recovery in young than older adults. A bivariate correlation test, revealed significant associations (P < 0.001, <0.01) between age and BP recovery parameters: percentage SBP decline in 1 and 3 min (27 and 39%), percentage DBP decline in 1 and 3 min (14 and 26%), third minute SBP ratio (22%), and SBP recovery time (72%). After controlling for factors affecting BP recovery such as resting SBP, percentage HR decline, VO_2max and delta SBP, the observed correlations reduced in SBP recovery time (29%; P < 0.002) but disappeared (P > 0.01) in the other BP recovery parameters. These data indicate the need to take into account, factors affecting BP recovery when interpreting the effect of age on BP responses after exercise in future investigations.     

Sodium citrate ingestion and its effects on maximal anaerobic exercise of different durations

Summary The effects of an alkalising agent were studied in ten subjects who participated in anaerobic testing on a cycle ergometer to determine the effectiveness of sodium citrate (0.5 g·kg^–1 body mass) as an ergogenic aid during exercise of 10-s, 30-s, 120-s and 240-s duration. Blood was collected prior to, after ingestion of sodium citrate (NaHCO₃), and postexercise, from a heated (43–46°C) fingertip and analysed immediately postcollection for pH, partial pressure of oxygen and carbon dioxide, base excess and blood bicarbonate. Total work undertaken (kJ) and peak power (W) achieved during the tests was also obtained via a work monitor unit. The results indicated that a dose of 0.5 g sdkg^–1 body mass sodium citrate had no ergogenic benefit for exercise of either 10-s or 30-s duration. Blood bicarbonate concentrations, however, were significantly increased (P<0.05) following ingestion of the citrate during these trials. Exercise periods of 120 s and 240 s were significantly increased (P<0.05) above the control and placebo conditions following sodium citrate ingestion. Blood bicarbonate concentrations were again increased above control and placebo conditions and blood lactate concentrations were also increased following the citrate trials. The pH decreased significantly (P<0.05) in all trials below the control and placebo conditions. On the basis of the exercise undertaken in this study we would suggest that a dose of 0.5 g·kg^–1 body mass of sodium citrate could improve anaerobic exercise performance of 120-s and 240-s duration.     

Modelling of aerobic and anaerobic energy production during exhaustive exercise on a cycle ergometer

An extension of the original hyperbolic model (Model-2) was proposed by using power output required to elicit maximal oxygen uptake (P _t). This study aimed to test this new model (Model-α) using mechanical work produced during cycle ergometry. Model α assumed that power exceeding a critical power (P _c) was met partly by the anaerobic metabolism. The parameter α was the proportion of the power exceeding P _c provided by anaerobic metabolism, while power exceeding P _t was exclusively met by anaerobic metabolism. Aerobic power was assumed to rise monoexponentially with a time constant τ. The exhaustion was assumed to be reached when the anaerobic work capacity W′ was entirely utilised. Twelve subjects performed one progressive ramp test to assess the power at ventilatory threshold (P _VT) and P _t and five constant-load exercise to exhaustion within 2–30 min, with one to estimate the maximal accumulated oxygen deficit (MAOD). Parameters from Model α were fitted with τ equal to 0, 10, 20 and 30 s. Results in goodness-of-fit was better than Model-2 whatever the value assumed for τ (P < 0.05). The value of τ did not affect much the estimates for P _c and α. P _c estimates were significantly correlated with P _c from Model-2 and with P _VT. W′ estimates, which were dependent on the value ascribed to τ, were not statistically different than MAOD. These two variables were, however, not significantly correlated. In conclusion, Model α could provide useful information on the critical power and the anaerobic contribution according to exercise intensity, whereas W′ estimates should be used with care because of the sensitivity to the assumption on aerobic power kinetics τ.     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Muscle function during brief maximal exercise: accurate measurements on a friction-loaded cycle ergometer

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N·kg^–1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137–180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17–214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (v _opt) and individual maximal power output (P _max) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since v _opt has been demonstrated to be related to human fibre type composition both v _opt, P _max and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.     

