Workload Trials Research Articles

Comparison of two different cooling systems in alleviating thermal and physiological strain during prolonged exercise in the heat

This study compared the efficacy of an ice vest comprising of water (WATER) or a water-carbon (CARBON) emulsion on thermophysiological responses to strenuous exercise in the heat. Twelve male cyclists completed three 50-minute constant workload trials (55% of peak power output, ambient temperature 30.4 ± 0.6°C) with WATER, CARBON, and without ice vest (CONTROL), respectively. The increase in core body temperature (Tcore) was lower in WATER at 40 (−0.49 ± 0.34 °C) and 50 minutes (−0.48 ± 0.48 °C) and in CARBON at 30 (−0.41 ± 0.48 °C), 40 (−0.54 ± 0.51 °C), and 50 minutes (−0.67 ± 0.62 °C) as compared to CONTROL (p < 0.05, ES > 0.8). While heart rate and blood lactate kinetics did not differ between the conditions, statistical main effects in favour of both WATER and CARBON were found for thermal sensation (condition p < 0.001 and interaction p < 0.01) and rating of perceived exertion (condition p < 0.05). Per-cooling with CARBON and WATER similarly reduced Tcore but not physiological strain during prolonged exercise in the heat. Practitioner Summary: Exercise in the heat is characterised by increases in thermophysiological strain. Both per-cooling with a novel carbon-based and a conventional water-based ice vest were shown to reduce core temperature significantly. However, due to its lower mass, the carbon-based system may be recommended especially for weight-bearing sports.

Combination of aerobic exercise and an arginine, alanine, and phenylalanine mixture increases fat mobilization and ketone body synthesis.

During exercise, blood levels of several hormones increase acutely. We hypothesized that consumption of a specific combination of amino acids (arginine, alanine, and phenylalanine; A-mix) may be involved in secretion of glucagon, and when combined with exercise may promote fat catabolism. Ten healthy male volunteers were randomized in a crossover study to ingest either A-mix (3g/dose) or placebo (3g of dextrin/dose). Thirty minutes after ingesting, each condition subsequently performed workload trials on a cycle ergometer at 50% of maximal oxygen consumption for 1h. After oral intake of A-mix, the concentrations of plasma ketone bodies and adrenalin during and post-exercise were significantly increased. The area under the curve for glycerol and glucagon was significantly increased in the post-exercise by A-mix administration. These results suggest that pre-exercise ingestion of A-mix causes a shift of energy source from carbohydrate to fat combustion by increasing secretion of adrenalin and glucagon.

The effects of phenylalanine on exercise-induced fat oxidation: a preliminary, double-blind, placebo-controlled, crossover trial

BackgroundWhen combined with exercise, dietary amino acid (AA) supplementation is an effective method for accelerating fat mobilization. However, the effects of single AAs combined with exercise on fat oxidation remains unclear. We hypothesized that consumption of a specific amino acid, L- phenylalanine, may result in the secretion of glucagon, and when combined with exercise may promote fat oxidation.MethodsSix healthy, active male volunteers were randomized in a crossover study to ingest either phenylalanine (3 g/dose) or placebo. Thirty minutes after ingestion each subject performed workload trials on a cycle ergometer for 1 h at 50% of maximal oxygen consumption.ResultsOral intake of phenylalanine caused a significant increase in the concentrations of plasma glycerol and glucagon during exercise. The respiratory exchange ratio was also decreased significantly following ingestion of phenylalanine.ConclusionThese results suggested that pre-exercise supplementation of phenylalanine may stimulate whole body fat oxidation. No serious or study-related adverse events were observed.Trial registrationUMIN000027502 Registered 26 May 2017. Restrospectively registered.

Investigating the Use of Two Low Cost Eye Tracking Systems for Detecting Pupillary Response to Changes in Mental Workload

Eye tracking technologies are being utilized at increasing rates within industry and research due to the very recent availability of low cost systems. This paper presents results from a study assessing two eye tracking systems, Gazepoint GP3 and Eye Tribe, both of which are available for under $500 and provide streaming gaze and pupil size data. The emphasis of this research was in evaluating the ability of these eye trackers to identify changes in pupil size which occur as a function of variations in lighting conditions as well as those associated with workload. Ten volunteers participated in an experiment in which a digit span task was employed to manipulate workload as user’s fixated on a monitor which varied in background luminance (black, gray and white). Results revealed that both systems were able to significantly differentiate pupil size differences in high and low workload trials and changes due to the monitor’s luminance. These findings are exceedingly promising for human factors researchers, as they open up the opportunity to augment studies with non-obtrusive, streaming measures of mental workload with technologies available for as little as $100.

