Treadmill Time Trial Research Articles

Influence of graded hypercapnia on endurance exercise performance in healthy humans.

Military and/or emergency services personnel may be required to perform high-intensity physical activity during exposure to elevated inspired carbon dioxide (CO2). Although many of the physiological consequences of hypercapnia are well characterized, the effects of graded increases in inspired CO2 on self-paced endurance performance have not been determined. The aim of this study was to compare the effects of 0%, 2%, and 4% inspired CO2 on 2-mile run performance, as well as physiological and perceptual responses during time trial exercise. Twelve physically active volunteers (peak oxygen uptake = 49 ± 5 mL·kg-1·min-1; 3 women) performed three experimental trials in a randomized, single-blind, crossover manner, breathing 21% oxygen with either 0%, 2%, or 4% CO2. During each trial, participants completed 10 min of walking at ∼40% peak oxygen uptake followed by a self-paced 2-mile treadmill time trial. One participant was unable to complete the 4% CO2 trial due to lightheadedness during the run. Compared with the 0% CO2 trial, run performance was 5 ± 3% and 7 ± 3% slower in the 2% and 4% CO2 trials, respectively (both P < 0.001). Run performance was significantly slower with 4% versus 2% CO2 (P = 0.046). The dose-dependent performance impairments were accompanied by stepwise increases in mean ventilation, despite significant reductions in running speed. Dyspnea and headache were significantly elevated during the 4% CO2 trial compared with both the 0% and 2% trials. Overall, our findings show that graded increases in inspired CO2 impair endurance performance in a stepwise manner in healthy humans.

Effects of theophylline and theobromine on exercise performance and implications for competition sport: A systematic review.

A systematic review was undertaken to evaluate studies on the effects of theophylline and theobromine on exercise performance in normal (healthy) subjects. Theophylline was found to have been studied on eight occasions and theobromine on one, the number of subjects per study ranging from seven to 15. In two exercise investigations, theophylline was superior to placebo at a p < 0.05 level and no different in four including one that was conducted in artificial hypoxia. In a treadmill time trial over 3 km, theobromine was superior to placebo and equal to caffeine, at the <0.05 level. In strength studies, theophylline increased wrist strength in one and showed a slight but not statistically significant increase in limb strength in four of the seven subjects in the other. Theophylline caused adverse effects in six participants. There were no adverse effects in the theobromine investigation. Although the studies showed contradicting results and/or insufficient data to draw solid conclusions, it appears both drugs have potential to enhance performance and could be considered for inclusion on the WADA banned list.

Effects of Unilateral Versus Bilateral Plyometric Training on Endurance Running Performance

The purpose of the study was to investigate the effects of an 11-week unilateral versus bilateral plyometric training intervention on maximal isometric voluntary (MVC) knee extensor torque, countermovement jump height (CMJ), running economy (RE) and 3-km time trial (TT) performance. Twenty-seven recreationally trained endurance runners (12 females and 15 males) were randomly assigned to one of three groups: unilateral plyometric training (UPT; n = 9), bilateral plyometric training (BPT; n = 9) and control (CON; n = 9). RE, VO2max, 3-km treadmill TT, isometric MVC (bilateral and unilateral) and CMJ (bilateral and unilateral) were measured prior to and after 11 weeks of training (UPT and BPT; volume equated, 20-40 minutes, 2-3 days/week). Separate two-way repeated measures ANOVAs were used to assess within and between group differences in RE, VO2max, 3-km TT, maximal isometric knee extensor torque and CMJ. Following 11 weeks of plyometric training there were significant improvements in RE (UPT 5.6%; BPT 4.9%, p &lt; 0.01) and 3-km TT performance (UPT 2.4%; BPT 2.5%, p &lt; 0.01) in addition to CMJ (UPT 12.5%; BPT 14.5%, p &lt; 0.01) and maximal isometric knee extensor torque in the unilateral group (14.0%, p &lt; 0.01). No significant differences in VO2max or anthropometric measures were detected (p &gt; 0.05). No statistically significant differences between training interventions (p &gt; 0.05) were detected in any measure. These data demonstrate that UPT and BPT result in similar improvements in RE and 3-km TT run performance in recreational distance runners.