Ultra short-term heart rate recovery after maximal exercise in continuous versus intermittent endurance athletes

This study tested the hypothesis that athletes participating in intermittent sports would exhibit a faster heart rate recovery (HRR) during the initial phase (<30 s) following maximal exercise than athletes participating in continuous endurance sports. Forty-six male athletes were allocated into continuous (CNT, n = 24) or intermittent groups (INT, n = 22), matched for age and aerobic fitness. Athletes performed maximal exercise on a treadmill using the ramp protocol. Immediately upon exercise cessation, subjects were placed supine with continuous measurement of HR during the first minute of recovery. Data were analyzed in 10-s intervals and compared between the groups. Repeated measures ANOVA showed a group × time interaction effects (p ≤ 0.01) for HRR expressed in both beats min⁻¹ and in percentage of peak post-exercise HR (% HR_peak). The INT group had lower HR than CNT group at 10 s (189 vs. 192 beats min⁻¹, p = 0.04; and 96.3 vs. 97.9% HR_peak, p = 0.009) and 20 s (184 vs. 188 beats min⁻¹, p = 0.049; and 93.6 vs. 95.7% HR_peak, p = 0.021) intervals of recovery. The results suggest that athletes engaged in intermittent sports are likely to have faster HRR during the first 20 s after maximal exercise than their counterparts trained for continuous performance.     

Effect of caffeine ingestion after creatine supplementation on intermittent high-intensity sprint performance

The aim of this study was to investigate the effects of acute caffeine ingestion on intermittent high-intensity sprint performance after 5 days of creatine loading. After completing a control trial (no ergogenic aids, CON), twelve physically active men were administered in a double-blind, randomized crossover protocol to receive CRE + PLA (0.3 g kg⁻¹ day⁻¹ of creatine for 5 days then followed by 6 mg kg⁻¹ of placebo) and CRE + CAF (0.3 g kg⁻¹ day⁻¹ of creatine for 5 days and followed by 6 mg kg⁻¹ of caffeine), after which they performed a repeated sprint test. Each test consisted of six 10-s intermittent high-intensity sprints on a cycling ergometer, with 60-s rest intervals between sprints. Mean power, peak power, rating of perceived exertion (RPE), and heart rates were measured during the test. Blood samples for lactate, glucose, and catecholamine concentrations were drawn at specified intervals. The mean and peak power observed in the CRE + CAF were significantly higher than those found in the CON during Sprints 1 and 3; and the CRE + CAF showed significantly higher mean and peak power than that in the CRE + PLA during Sprints 1 and 2. The mean and peak power during Sprint 3 in the CRE + PLA was significantly greater than that in the CON. Heart rates, plasma lactate, and glucose increased significantly with CRE + CAF during most sprints. No significant differences were observed in the RPE among the three trials. The present study determined that caffeine ingestion after creatine supplements augmented intermittent high-intensity sprint performance.     

Dynamics of anaerobic and aerobic energy supplies during sustained high intensity exercise on cycle ergometer

Eight male subjects were examined for the transition from anaerobic to aerobic energy supplies during supramaximal pedalling for 120s on a cycle ergometer. The O₂ debt and O₂ deficit were measured for anaerobic supply, while O₂ intake during exercise was measured for aerobic supply. The lactic acid system was also observed through postexercise peak blood lactate concentration [la^–]_b,peak. Since a continuous observation of O₂ debt and [la^–]_b,peak during a single period of pedalling is not possible, pedalling of seven varying durations (5,15,30,45,60,90 and 120 s) were repeated. Mechanical power output reached its peak immediately after the beginning of exercise, then rapidly declined, becoming gradual after 60 s. The O₂ debt and O₂ deficit were highest immediately after the beginning of exercise, then rapidly decreased to nil in 60 s. The 0₂ intake was small at the beginning, then rapidly increased to attain a steady state in 30 s at 80%–90% of the maximal 02 intake of the subject. Energy supply from the lactic acid system indicated by the increment in [la^–]_b,peak reached its highest value during the period between 5 and 15 s, then rapidly decreased to nil in 60 s. The results would suggest that anaerobic supply was the principal contributor during the initial stage of exercise, but that aerobic supply gradually took over. In 60 s anaerobic supply ceased, and aerobic supply became the principal contributor. The cessation of anaerobic energy supply took place much sooner than the 2 min that is conventionally suggested.     