Three-dimensional kinematics of competitive and recreational cyclists across different workloads during cycling

Although the link between sagittal plane motion and exercise intensity has been highlighted, no study assessed if different workloads lead to changes in three-dimensional cycling kinematics. This study compared three-dimensional joint and segment kinematics between competitive and recreational road cyclists across different workloads. Twenty-four road male cyclists (12 competitive and 12 recreational) underwent an incremental workload test to determine aerobic peak power output. In a following session, cyclists performed four trials at sub-maximal workloads (65, 75, 85 and 95% of their aerobic peak power output) at 90 rpm of pedalling cadence. Mean hip adduction, thigh rotation, shank rotation, pelvis inclination (latero-lateral and anterior–posterior), spine inclination and rotation were computed at the power section of the crank cycle (12 o'clock to 6 o'clock crank positions) using three-dimensional kinematics. Greater lateral spine inclination (p < .01, 5–16%, effect sizes = 0.09–0.25) and larger spine rotation (p < .01, 16–29%, effect sizes = 0.31–0.70) were observed for recreational cyclists than competitive cyclists across workload trials. No differences in segment and joint angles were observed from changes in workload with significant individual effects on spine inclination (p < .01). No workload effects were found in segment angles but differences, although small, existed when comparing competitive road to recreational cyclists. When conducting assessment of joint and segment motions, workload between 65 and 95% of individual cyclists’ peak power output could be used.

Amino Acid Mixture Enriched With Arginine, Alanine, and Phenylalanine Stimulates Fat Metabolism During Exercise.

Although there have been many investigations of the beneficial effects of both exercise and amino acids (AAs), little is known about their combined effects on the single-dose ingestion of AAs for lipid metabolism during exercise. We hypothesize that taking a specific combination of AAs implicated in glucagon secretion during exercise may increase fat metabolism. We recently developed a new mixture, d-AA mixture (D-mix), that contains arginine, alanine, and phenylalanine to investigate fat oxidation. In a double-blind, placebo-controlled crossover study, 10 healthy male volunteers were randomized to ingest either D-mix (3 g/dose) or placebo. Subjects in each condition subsequently performed a physical task that included workload trials on a cycle ergometer at 50% of maximal oxygen consumption for 1 hr. After oral intake of D-mix, maximum serum concentrations of glycerol (9.32 ± 6.29 mg/L and 5.22 ± 2.22 mg/L, respectively; p = .028), free fatty acid level (0.77 ± 0.26 mEq/L and 0.63 ± 0.28 mEq/L, respectively; p = .022), and acetoacetic acid levels (37.9 ± 17.7 μmol/L and 30.3 ± 13.9 μmol/L, respectively; p = .040) were significantly higher than in the placebo groups. The area under the curve for glucagon during recovery was numerically higher than placebo (6.61 ± 1.33 μg/L · min and 6.06 ± 1.23 μg/L · min, respectively; p = .099). These results suggest that preexercise ingestion of D-mix may stimulate fat metabolism. Combined with exercise, the administration of AA mixtures could prove to be a useful nutritional strategy to maximize fat metabolism.

Consumo de oxigênio durante ciclismo na máxima fase estável de lactato sanguíneo até a exaustão: modelo contínuo vs. intermitente

ObjectiveThe aim of this study was to analyse the accumulated oxygen uptake (VO2), as well the maintained time (TMcg) at high levels during a maximal lactate steady state (MLSS) exercise, determined in continuous (MLSScon) and intermittent (MLSSint) modes, until exhaustion. MethodFourteen trained cyclists performed an incremental maximal testing; 2‐5 continuous and 2‐4 intermittent constant workload trials, in order to identify the MLSScon and MLSSint, respectively; two tests until exhaustion (TTE) (continuous and intermittent) were conducted using their respective MLSS workloads. ResultsThe continuous TTE was significantly lower than TTE at intermittent protocol (54.7±10.9 vs. 67.8±14.3min; p=0.001). The VO2 at target workload (VO2cg) was higher at intermittent exercise (p<0.05), at both situations (MLSS and TTE). On the other hand, TMcg and the VO2 accumulated in MLSS workloads (VO2ACcg) were higher during continuous mode (p<0.0001), at both situations. The total VO2 accumulated (VO2ACt) was similar between intermittent and continuous cycling (MLSS: 104.7±8.7L vs. 103.9±41.1L and TTE: 193.8±41.1L vs. 226.4±53.0L, respectively). ConclusionWhen MLSS continuous and intermittent were performed with same duration or until exhaustion, the VO2ACt was similar, although the TMcg and VO2ACcg were smaller during intermittent exercise.