Effects of Unilateral Versus Bilateral Plyometric Training on Endurance Running Performance

The purpose of the study was to investigate the effects of an 11-week unilateral versus bilateral plyometric training intervention on maximal isometric voluntary (MVC) knee extensor torque, countermovement jump height (CMJ), running economy (RE) and 3-km time trial (TT) performance. Twenty-seven recreationally trained endurance runners (12 females and 15 males) were randomly assigned to one of three groups: unilateral plyometric training (UPT; n = 9), bilateral plyometric training (BPT; n = 9) and control (CON; n = 9). RE, VO2max, 3-km treadmill TT, isometric MVC (bilateral and unilateral) and CMJ (bilateral and unilateral) were measured prior to and after 11 weeks of training (UPT and BPT; volume equated, 20-40 minutes, 2-3 days/week). Separate two-way repeated measures ANOVAs were used to assess within and between group differences in RE, VO2max, 3-km TT, maximal isometric knee extensor torque and CMJ. Following 11 weeks of plyometric training there were significant improvements in RE (UPT 5.6%; BPT 4.9%, p &lt; 0.01) and 3-km TT performance (UPT 2.4%; BPT 2.5%, p &lt; 0.01) in addition to CMJ (UPT 12.5%; BPT 14.5%, p &lt; 0.01) and maximal isometric knee extensor torque in the unilateral group (14.0%, p &lt; 0.01). No significant differences in VO2max or anthropometric measures were detected (p &gt; 0.05). No statistically significant differences between training interventions (p &gt; 0.05) were detected in any measure. These data demonstrate that UPT and BPT result in similar improvements in RE and 3-km TT run performance in recreational distance runners.

Metabolic and performance responses of male runners wearing 3 types of footwear: Nike Vaporfly 4%, Saucony Endorphin racing flats, and their own shoes

PurposeWe compared running economy (RE) and 3-km time-trial (TT) variables of runners wearing Nike Vaporfly 4% (VP4), Saucony Endorphin lightweight racing flats (FLAT), and their habitual running (OWN) footwear. MethodsEighteen male recreational runners (age = 33.5 ± 11.9 year (mean ± SD), peak oxygen uptake (VO2peak) = 55.8 ± 4.4 mL/kg·min) attended 4 sessions approximately 7 days apart. The first session consisted of a VO2peak test to inform subsequent RE speeds set at 60%, 70%, and 80% of the speed eliciting VO2peak. In subsequent sessions, treadmill RE and 3-km TTs were assessed in the 3 footwear conditions in a randomized, counterbalanced crossover design. ResultsOxygen consumption (mL/kg·min) was less in VP4 (from 4.3% to 4.4%, p ≤ 0.002) and FLAT (from 2.7% to 3.4%, p ≤ 0.092) vs. OWN across intensities, with a non-significant difference between VP4 and FLAT (1.0%–1.7%, p ≥ 0.292). Findings related to energy cost (W/kg) and energetics cost of transport (J/kg·m) were comparable. VP4 3-km TT performance (11:07.6 ± 0:56.6 mm:ss) was enhanced vs. OWN by 16.6 s (2.4%, p = 0.005) and vs. FLAT by 13.0 s (1.8%, p = 0.032). The 3-km times between OWN and FLAT (0.5%, p = 0.747) were similar. Most runners (n = 11, 61%) ran their fastest TT in VP4. ConclusionOverall, VP4 improved laboratory-based RE measures in male recreational runners at relative speeds compared to OWN, but the RE improvements in VP4 were not significant vs. FLAT. More runners exhibited better treadmill TT performances in VP4 (61%) vs. FLAT (22%) and OWN (17%). The variability in RE (–10.3% to 13.3%) and TT (–4.7% to 9.3%) improvements suggests that responses to different types of shoes are individualized and warrant further investigation.

Circulating Bone Biomarkers Are Altered Following A Single Bout Of Strenuous Load Carriage Exercise

