Alpha band oscillations in common synaptic input are explanatory of the complexity of isometric knee extensor muscle torque signals.

We investigated whether the strength of oscillations in common synaptic input was explanatory of knee extensor (KE) torque signal complexity during fresh and fatigued submaximal isometric contractions, in adults aged from 18 to 90 years. The discharge times of motor units were derived from the vastus lateralis muscle of 60 participants using high-density surface EMG, during 20 s isometric KE contractions at 20% of maximal voluntary contraction, performed before and after a fatiguing repeated isometric KE contraction protocol at 60% of maximal voluntary contraction. Within-muscle coherence Z-scores were estimated using frequency-domain coherence analysis, and muscle torque complexity was assessed using multiscale entropy analysis and detrended fluctuation analysis. Alpha band (5-15 Hz) coherence was found to predict 23.1% and 31.4% of the variance in the complexity index under 28-scales (CI-28) and detrended fluctuation analysis α complexity metrics, respectively, during the fresh contractions. Delta, alpha and low beta band coherence were significantly increased due to fatigue. Fatigue-related changes in alpha coherence were significantly predictive of the fatigue-related changes in CI-28 and detrended fluctuation analysis α. The fatigue-related increase in sample entropy from scales 11 to 28 of the multiscale entropy analysis curves was significantly predicted by the increase in the alpha band coherence. Age was not a contributory factor to the fatigue-related changes in within-muscle coherence and torque signal complexity. These findings indicate that the strength of alpha band oscillations in common synaptic input can explain, in part, isometric KE torque signal complexity and the fatigue-related changes in torque signal complexity.

Inter-day reliability of heart rate complexity and variability metrics in healthy highly active younger and older adults.

PURPOSE: To investigate the inter-day reliability of time-domain, frequency-domain, and nonlinear HRV metrics in healthy highly active younger and older adults. The study also assessed the effect of age on the HRV metrics. METHODS: Forty-four older adults (34 M, 10F; 59 ± 5 years; [Formula: see text] = 40.9 ± 7.6 ml kg-1 min-1) and twenty-two younger adults (16 M, 6F; 22 ± 4 years; [Formula: see text] = 47.2 ± 12.8 ml kg-1 min-1) attended the laboratory. Visit one assessed aerobic fitness through an exercise test. In visits two and three, participants completed a 30-min supine RR interval measurement to derive the HRV metrics. RESULTS: The younger group (YG) and older group (OG) demonstrated poor to good day-to-day relative and absolute reliability for all HRV metrics (OG, ICCs = 0.33 to 0.69 and between day CVs = 3.8 to 29.2%; YG, ICCs = 0.37 to 0.93 and between day CVs = 3.5 to 36.5%). There was a significant reduction in ApEn (P < 0.001), SampEn (P = 0.031), RMSSD (P < 0.001), SDNN (P < 0.001), LF power (P < 0.001) and HF power (P < 0.001), HRV metrics with ageing. There was no significant effect of age the complexity metrics DFA α1 (P = 0.107), α2 (P = 0.147) and CI-8 (P = 0.493). CONCLUSION: HRV metrics are reproducible between days in both healthy highly active younger and older adults. There is a decline in linear and nonlinear HRV metrics with age, albeit there being no age-related change in the nonlinear metrics, DFA α1, α2 and CI-8.

What Does It Take to Complete the Cape Epic?