Force-velocity relationship and maximal power on a cycle ergometer

Summary The force-velocity relationship on a Monark ergometer and the vertical jump height have been studied in 152 subjects practicing different athletic activities (sprint and endurance running, cycling on track and/or road, soccer, rugby, tennis and hockey) at an average or an elite level. There was an approximatly linear relationship between braking force and peak velocity for velocities between 100 and 200 rev · min⁻¹. The highest indices of force P₀, velocity V₀ and maximal anaerobic power (W_max) were observed in the power athletes. There was a significant relationship between vertical jump height and W_max related to body mass.     

Effects of bicarbonate ingestion on the respiratory compensation threshold and maximal exercise performance

Six males performed cycle ergometer exercise on two occasions in random order. Each exercise was preceded by a 2-h period in which matched capsules were administered orally, containing either starch (C) or NaHCO3 (E) in a dose of a 0.2 g.kg-1 body wt; pre-exercise blood pH and [HCO3-] were 7.34 +/- 0.01 and 23.7 +/- 0.5 mM (mean +/- S.E.) for the C study, and 7.41 +/- 0.01 and 28.6 +/- 1.3 mM for the E study (p less than 0.001 and p less than 0.01, respectively). Exercise was continuous and maintained for 10 min at 40% of maximal oxygen uptake (40% VO2max), followed by 15 min at 12 W above the respiratory compensation threshold ([+RCT]) which was determined by the increase of the ventilatory equivalent for carbon dioxide (VE.VCO2(-1)), and for as long as possible at 95% VO2max. Endurance time at 95% VO2max was significantly longer in E than in C (2.98 +/- 0.64 min vs. 2.00 +/- 0.44 min, p less than 0.05). The rate of increase in arterialized venous lactate (LA) was higher in E than in C from rest to exercise at [+RCT], while there was no significant difference in the hydrogen ions ([H+]). Consequently, [H+].LA-1 (nM.mM-1) was significantly lower in E than in C. The change of VE.VCO2(-1) was shifted downward in E compared to C during exercise with the lowest value being observed at the same exercise stage. These results suggest that the respiratory responses to exercise are not affected by the higher level of [HCO3-] induced by NaHCO3 ingestion, and appear to reflect the net change of plasma [HCO3-] or [H+]. Also, induced metabolic acidosis has little effect on [H+] appearance in blood.     

The effect of sodium bicarbonate and sodium citrate ingestion on anaerobic power during intermittent exercise

Summary The effect of sodium bicarbonate and sodium citrate ingestion on cycling performance in three 30 s Wingate Anaerobic Tests separated by 6 min recovery periods has been studied using 6 male subjects. Subjects ingested either sodium bicarbonate (B), sodium bicarbonate plus sodium citrate (BC), sodium citrate (C) or sodium chloride (P) 2.5 h prior to exercise in a dose of 0.3 g kg⁻¹ body weight. Pre-exercise blood pH was 7.44±0.06, 7.42±0.05, 7.41±0.05 and 7.38±0.04 in the C, BC, B and P conditions respectively. Mean and peak power output were significantly reduced by successive Wingate tests but not significantly affected by the treatments. Performance in the second and third tests was highest following C, BC and B ingestion. The total work done in the 3 tests was 103%, 102% and 101% of that achieved in the P condition after C, BC and B ingestion respectively. The increased alkali reserve recorded subsequent to bicarbonate and citrate treatment reduced mean post-exercise acidosis, although pH was significantly higher only in the C condition (p<0.05) compared to P after each exercise bout. No significant differences in plasma lactate concentration were recorded at any time. Citrate ingestion appears to be most effective in elevating blood pH and [HCO₃ ⁻], and in enhancing performance in short-term intermittent exercise. This study demonstrates that alkali ingestion results in significant shifts in the acid-base balance of the blood and has a small, but non-significant, effect on anaerobic power and capacity as measured in a series of 3 Wingate Anaerobic Tests.     