Military training creates a multi-stressor environment which has been associated with risk of stress fracture. Understanding the acute bone biomarker responses to exercise can provide a model to study how various stressors or interventions affect bone and its adaptation to physical training. PURPOSE: To characterize the effects of a militarily relevant exercise on circulating bone biomarkers. METHODS: 20 Soldiers (18 male, 2 female); age 21.2±0.9 y, performed a 60 min self-paced treadmill time trial at 1% grade while wearing 30% of body weight vest (EX) and a resting control trial (CON) in a randomized, crossover design. Fasted blood samples were collected at 0630 h (AM) and EX or CON trials commenced ~0900 h. Blood samples were collected before (PRE) and after (POST) exercise, and at +1, +2, and +4 h after EX or time-matched during CON. Additionally, fasted samples were collected for the next 3 mornings at 0630 h (AM Day +1 to +3). Parathyroid hormone (PTH), ionized calcium (iCa), osteocalcin (OCN), sclerostin (SOST), C terminal propeptide of type 1 collagen (CTX), N-terminal propeptide of type 1 collagen (P1NP), bone alkaline phosphatase (BAP), and tartrate resistant acid phosphatase (TRAP5b) were assayed and all samples except AM were adjusted for changes in plasma volume from PRE. Data were analyzed using repeated measured ANOVA. Data are mean ± SE. RESULTS: Compared to PRE, PTH was significantly higher (104±32%, p<0.01) and iCa was lower (-2.5±0.8%, p<0.01) at POST during EX but not during CON. OCN was higher at +1 through +4 h than PRE by 15.9±13.0-20.5±12.0% (p<0.01) during EX but unchanged during CON. SOST was elevated by 29.1±14.2% (p<0.01) at POST vs PRE EX but later time points were not different than CON. CTX was elevated vs PRE at +1 h (43.6±22.2%, p<0.01) in EX condition only; later time points were higher (p<0.01) than PRE under both conditions. P1NP, BAP, and TRAP5b were not different from PRE during EX or CON. There were no changes in the AM Day 1-3 samples except OCN was lower than CON on Day +2 and +3. CONCLUSIONS: Consistent with prior reports, iCa decreased and PTH increased immediately post EX. Some markers of bone resorption and OCN were increased post EX. In sum, the temporal pattern of these biomarkers suggest a transient post exercise increase in resorption, but these changes disappear within 24 h after exercise.

Acetazolamide does not alter endurance exercise performance at 3,500-m altitude.

Acetazolamide (AZ) is a medication commonly used to prevent acute mountain sickness (AMS) during rapid ascent to high altitude. However, it is unclear whether AZ use impairs exercise performance; previous literature regarding this topic is equivocal. The purpose of this study was to evaluate the impact of AZ on time-trial (TT) performance during a 30-h exposure to hypobaric hypoxia equivalent to 3,500-m altitude. Ten men [sea-level peak oxygen consumption (VO2peak): 50.8 ± 6.5 mL·kg-1·min-1; body fat %: 20.6 ± 5.2%] completed 2 30-h exposures at 3,500 m. In a crossover study design, subjects were given 500 mg/day of either AZ or a placebo. Exercise testing was completed 2 h and 24 h after ascent and consisted of 15-min steady-state treadmill walking at 40%-45% sea-level VO2peak, followed by a 2-mile self-paced treadmill TT. AMS was assessed after ~12 h and 22 h at 3,500 m. The incidence of AMS decreased from 40% with placebo to 0% with AZ. Oxygen saturation was higher (P < 0.05) in AZ versus placebo trials at the end of the TT after 2 h (85 ± 3% vs. 79 ± 3%) and 24 h (86 ± 3% vs. 81 ± 4%). There was no difference in time to complete 2 miles between AZ and PL after 2 h (20.7 ± 3.2 vs. 22.7 ± 5.0 min, P > 0.05) or 24 h (21.5 ± 3.4 vs. 21.1 ± 2.9 min, P > 0.05) of exposure to altitude. Our results suggest that AZ (500 mg/day) does not negatively impact endurance exercise performance at 3,500 m.NEW & NOTEWORTHY To our knowledge, this is the first study to examine the impact of acetazolamide (500 mg/day) versus placebo on self-paced, peak-effort exercise performance using a short-duration exercise test in a hypobaric hypoxic environment with a repeated-measures design. In the present study, acetazolamide did not impact exercise performance after 2-h or 24-h exposure to 3,500-m simulated altitude.