ABSTRACT: Reinpõld, K, Bossi, AH, and Hopker, JG. What does it take to complete the cape epic? J Strength Cond Res 36(12): 3513-3520, 2022-This study aimed to describe the racing and training demands of the Cape Epic. Six male mountain bike riders (age: 39 ± 7 years, height: 181 ± 3 cm, and body mass: 78.7 ± 8.1 kg) trained for 4.5 months and took part in the Cape Epic. Training and racing data (prologue, stage 1, and 2) were analyzed, and riders were tested in the laboratory on 3 distinct occasions for maximal oxygen uptake (V̇O 2 max), maximal work rate (Wmax), and power output associated with the respiratory compensation point (RCP PO ). Statistical significance was set at p ≤ 0.05. With race durations of 1.5 ± 0.2, 6.5 ± 1.2, and 6.4 ± 1.4 hours for, respectively, prologue, stage 1, and 2, normalized power was higher in prologue (3.73 ± 0.72 W·kg -1 ) compared with stages 1 (3.06 ± 0.59 W·kg -1 , p < 0.001) and 2 (2.94 ± 0.69 W·kg -1 , p < 0.001). Riders spent more time in power zones 1 and 2 (as %RCP PO ) and less time in zones 4 and 5, during stage 2 compared with prologue (all zones p ≤ 0.028). Despite no changes in V̇O 2 max or Wmax, RCP PO increased from midtraining (3.89 ± 0.61 W·kg -1 ) to prerace testing (4.08 ± 0.64 W·kg -1 , p = 0.048). No differences were found between base and build training phases for time in power zones. In conclusion, the Cape Epic requires an ability to sustain high submaximal power outputs for several hours as well as an ability to repeat high-intensity efforts throughout the race. A well-balanced program, incorporating a pyramidal intensity distribution, may be used as a starting point for the design of optimal training approaches.

The acute physiological and perceptual effects of recovery interval intensity during cycling-based high-intensity interval training.

PURPOSE: The current study sought to investigate the role of recovery intensity on the physiological and perceptual responses during cycling-based aerobic high-intensity interval training. METHODS: Fourteen well-trained cyclists ([Formula: see text]: 62 ± 9 mL kg-1 min-1) completed seven laboratory visits. At visit 1, the participants' peak oxygen consumption ([Formula: see text]) and lactate thresholds were determined. At visits 2-7, participants completed either a 6 × 4 min or 3 × 8 min high-intensity interval training (HIIT) protocol with one of three recovery intensity prescriptions: passive (PA) recovery, active recovery at 80% of lactate threshold (80A) or active recovery at 110% of lactate threshold (110A). RESULTS: The time spent at > 80%, > 90% and > 95% of maximal minute power during the work intervals was significantly increased with PA recovery, when compared to both 80A and 110A, during both HIIT protocols (all P ≤ 0.001). However, recovery intensity had no effect on the time spent at > 90% [Formula: see text] (P = 0.11) or > 95% [Formula: see text] (P = 0.50) during the work intervals of both HIIT protocols. Session RPE was significantly higher following the 110A recovery, when compared to the PA and 80A recovery during both HIIT protocols (P < 0.001). CONCLUSION: Passive recovery facilitates a higher work interval PO and similar internal stress for a lower sRPE when compared to active recovery and therefore may be the efficacious recovery intensity prescription.

The effect of mental fatigue on critical power during cycling exercise.

PURPOSE: Time to exhaustion (TTE) tests used in the determination of critical power (CP) and curvature constant (W') of the power-duration relationship are strongly influenced by the perception of effort (PE). This study aimed to investigate whether manipulation of the PE alters the CP and W'. METHODS: Eleven trained cyclists completed a series of TTE tests to establish CP and W' under two conditions, following a mentally fatiguing (MF), or a control (CON) task. Both cognitive tasks lasted 30 min followed by a TTE test. Ratings of PE and heart rate (HR) were measured during each TTE. Blood lactate was taken pre and post each TTE test. Ratings of perceived mental and physical fatigue were taken pre- and post-cognitive task, and following each TTE test. RESULTS: Perceived MF significantly increased as a result of the MF task compared to baseline and the CON task (P < 0.05), without a change in perceived physical fatigue (P > 0.05). PE was significantly higher during TTE in the MF condition (P < 0.05). Pre-post blood lactate accumulation was significantly lower after each TTE in MF condition (P < 0.05). HR was not significant different between conditions (P > 0.05). Neither cognitive task induced any change in CP (MF 253 ± 51 vs. CON 247 ± 58W; P > 0.05), although W' was significantly reduced in the MF condition (MF 22.8 ± 4.5 vs. CON 29.3 ± 6.3 kJ; P < 0.01). CONCLUSION: MF has no effect of CP, but reduces the W' in trained cyclists. Lower lactate accumulation during TTE tests following MF suggests that cyclists were not able to fully expend W' even though they exercised to volitional exhaustion.

Prescribing 6-weeks of running training using parameters from a self-paced maximal oxygen uptake protocol.