The effects of exercise-induced muscle damage on maximal intensity intermittent exercise performance

Exercise-induced muscle damage (EIMD) is a common occurrence following activities with a high eccentric component. Alterations to the torque–velocity relationship following EIMD would appear to have serious implications for athletic performance, particularly as they relate to impairment of maximal intensity exercise. However, this has been studied infrequently. The purpose of this study was to assess the effects of EIMD on maximal intermittent sprint performance. Ten male participants (age 22.4±3.2 years, height 178.6±5.2 cm, mass 80.6±10.7 kg) performed 10×6 s cycle ergometer sprints, interspersed with 24 s recovery against a load corresponding to 0.10 kp/kg and 10×10 m sprints from a standing start, each with 12 s active (walking) recovery. All variables were measured immediately before and at 30 min, 24, 48 and 72 h following a plyometric exercise protocol comprising of 10×10 maximal counter movement jumps. Repeated measures ANOVA showed significant changes over time (all P<0.05) for perceived soreness, plasma creatine kinase activity (CK), peak power output (PPO), sprint time and rate of fatigue. Soreness was significantly higher (P<0.01) than baseline values at all time intervals (3.1, 4.9, 5.5 and 3.2 at 30 min, 24, 48 and 72 h, respectively). CK was significantly elevated (P<0.05) at 24 h (239 IU/l) and 48 h (245 IU/l) compared to baseline (151 IU/l). PPO was significantly lower (P<0.05) than baseline (1,054 W) at all time intervals (888, 946, 852 and 895 W, at 30 min, 24, 48 and 72 h, respectively). The rate of fatigue over the ten cycling sprints was reduced compared to baseline, with the greatest reduction of 48% occurring at 48 h (P<0.01). This was largely attributed to the lower PPO in the initial repetitions, resulting in a lower starting point for the rate of fatigue. Values returned to normal at 72 h. Sprint times over 10 m were higher (P<0.05) at 30 min, 24 h and 48 h compared to baseline (1.96 s) with values corresponding to 2.01, 2.02 and 2.01 at 30 min, 24 h and 48 h, respectively. Values returned to baseline by 72 h. The results provide further evidence that, following a plyometric, muscle-damaging exercise protocol, the ability of the muscle to generate power is reduced for at least 3 days. This is also manifested by a small, but statistically significant reduction in very short-term (2 s) intermittent sprint running performance. These findings have implications for appropriate training strategies in multiple sprint sports.     

Impact of the exercise mode on heart rate recovery after maximal exercise

Heart rate recovery 1 min after exercise termination (HRR-1) is a prognostic predictor. However, the influence of the exercise mode on HRR-1 is incompletely characterised. Twenty-nine young and healthy subjects and 16 elderly patients with chronic heart failure underwent cardiopulmonary exercise testing using cycle ergometer and treadmill ramp protocols in random order. HRR-1 and heart rate recovery 2 and 3 min after exercise (HRR-2, HRR-3) during active recovery and peak oxygen consumption (peak VO₂) were measured. In both healthy subjects (32 ± 14 vs. 27 ± 10 bpm) and HF patients (19 ± 8 vs. 14 ± 9 bpm), HRR-1 was faster after cycle exercise (p = 0.029; p for between group difference 0.94). In contrast, HRR-2 and HRR-3 were similar after both tests in both groups. Peak VO₂ was lower during cycle as compared to treadmill exercise in both groups. In conclusion, in both healthy subjects and HF patients, HRR-1 depends on the mode of exercise as peak VO₂ does.     