Short-Term Mediterranean Diet Improves Endurance Exercise Performance: A Randomized-Sequence Crossover Trial

Objective: Healthful dietary patterns have constituents that are known to improve exercise performance, such as antioxidants, nitrates, and alkalizing effects. However, ergogenic effects of such diets have not been evaluated. We hypothesized that a short-term Mediterranean diet results in better exercise performance, as compared to a typical Western diet.Methods: Eleven recreationally active women (n = 7) and men (n = 4) (body mass index, 24.6 ± 3.2 kg/m2; age 28 ± 3 years) were studied in a randomized-sequence crossover study, in which they underwent exercise performance testing on one occasion after 4 days of a Mediterranean diet and on another occasion after 4 days of a Western diet. A 9- to 16-day washout period separated the two trials. Endurance exercise performance was evaluated with a 5-km treadmill time trial. Anaerobic exercise performance tests included a Wingate cycle test, a vertical jump test, and hand grip dynamometry.Results: Five-kilometer run time was 6% ± 3% shorter (faster) in the Mediterranean diet trial than in the Western diet trial (27.09 ± 3.55 vs 28.59 ± 3.21 minutes; p = 0.030) despite similar heart rates (160 ± 5 vs 160 ± 4 beats/min; p = 0.941) and ratings of perceived exertion (14.6 ± 0.5 vs 15.0 ± 0.5; p = 0.356). No differences between the diet conditions were observed for anaerobic exercise tests, including peak and mean power from the Wingate test (both p ≥ 0.05), the vertical jump test (p = 0.19), and the hand grip strength test (p = 0.69).Conclusions: Our findings extend existing evidence of the health benefits of the Mediterranean diet by showing that this diet is also effective for improving endurance exercise performance in as little as 4 days. Further studies are warranted to determine whether a longer-term Mediterranean diet provides greater benefits and whether it might also be beneficial for anaerobic exercise performance and muscle strength and power.

Effects of an increase in intensity during tapering on 1500-m running performance.

We examined the effect of completing the final interval training session during a taper at either (i) race pace (RP) or (ii) faster than RP on 1500-m running performance and neuromuscular performance. Ten trained runners (age, 21.7 ± 3.0 years; height, 182.9 ± 7.0 cm; body mass, 73.4 ± 6.8 kg; and personal best 1500-m time, 4:17.5 ± 0:26.9 min) completed 2 conditions consisting of 7 days of regular training and a 7-day taper, separated by 3 weeks of training. In 1 condition, the taper was prescribed using prediction models based on the practices of elite British middle-distance runners, with the intensity of the final interval session being equal to 1500-m RP. The taper was repeated in the high-intensity (HI) condition, with the exception that the final interval session was completed at 115% of 1500-m RP. A 1500-m treadmill time trial and measures of maximal voluntary contraction (MVC) and rate of force development (RFD) were completed before and after regular training and tapering. Performance was most likely improved after RP (mean ± 90% confidence limits, 10.1 ± 1.6 s), and possibly beneficial after HI (4.2 ± 12.0 s). Both MVC force (p = 0.002) and RFD (p = 0.02) were improved after tapering, without differences between conditions. An RP taper based on the practices of elite middle-distance runners is recommended to improve performance in young, subelite runners. The effect of this strategy with an increase in interval intensity is highly variable and should be implemented with caution.

Protein Supplementation Throughout 10 Weeks of Progressive Run Training Is Not Beneficial for Time Trial Improvement.

Introduction: Protein supplementation is proposed to promote recovery and adaptation following endurance exercise. While prior literature demonstrates improved performance when supplementing protein during or following endurance exercise, chronic supplementation research is limited.Methods: Runners (VO2peak = 53.6 ± 8.9 ml/kg/min) were counter-balanced into a placebo group (PLA; n = 8) or protein group (PRO; n = 9) based on sex and VO2peak, and underwent 10 weeks of progressive endurance training. Prior to training, body composition, blood cell differentials, non-invasive mitochondrial capacity using near-infrared spectroscopy, and a 5 km treadmill time trial (TT) were evaluated. Progressive training then commenced (5–10% increase in weekly volume with a recovery week following 3 weeks of training) whereby PRO supplemented with 25 g of whey protein following workouts and prior to sleep (additional 50 g daily). PLA supplemented similarly with a < 1 g sugar pill per day. Following training, participants were reanalyzed for the aforementioned tests.Results: VO2peak and initial 5 km TT were not significantly different between groups. PRO consumed significantly more dietary protein throughout the training period (PRO = 132 g/d or 2.1 g/kg/day; PLA = 84 g/d or 1.2 g/kg/day). Running volume increased significantly over time, but was not significantly different between groups throughout training. Blood measures were unaltered with training or supplementation. Mitochondrial capacity trended toward improving over time (time p = 0.063) with no difference between groups. PLA increased lean mass 0.7 kg (p < 0.05) while PRO experienced infinitesimal change (−0.1 kg, interaction p = 0.049). PLA improved 5 km TT performance 6.4% (1 min 31 s), while PRO improved only 2.7% (40 s) (interaction p = 0.080).Conclusion: This is the first evidence to suggest long-term protein supplementation during progressive run training is not beneficial for runners.