The role of active muscle mass in determining the magnitude of peripheral fatigue during dynamic exercise.

Greater peripheral quadriceps fatigue at the voluntary termination of single-leg knee-extensor exercise (KE), compared with whole-body cycling, has been attributed to confining group III and IV skeletal muscle afferent feedback to a small muscle mass, enabling the central nervous system (CNS) to tolerate greater peripheral fatigue. However, as task specificity and vastly differing systemic challenges may have complicated this interpretation, eight males were studied during constant workload trials to exhaustion at 85% of peak workload during single-leg and double-leg KE. It was hypothesized that because of the smaller muscle mass engaged during single-leg KE, a greater magnitude of peripheral quadriceps fatigue would be present at exhaustion. Vastus lateralis integrated electromyogram (iEMG) signal relative to the first minute of exercise, preexercise to postexercise maximal voluntary contractions (MVCs) of the quadriceps, and twitch-force evoked by supramaximal magnetic femoral nerve stimulation (Qtw,pot) quantified peripheral quadriceps fatigue. Trials performed with single-leg KE (8.1 ± 1.2 min; 45 ± 4 W) resulted in significantly greater peripheral quadriceps fatigue than double-leg KE (10 ± 1.3 min; 83 ± 7 W), as documented by changes in the iEMG signal (147 ± 24 vs. 85 ± 13%), MVC (-25 ± 3 vs. -12 ± 3%), and Qtw,pot (-44 ± 6 vs. -33 ± 7%), for single-leg and double-leg KE, respectively. Therefore, avoiding concerns over task specificity and cardiorespiratory limitations, this study reveals that a reduction in muscle mass permits the development of greater peripheral muscle fatigue and supports the concept that the CNS tolerates a greater magnitude of peripheral fatigue when the source of group III/IV afferent feedback is limited to a small muscle mass.

Patellofemoral and tibiofemoral forces in cyclists and triathletes: effects of saddle height

High compressive load applied to the patellofemoral joint at great knee flexion angle (e.g. >60Âo of flexion), as usually observed in cycling may provide a link between body position on the bicycle and knee joint forces. The aim of the present study was to compare knee joint forces in different saddle heights. Right pedal force and lower limb kinematics were collected for 24 competitive cyclists and triathletes at self-selected preferred, high (-10Âo of knee flexion angle from preferred), low (+10Âo of knee flexion angle from preferred) and optimal (25Âo of knee flexion angle) saddle heights in submaximal pedalling cadence and workload trials (3.45 ± 0.6 W/kg, 90 ± 2 rpm and 163 ± 33 J). Patellofemoral compressive and tibiofemoral anterior-posterior and compressive force were computed by inverse dynamics and compared for different saddle heights via effect sizes. Patellofemoral compressive force (5-13%) and tibiofemoral compressive force (1-7%) were not substantially affected by changes in saddle height. Tibiofemoral anterior shear force decreased at low saddle heights (4-6% of the preferred height) compared to optimal (35%) and high saddle heights (53%). Greater knee flexion angles were observed for lower saddle heights (8-34%). Knee flexion angle was significantly affected by changes in saddle height, which may indicate that using joint kinematics to assess saddle height effects may be useful to anticipate overload in knee joint.

Pode o limiar de fadiga neuromuscular ser determinado por testes curtos e não exaustivos?

The present study determined the neuromuscular fatigue threshold (NFT) using four different time-periods of analysis of the electromyographic signal and compared these estimations with critical power (CP). Fifteen healthy young men (73.6 ± 5.1 kg, 177.8 ± 7.0 cm, 23.4 ± 5.2 years) performed 3-4 different severe constant workload trials until exhaustion on a cycle ergometer with simultaneous SEMG signals acquisition. The obtained data permitted NFT estimation with four different periods of analysis as follows: initial 30s (T30), 1min (T1), 2min (T2) and total time (TT), as well as CP. T30 and T1 were significantly higher than TT and CP and, T2 and TT did not differ between each other, and both were significantly higher than CP. In addition, TT was significantly correlated to CP (0.72; P &lt; 0.05) and to T2 (0.58; P &lt; 0.05). We conclude that NFT overestimates CP, independent of the time-period analysis used for its determination.