Effects of prolonged warm-up exercise above and below anaerobic threshold on maximal performance

Summary The purpose of the present study was to determine the effects of prolonged warm-up exercise above and below anaerobic threshold (AT) on maximal performance. Warm-up exercise consisted of pedalling the Monark cycle ergometer at either 40% (Below AT) or 68% (Above AT) of VO₂ max for 60 min. Each maximal performance consisted of two 40 s bouts of all out pedalling on the Monark cycle ergometer against 5.5 kg resistance separated by a 5 min rest period. These tests were administered on two occasions without warm-up exercise and were found to be reproducible for work output and peak blood lactate concentration. Below AT warm-up exercise significantly increased core temperature with no increase in steady state blood lactate concentration and was thus representative of a desired warmed-up status. This condition did not contribute to an improved maximal performance. Above AT warm-up exercise resulted in significant increases in core temperature and steady state blood lactate concentration. Work output and peak blood lactate concentration for maximal exercise were significantly decreased. It was concluded that task specific prolonged warm-up exercise below AT does not contribute to an improved maximal performance of the type employed in the present study. Following warm-up exercise above AT, maximal performance was impaired. This was attributed to probable glycogen depletion in fast twitch muscle fibers which in turn may have contributed to a decreased lactate production.This research was supported by the Graduate Research Council of the University of Louisville     

The influence of maximal aerobic power on recovery of skeletal muscle following anaerobic exercise

Phosphorus magnetic resonance spectroscopy (³¹P-MRS) was used to investigate the influence of maximal aerobic power (˙VO _2max) on the recovery of human calf muscle from high-intensity exercise. The (˙VOO_2max) of 21 males was measured during treadmill exercise and subjects were assigned to either a low-aerobic-power (LAP) group (n?=?10) or a high-aerobic-power (HAP) group (n?=?11). Mean (SE) ˙VO _2max of the groups were 46.6 (1.1) and 64.4 (1.4) ml?·?kg^?1?·?min^?1, respectively. A calf ergometry work capacity test was used to assign the same relative exercise intensity to each subject for the MRS protocol. At least 48 h later, subjects performed the rest (4 min), exercise (2 min) and recovery (10 min) protocol in a 1.5 T MRS scanner. The relative concentration of phosphocreatine (PCr) was measured throughout the protocol and intracellular pH (pH_i) was determined from the chemical shift between inorganic phospate (P_i) and PCr. End-exercise PCr levels were 27 (3.4) and 25 (3.5)% of resting levels for LAP and HAP respectively. Mean resting pH_i was 7.07 for both groups, and following exercise it fell to 6.45 (0.04) for HAP and 6.38 (0.04) for LAP. Analysis of data using non-linear regression models showed no differences in the rate of either PCr or pH_i recovery. The results suggest that ˙VO_2max is a poor predictor of metabolic recovery rate from high-intensity exercise. Differences in recovery rate observed between individuals with similar ˙VO_2max imply that other factors influence recovery.     

High level of skeletal muscle carnosine contributes to the latter half of exercise performance during 30-s maximal cycle ergometer sprinting

The histidine-containing dipeptide carnosine (beta-alanyl-L-histidine) has been shown to significantly contribute to the physicochemical buffering in skeletal muscles, which maintains acid-base balance when a large quantity of H(+) is produced in association with lactic acid accumulation during high-intensity exercise. The purpose of the present study was to examine the relations among the skeletal muscle carnosine concentration, fiber-type distribution, and high-intensity exercise performance. The subjects were 11 healthy men. Muscle biopsy samples were taken from the vastus lateralis at rest. The carnosine concentration was determined by the use of an amino acid autoanalyzer. The fiber-type distribution was determined by the staining intensity of myosin adenosinetriphosphatase. The high-intensity exercise performance was assessed by the use of 30-s maximal cycle ergometer sprinting. A significant correlation was demonstrated between the carnosine concentration and the type IIX fiber composition (r=0.646, p<0.05). The carnosine concentration was significantly correlated with the mean power per body mass (r=0.785, p<0.01) during the 30-s sprinting. When dividing the sprinting into 6 phases (0-5, 6-10, 11-15, 16-20, 21-25, 26-30 s), significant correlations were observed between the carnosine concentration and the mean power per body mass of the final 2 phases (21-25 s: r=0.694, p<0.05; 26-30 s: r=0.660, p<0.05). These results indicated that the carnosine concentration could be an important factor in determining the high-intensity exercise performance.     