The Psychophysiological Regulation of Pacing Behaviour and Performance Fatigability During Long-Distance Running with Locomotor Muscle Fatigue and Exercise-Induced Muscle Damage in Highly Trained Runners

BackgroundLocomotor muscle fatigue (LMMF) and exercise-induced muscle damage (EIMD) are common conditions experienced during long-distance running due to the pooled effect of mechanical and metabolic strain on the locomotor muscles. However, little is known about the instant effects of combined LMMF and EIMD on pacing behaviour and performance during the decisive final stages of ‘real-world’ long-distance running events.MethodsTwenty-two highly trained runners (11 females) completed two maximal self-paced 20-km treadmill time trials in a counterbalanced crossover design: (A) in a tapered condition and (B) with LMMF and EIMD. Indicators of muscle damage, muscle metabolic strain, and endocrinological stress were assessed to investigate the physiological effects, and a three-dimensional framework of perceived fatigability was applied to investigate the perceptual effects of running with LMMF and EIMD on performance fatigability.ResultsLMMF and EIMD caused restrictions in work capacity and medium increases in blood leucocyte and neutrophil count, interleukin-6, and cortisol concentrations, collectively constituting a physiological milieu likely not conducive to high performance. LMMF and EIMD further caused large increases in perceived physical strain and large decreases in valence as well as large increases and decreases in action crisis and flow state, respectively.ConclusionsUnder the constraint of amplified physical duress, findings are suggestive of heuristic and rational antecedents in the goal disengagement process. Dynamic changes in physiological and perceptual effects of LMMF and EIMD are hypothesised to underpin the observed alterations in pacing behaviour and performance fatigability during long-distance running. The applied three-dimensional framework provides a more comprehensive understanding of strain-perception-thinking-action coupling in centrally regulated and goal-directed exercise behaviour.

Modelling perception-action coupling in the phenomenological experience of \u201chitting the wall\u201d during long-distance running with exercise-induced muscle damage in highly trained runners

Background“Hitting the wall” (HTW) can be understood as a psychophysiological stress process characterised by (A) discrete and poignant onset, (B) dynamic interplay between physiological, affective, motivational, cognitive, and behavioural systems, and (C) unintended alteration of pace and performance. A preceding companion article investigated the psychophysiological responses to 20-km self-paced treadmill time trials after producing exercise-induced muscle damage (EIMD) via a standardised muscle-lengthening contraction protocol.MethodsA 5-step procedure was applied determining the extent to which the observed data fit the hypothesised cause-effect relationships. Running with EIMD negatively impacts performance fatigability via (A) amplified physiological responses and a non-adaptive distress response and (B) deterioration in perceived fatigability: increase in perceived physical strain precedes decrease in valence, which in turn precedes increase in action crisis, eventually dissolving the initially aspired performance goal.ResultsFirst, haematological indicators of EIMD predicted increased blood cortisol concentration, which in turn predicted increased performance fatigability. Second, perceived physical strain explained 44% of the relationship between haematological indicators of EIMD and valence, which in turn predicted increased action crisis, which in turn predicted increased performance fatigability. The observed data fitted the hypothesised dual-pathway model well with good model-fit indices throughout.ConclusionsThe hypothesised interrelationships between physiological strain, perception, and heuristic and deliberative decision-making processes in self-regulated and goal-directed exercise behaviour were applied, tested, and confirmed: amplified physiological strain and non-adaptive distress response as well as strain-perception-thinking-action coupling impact performance fatigability. The findings provide novel insights into the psychophysiological processes that underpin the phenomenological experience of HTW and alteration in pacing behaviour and performance.

Short-Term Heat Acclimation and Precooling, Independently and Combined, Improve 5-km Time Trial Performance in the Heat.