Can neuromuscular fatigue threshold be determined by short and non-exhaustive bouts?

The present study determined the neuromuscular fatigue threshold (NFT) using four different time-periods of analysis of the electromyographic signal and compared these estimations with critical power (CP). Fifteen healthy young men (73.6 ± 5.1 kg, 177.8 ± 7.0 cm, 23.4 ± 5.2 years) performed 3-4 different severe constant workload trials until exhaustion on a cycle ergometer with simultaneous SEMG signals acquisition. The obtained data permitted NFT estimation with four different periods of analysis as follows: initial 30s (T30), 1min (T1), 2min (T2) and total time (TT), as well as CP. T30 and T1 were significantly higher than TT and CP and, T2 and TT did not differ between each other, and both were significantly higher than CP. In addition, TT was significantly correlated to CP (0.72; P < 0.05) and to T2 (0.58; P < 0.05). We conclude that NFT overestimates CP, independent of the time-period analysis used for its determination.

L-Ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism

We examined the effects of L-ornithine administration on physical fatigue. In a double-blind, placebo-controlled, 2-way crossover study, 17 healthy volunteers were randomized to L-ornithine (2000 mg/d for 7 days and 6000 mg/d for 1 day as L-ornithine hydrochloride) or placebo for 8 days. The fatigue-inducing physical task consisted of workload trials on a cycle ergometer at fixed workloads for 2 hours on 2 occasions. We found that oral L-ornithine administration promoted lipid metabolism and activated the urea cycle from serum triacylglycerol, ketone bodies, free fatty acids, and blood ammonia level changing. L-ornithine significantly attenuated the subjective feeling of fatigue (measured by visual analog scale at postrecovery) compared with postload (P < .01). Moreover, in female subjects, the subjective feeling of fatigue was significantly lower compared with the placebo group (P < .05). In the physical performance test in female subjects, the decrease in mean speed for 10 seconds maximum pedaling from 0.5- to 3.5-hour trials in the group receiving L-ornithine was smaller than that in the group receiving placebo (P < .05). These results suggest that L-ornithine has an antifatigue effect by increasing the efficiency of energy consumption and promoting the excretion of ammonia. L-ornithine is a free amino acid and is not rich in meats or fish, so it is difficult to obtain amounts of L-ornithine from ordinary meals that would be sufficient to promote the antifatigue effect. We recommend L-ornithine intake as a nutritional supplement in cases of physical fatigue.

Antifatigue effects of coenzyme Q10 during physical fatigue

Objective This study examined the effects of coenzyme Q10 administration on physical fatigue. Methods In a double-blinded, placebo-controlled, three crossover design, 17 healthy volunteers were randomized to oral coenzyme Q10 (100 or 300 mg/d) or placebo administration for 8 d. As a fatigue-inducing physical task, subjects performed workload trials on a bicycle ergometer at fixed workloads twice for 2 h and then rested for 4 h. During the physical tasks, subjects performed non-workload trials with maximum velocity for 10 s at 30 min (30-min trial) after the start of physical tasks and 30 min before the end of the tasks (210-min trial). Results The change in maximum velocity from the 30- to the 210-min trial in the 300-mg coenzyme Q10–administered group was higher than that in the placebo group. In addition, subjective fatigue sensation measured on a visual analog scale in the 300-mg coenzyme Q10–administered group after the fatigue-inducing physical task and recovery period was alleviated when compared with that in the placebo group. Conclusion Oral administration of coenzyme Q10 improved subjective fatigue sensation and physical performance during fatigue-inducing workload trials and might prevent unfavorable conditions as a result of physical fatigue.

Effects of Applephenon ® and ascorbic acid on physical fatigue

Objective We examined the effects of Applephenon ® and ascorbic acid administration on physical fatigue. Methods In a double-blinded, placebo-controlled, three-way crossover design, 18 healthy volunteers were randomized to oral Applephenon ® (1200 mg/d), ascorbic acid (1000 mg/d), or placebo for 8 d. The fatigue-inducing physical task consisted of workload trials on a bicycle ergometer at fixed workloads for 2 h on two occasions. During the test, subjects performed non-workload trials with maximum velocity for 10 s at 30 min (30-min trial) after the start of the test and 30 min before the end of the test (210-min trial). Results The change in maximum velocity between the 30- and 210-min trials was higher in the group given Applephenon ® than in the group given placebo; ascorbic acid had no effect. Conclusion These results suggest that Applephenon ® attenuates physical fatigue, whereas ascorbic acid does not.