Effect of muscle glycogen availability on maximal exercise performance

This investigation determined the influence of pre-exercise muscle glycogen availability on performance during high intensity exercise. Nine trained male cyclists were studied during 75 s of all-out exercise on an air-braked cycle ergometer following muscle glycogen-lowering exercise and consumption of diets (energy content approximately 14 MJ) that were either high (HCHO – 80% CHO) or low (LCHO – 25% CHO) in carbohydrate content. The exercise-diet regimen was successful in producing differences in pre-exercise muscle glycogen contents [HCHO: 578(SEM?55) mmol?·?kg^?1 dry mass; LCHO: 364 (SEM 58) P??1 dry mass]. Despite this difference in muscle glycogen availability, there were no between trial differences for peak power [HCHO 1185 (SEM 50)W, LCHO 1179 (SEM?48)W], mean power [HCHO 547 (SEM?5)W, LCHO 554 (SEM ?8)W] and maximal accumulated oxygen deficit [HCHO 54.4 (SEM?2.3)?ml?·?kg^?1, LCHO 54.6 (SEM?2.0) ml?·?kg^?1]. Postexercise muscle lactate contents (HCHO 95.9 (SEM?4.6)?mmol?·?kg^?1 dry mass, LCHO 82.7 (SEM?12.3) mmol?·?kg^?1 dry mass, n?=?8] were no different between the two trials, nor were venous blood lactate concentrations immediately after and during recovery from exercise. These results would indicate that increased muscle glycogen availability has no direct effect on performance during all-out high intensity exercise.     

No effect of prior caffeine ingestion on neuromuscular recovery after maximal fatiguing contractions

The purpose of this study was to test the hypothesis that prior caffeine ingestion would enhance neural recovery after isometric fatiguing maximal intermittent plantar flexions, and thus would enhance the recovery of voluntary muscle strength. After a familiarisation session, 13 males randomly participated in two experimental trials where they ingested either caffeine (~6 mg/kg) or identical placebo pills 1 h prior to testing. Subjects were tested for electromyogram (EMG) activity and evoked V-waves in the soleus and gastrocnemius medialis muscles. These measurements were obtained during brief plantar flexion maximum voluntary isometric contractions (MVICs), and normalised by the superimposed maximal M-wave (EMG/M_SUP and V/M_SUP, respectively), before and after (20 s, 10 min and 20 min) a fatigue protocol (seven 25 s MVICs, 5 s rest). There were no effects (P > 0.05) of caffeine ingestion on EMG/M_SUP, V/M_SUP, MVIC or M_SUP. The central neural modulation (EMG/M_SUP and V/M_SUP) and voluntary strength changes followed a similar time-course with a substantial reduction 20 s post-fatigue and a gradual return towards baseline values.     

Relationship between muscle fatigue and oxygen uptake during cycle ergometer exercise with different ramp slope increments

Summary The surface electromyogram (EMG) from active muscle and oxygen uptake ( ) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W · min^–1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMG_bp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake ( ) and the iEMG_bp between 10 and 30, and 10 and 40 W · min –1 ramp exercises (P < 0.05). However, no significant differences were obtained in and corresponding to the iEMG_bp during the four ramp exercises. With respect to the relationship between and exercise intensity during the ramp increments, the -exercise intensity slope showed significant differences only for the upper half (i.e. above iEMG_bp). These results demonstrated that the and at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to and the iEMG_bp was varied by the change of ramp slopes. In addition, the significant differences in the exercise intensity slopes for the upper half of the tests would suggest that the recruitment patterns of MU and/or muscle metabolic state might be considerably altered depending upon the ramp slope increments.