James, CA, Richardson, AJ, Watt, PW, Willmott, AGB, Gibson, OR, and Maxwell, NS. Short-term heat acclimation and precooling, independently and combined, improve 5-km time trial performance in the heat. J Strength Cond Res 32(5): 1366-1375, 2018-Following heat acclimation (HA), endurance running performance remains impaired in hot vs. temperate conditions. Combining HA with precooling (PC) demonstrates no additive benefit in intermittent sprint, or continuous cycling exercise protocols, during which heat strain may be less severe compared to endurance running. This study investigated the effect of short-term HA (STHA) combined with mixed methods PC, on endurance running performance and directly compared PC and HA. Nine amateur trained runners completed 5-km treadmill time trials (TTs) in the heat (32° C, 60% relative humidity) under 4 conditions; no intervention (CON), PC, short-term HA (5 days-HA) and STHA with PC (HA + PC). Mean (±SD) performance times were; CON 1,476 (173) seconds, PC 1,421 (146) seconds, HA 1,378 (116) seconds and HA + PC 1,373 (121) seconds. This equated to the following improvements versus CON; PC -3.7%, HA -6.6% and HA + PC -7.0%. Statistical differences were only observed between HA and CON (p = 0.004, d = 0.68, 95% CI [-0.27 to 1.63]) however, similar effect sizes were observed for HA + PC vs. CON (d = 0.70, 95% CI [-0.25 to 1.65]), with smaller effects between PC vs. CON (d = 0.34, 95% CI [-0.59 to 1.27]), HA vs. PC (d = 0.33, 95% CI [-0.60 to 1.26]) and HA + PC vs. PC (d = 0.36, 95% CI [-0.57 to 1.29]). Pilot testing revealed a TT typical error of 16 seconds (1.2%). Precooling offered no further benefit to performance in the acclimated individual, despite modest alleviation of physiological strain. Maintenance of running speed in HA + PC, despite reduced physiological strain, may indicate an inappropriate pacing strategy therefore, further familiarization is recommended to optimize a combined strategy. Finally, these data indicate HA, achieved through cycle training, yields a larger ergogenic effect than PC on 5-km running performance in the heat, although PC remains beneficial when HA is not possible.

Effect of Physical Load on Aerobic Exercise Performance during Heat Stress

This study aimed to investigate the effect of increasing external loads on 5-km treadmill time trial (TT) performance in 20°C and 40°C environmental conditions and to construct an ecologically relevant performance prediction decision aid. Twenty-six male and four female volunteers (age, 23.5 ± 6.9 yr; weight, 76.0 ± 8.9 kg; height, 1.75 ± 0.07 m; V˙O2peak, 50.7 ± 4.5 mL·kg·min) participated in a counterbalanced, mixed-model design, with each subject assigned to a load group (20%, 30%, or 50% body mass (BM); n = 10 per group). Volunteers performed three, self-paced 5-km familiarization TT (treadmill) without external load. Each volunteer then performed a 5-km TT in each environment with loads of either 20% (n = 10), 30% (n = 10), or 50% (n = 10) of BM. 1) Loads of (20%, 30%, and 50% of BM) impaired 5-km TT performance compared with that when unloaded (P < 0.05); 2) the time penalties of the 20% and 30% load were <50% load (P < 0.05); 3) in all trials, the addition of heat exposure reduced 5-km TT performance beyond the penalty of load itself (P < 0.05); and 4) the combination of heat and 50% load resulted in a substantial penalty such that continuous work was not sustainable for all of the volunteers. Relative to prediction models using fixed or constant workload exercise trials, an ecologically valid decision aid was developed from self-paced data, in which pace (km·h) can be predicted for individual levels of heat, load, or heat + load in combination.

The Reliability of a Pre-Loaded Treadmill Time-Trial in Moderate Normobaric Hypoxia.

The purpose of this study was to assess the reliability of a pre-loaded 1 500-m treadmill time trial, conducted in moderate normobaric hypoxia. 8 trained runners/triathletes (24±3 years, 73.2±8.1 kg, 182.5±6.5 cm, altitude specific V˙O2max: 52.9±5.5 ml·kg(-1)·min(-1)) completed 3 trials (the first as a familiarisation), involving 2, 15-min running bouts at 45% and 65% V˙O2max, respectively, and a 1 500-m time trial in moderate normobaric hypoxia equivalent to a simulated altitude of 2 500 m (FiO2~15%). Heart rate, arterial oxygen saturation, skeletal muscle and cerebral tissue oxygenation (StO2), expired gas ( V˙O2 and V˙CO2), and ratings of perceived exertion were monitored. Running performance (Trial 1: 352.7±40; Trial 2: 353.9±38.2 s) demonstrated a low CV (0.9%) and high ICC (1). All physiological variables demonstrated a global CV≤4.2%, and ICC≥0.87, with the exception of muscle (CV 10.4%; ICC 0.70) and cerebral (CV 4.1%; ICC 0.82) StO2. These data demonstrate good reliability of the majority of physiological variables and indicate that a pre-loaded 1 500-m time trial conducted in moderate normobaric hypoxia is a highly reliable test of performance.