Effects of Citric Acid and L-Carnitine on Physical Fatigue

We examined the effects of citric acid and l-carnitine administration on physical fatigue. In a double-blind, placebo-controlled, 3-way crossover study, 18 healthy volunteers were randomized to oral citric acid (2,700 mg/day), l-carnitine (1,000 mg/day), or placebo for 8 days. The fatigue-inducing physical task consisted of workload trials on a cycle ergometer at fixed workloads for 2 h on 2 occasions. Before the physical load, salivary chromogranin A, measured as a physiological stress marker, was lower in the group given citric acid than in the group given placebo. Also, after the physical load, the subjective feeling of fatigue assessed with a visual analogue scale was lower in the citric acid group than in the placebo group. In contrast, l-carnitine had no effect on chromogranin A or subjective fatigue. These results suggest that citric acid reduces physiological stress and attenuates physical fatigue, whereas l-carnitine does not.

Arterial Oxygen Content Influences Exercise Performance via Effects on Limb Fatigue

PURPOSE: It is well known that arterial oxygen content (CaO2) is positively correlated with whole body exercise performance. We previously demonstrated, by comparing the effects of ΔCaO2 at equal exercise work rates and durations, that CaO2 is negatively correlated with peripheral locomotor muscle fatigue. Accordingly, we investigated the role of locomotor muscle fatigue as a determinant of the effects of ΔCaO2, on exercise performance. METHODS: On separate days, 8 healthy, trained males performed four 5 km cycling time trials (TT) [inspired O2 fraction (FIO2) / CaO2 (ml O2·dl blood−1): 0.15/17.6 (TTHYPO); 0.21/20.9 (TTNORM); 0.28/22.6 (TTISO); 1.0/24.4 (TTHYPER)], as well as 3 constant work-load trials (314 ±13 W; FIO2 / CaO2: 0.15/18.2, 0.21/21.3, 1.0/24.5) to the limit of exhaustion. Quadriceps muscle fatigue was assessed via evoking quadriceps twitch force (Qtw) through magnetic stimulation of the femoral nerve (1–100 Hz) pre- and 2.5-min post-exercise. We determined that this method for peripheral locomotor muscle fatigue assessment was highly reproducible within and between days (coefficient of variation <6%) and highly sensitive to small variations in exercise duration at the same work rate. RESULTS: With each increment in CaO2 from hypoxia to hyperoxia, time trial performance (time required to completion and mean power output) was increased significantly (e.g. 483 s / 270 W with TTHYPO vs. 438 s / 349 W with TTHYPER, p <0.05). Despite these wide differences in time trial performance with varying CaO2, the amount of exercise-induced quadriceps fatigue (% ΔQtw) was nearly identical (ΔQtw pre- to post-exercise = −27 to −29%, p = 0.4). During the constant work-load trials, varying CaO2 resulted in a wide range in time to exhaustion (4.5 ±0.4 min in FIO2 0.15 to 19.4 ±3.9 min in FIO2 1.0; p <0.01), however, similar levels of peripheral locomotor muscle fatigue (ΔQtw −26 to −27%, p = 0.8) were observed following exhaustive exercise. CONCLUSIONS: These findings indicate that a certain critical level of peripheral locomotor muscle fatigue is an important regulated variable during exercise which determines the level of motor output and therefore exercise performance, i.e. power output and time to task completion. Thus, we propose that variations in CaO2 and O2 transport to muscle affect time trial performance secondary to the rate of quadriceps fatigue development, which in turn may feed back to higher motor areas of the central nervous system to modulate or titrate motor output so as to prevent “excessive” development of peripheral locomotor muscle fatigue beyond a critical threshold.

Human Responses to a Workload Change

Twenty male students performed three 5-minute trials of a PC-based multi-task which consisted of three independent tasks, i.e., resource management task, system monitoring (vigilance reaction time) task and compensatory tracking task. Participants were instructed to perform only one task (tracking) during the second trial. Tracking task performance, subjective workload, mood scores and physiological parameters (Tissue Blood Volume, Hemodynamics, Systolic Time Intervals, Heart Rate Variability and Skin Potential Level (SPL))were obtained. The task performance was significantly improved and subjective workloads evaluated by NASA-TLX were significantly low in the second trial. SPL measured on the left palm showed a significantly high value in the low workload trial when compared to high workload trials. No other physiological parameter showed such workload related significant changes among the trials. This result suggested that SPL is sensitive to the workload change although that the electrode must be attached to a palm so that it may disturb task performance.