Treadmill Time-trial Performance of Unacclimatized Lowlanders Following Rapid Ascent to 3500 m or 4050 m

Our group recently published a mathematical model depicting the relationship of the change in cycle ergometer time-trial (TT) performance duration as a function of increasing elevation for unacclimatized lowlanders within their first 8 hrs of exposure to elevations up to 4300 m (Beidleman et al., Med Sci Sports Exerc 2015). Whether the model is generalizable for TT performance assessments using a different mode of exercise (i.e., treadmill) and within the first 48 hrs of exposure is unknown. PURPOSE: Determine if the changes in treadmill TT performance durations of unacclimatized individuals measured both at sea level (SL, 50 m) and either 3500 m or 4050 m can be estimated accurately using the published cycle ergometer TT performance model. METHODS: Forty-three healthy volunteers (35 men and 8 women; mean ± SD; 22 ± 4 yrs, 74.5 ± 12.5 kg; 49.8± 7.3 ml·kg-1·min-1) completed a treadmill TT lasting 8.0-11.2 km both at SL and within the first 48 hr of arrival at either 3500 m (n = 16) or 4050 m (n = 27). The % increase in treadmill TT duration from SL to each elevation was the outcome variable which was, in turn, compared to the results estimated at the identical elevations using the cycle TT model. RESULTS: The % increase in duration for the treadmill TT versus that estimated using the cycle TT model did not differ either at 3500 m (26.7 ± 14.8% versus 28.4 ± 6.9%, p = 0.69) or 4050 m (44.1 ± 17.5% versus 46.8 ± 1.6%, p = 0.42). CONCLUSION: The findings indicate that our published cycle ergometer model accurately estimates % changes for treadmill TT performance of unacclimatized SL residents during their first 48 hrs of exposure to altitudes of 3500 m and 4050 m. Further, the lack of significant difference between the treadmill and cycle TT performance outcomes at these two elevations suggest that the published predictive model can be applied to treadmill exercise. Disclaimer: Author’s views are not official U.S. Army or DoD policy.

Nighttime feeding likely alters morning metabolism but not exercise performance in female athletes.

The timing of morning endurance competition may limit proper pre-race fueling and resulting performance. A nighttime, pre-sleep nutritional strategy could be an alternative method to target the metabolic and hydrating needs of the early morning athlete without compromising sleep or gastrointestinal comfort during exercise. Therefore, the purpose of this investigation was to examine the acute effects of pre-sleep chocolate milk (CM) ingestion on next-morning running performance, metabolism, and hydration status. Twelve competitive female runners and triathletes (age, 30 ± 7 years; peak oxygen consumption, 53 ± 4 mL·kg(-1)·min(-1)) randomly ingested either pre-sleep CM or non-nutritive placebo (PL) ∼30 min before sleep and 7-9 h before a morning exercise trial. Resting metabolic rate (RMR) was assessed prior to exercise. The exercise trial included a warm-up, three 5-min incremental workloads at 55%, 65%, and 75% peak oxygen consumption, and a 10-km treadmill time trial (TT). Physiological responses were assessed prior, during (incremental and TT), and postexercise. Paired t tests and magnitude-based inferences were used to determine treatment differences. TT performances were not different ("most likely trivial" improvement with CM) between conditions (PL: 52.8 ± 8.4 min vs CM: 52.8 ± 8.0 min). RMR was "likely" increased (4.8%) and total carbohydrate oxidation (g·min(-1)) during exercise was "possibly" or likely increased (18.8%, 10.1%, 9.1% for stage 1-3, respectively) with CM versus PL. There were no consistent changes to hydration indices. In conclusion, pre-sleep CM may alter next-morning resting and exercise metabolism to favor carbohydrate oxidation, but effects did not translate to 10-km running performance improvements.

Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat.

We examined whether daily hot water immersion (HWI) after exercise in temperate conditions induces heat acclimation and improves endurance performance in temperate and hot conditions. Seventeen non-heat-acclimatized males performed a 6-day intervention involving a daily treadmill run for 40min at 65% V̇O2max in temperate conditions (18°C) followed immediately by either HWI (N=10; 40°C) or thermoneutral (CON, N=7; 34°C) immersion for 40min. Before and after the 6-day intervention, participants performed a treadmill run for 40min at 65% V̇O2max followed by a 5-km treadmill time trial (TT) in temperate (18°C, 40% humidity) and hot (33°C, 40% humidity) conditions. HWI induced heat acclimation demonstrated by lower resting rectal temperature (Tre , mean, -0.27°C, P<0.01), and final Tre during submaximal exercise in 18°C (-0.28°C, P<0.01) and 33°C (-0.36°C, P<0.01). Skin temperature, Tre at sweating onset and RPE were lower during submaximal exercise in 18°C and 33°C after 6days in HWI (P<0.05). Physiological strain and thermal sensation were also lower during submaximal exercise in 33°C after 6days in HWI (P<0.05). HWI improved TT performance in 33°C (4.9%, P<0.01) but not in 18°C. Thermoregulatory measures and performance did not change in CON. Hot water immersion after exercise on 6days presents a simple, practical, and effective heat acclimation strategy to improve endurance performance in the heat.

Contextualizing Parasympathetic Hyperactivity in Functionally Overreached Athletes With Perceptions of Training Tolerance

Heart-rate variability (HRV) as a measure of autonomic function may increase in response to training interventions leading to increases or decreases in performance, making HRV interpretation difficult in isolation. This study aimed to contextualize changes in HRV with subjective measures of training tolerance. Supine and standing measures of vagally mediated HRV (root-mean-square difference of successive normal RR intervals [RMSSD]) and measures of training tolerance (Daily Analysis of Life Demands for Athletes questionnaire, perception of energy levels, fatigue, and muscle soreness) were recorded daily during 1 wk of light training (LT), 2 wk of heavy training (HT), and 10 d of tapering (T) in 15 male runners/ triathletes. HRV and training tolerance were analyzed as rolling 7-d averages at LT, HT, and T. Performance was assessed after LT, HT, and T with a 5-km treadmill time trial (5TTT). Time to complete the 5TTT likely increased after HT (effect size [ES] ± 90% confidence interval = 0.16 ± 0.06) and then almost certainly decreased after T (ES = -0.34 ± 0.08). Training tolerance worsened after HT (ES ≥ 1.30 ± 0.41) and improved after T (ES ≥ 1.27 ± 0.49). Standing RMSSD very likely increased after HT (ES = 0.62 ± 0.26) and likely remained higher than LT at the completion of T (ES = 0.38 ± 0.21). Changes in supine RMSSD were possible or likely trivial. Vagally mediated HRV during standing increased in response to functional overreaching (indicating potential parasympathetic hyperactivity) and also to improvements in performance. Thus, additional measures such as training tolerance are required to interpret changes in vagally mediated HRV.

Body Mass Changes and Fluid Consumption During an 80.5-km Treadmill Time Trial

Fluid consumption and maintenance of body mass is crucial to exercise performance, particularly during ultraendurance events. The current study aimed to assess body mass change and hydration status during an 80.5-km treadmill time trial (TT). Ultrarunners were recruited to complete 80.5 km on a motorized treadmill within an artificial laboratory environment. Body mass (BM) was determined prior to, at 16.1-km intervals, and on completion of an 80.5-km TT using bioelectrical impedance analysis (BIA). Ad libitum fluid intake was permitted during the trial, and total fluid consumption and gastrointestinal (GI) symptoms were noted throughout. Total fluid intake was 3294.4 ± 1402.9 mL with an average consumption of 386.9 ± 212.2 mL/h. Prerunning BM (72.59 ± 8.48 kg) was reduced throughout the TT. Overall exercise-induced BM loss averaged 2.78 ± 0.94 kg with a 4.01 ± 1.35% decrease over time, although some retention of BM occurred in the latter stages of the TT. Ambient conditions were maintained throughout with no significant fluctuations in temperature (20.8° ± 0.2°C; P > .05) or humidity (35.7 ± 1.3%; P > .05). Average time to completion was 7 hours 28 minutes 9 seconds ± 1 hour 25 minutes 12 seconds at an average speed of 10.8 ± 1.5 km/h. The current study indicates that participants were unable to maintain prerunning BM following the completion of an 80.5-km TT with an average BM loss of 4%. Consensus guidelines state to avoid BM losses of >3%; therefore this emphasizes the importance of optimal hydration strategies in ultraendurance running.