PURPOSE: The self-paced maximal oxygen uptake test (SPV) may offer effective training prescription metrics for athletes. This study aimed to examine whether SPV-derived data could be used for training prescription. METHODS: Twenty-four recreationally active male and female runners were randomly assigned between two training groups: (1) Standardised (STND) and (2) Self-Paced (S-P). Participants completed 4 running sessions a week using a global positioning system-enabled (GPS) watch: 2 × interval sessions; 1 × recovery run; and 1 × tempo run. STND had training prescribed via graded exercise test (GXT) data, whereas S-P had training prescribed via SPV data. In STND, intervals were prescribed as 6 × 60% of the time that velocity at [Formula: see text] ([Formula: see text]) could be maintained (Tmax). In S-P, intervals were prescribed as 7 × 120 s at the mean velocity of rating of perceived exertion 20 (vRPE20). Both groups used 1:2 work:recovery ratio. Maximal oxygen uptake ([Formula: see text]), [Formula: see text], Tmax, vRPE20, critical speed (CS), and lactate threshold (LT) were determined before and after the 6-week training. RESULTS: STND and S-P training significantly improved [Formula: see text] by 4 ± 8 and 6 ± 6%, CS by 7 ± 7 and 3 ± 3%; LT by 5 ± 4% and 7 ± 8%, respectively (all P < .05), with no differences observed between groups. CONCLUSIONS: Novel metrics obtained from the SPV can offer similar training prescription and improvement in [Formula: see text], CS and LT compared to training derived from a traditional GXT.

The effects of acute carbohydrate and caffeine feeding strategies on cycling efficiency.

To assess the effect of carbohydrate and caffeine on gross efficiency (GE), 14 cyclists (V̇O2max 57.6 ± 6.3 ml.kg-1.min-1) completed 4 × 2-hour tests at a submaximal exercise intensity (60% Maximal Minute Power). Using a randomized, counter-balanced crossover design, participants consumed a standardised diet in the 3-days preceding each test and subsequently ingested either caffeine (CAF), carbohydrate (CHO), caffeine+carbohydrate (CAF+CHO) or water (W) during exercise whilst GE and plasma glucose were assessed at regular intervals (~30 mins). GE progressively decreased in the W condition but, whilst caffeine had no effect, this was significantly attenuated in both trials that involved carbohydrate feedings (W = -1.78 ± 0.31%; CHO = -0.70 ± 0.25%, p = 0.008; CAF+CHO = -0.63 ± 0.27%, p = 0.023; CAF = -1.12 ± 0.24%, p = 0.077). Blood glucose levels were significantly higher in carbohydrate ingestion conditions (CHO = 4.79 ± 0.67 mmol·L-1, p < 0.001; CAF+CHO = 5.05 ± 0.81 mmol·L-1, p < 0.001; CAF = 4.46 ± 0.75 mmol·L-1; W = 4.20 ± 0.53 mmol·L-1). Carbohydrate ingestion has a small but significant effect on exercise-induced reductions in GE, indicating that cyclists' feeding strategy should be carefully monitored prior to and during assessment.

Age differences in physiological responses to self-paced and incremental [Formula: see text] testing.

PURPOSE: A self-paced maximal exercise protocol has demonstrated higher [Formula: see text] values when compared against traditional tests. The aim was to compare physiological responses to this self-paced [Formula: see text] protocol (SPV) in comparison to a traditional ramp [Formula: see text] (RAMP) protocol in young (18-30 years) and old (50-75 years) participants. METHODS: Forty-four participants (22 young; 22 old) completed both protocols in a randomised, counter-balanced, crossover design. The SPV included 5 × 2 min stages, participants were able to self-regulate their power output (PO) by using incremental 'clamps' in ratings of perceived exertion. The RAMP consisted of either 15 or 20 W min-1. RESULTS: Expired gases, cardiac output (Q), stroke volume (SV), muscular deoxyhaemoglobin (deoxyHb) and electromyography (EMG) at the vastus lateralis were recorded throughout. Results demonstrated significantly higher [Formula: see text] in the SPV (49.68 ± 10.26 ml kg-1 min-1) vs. the RAMP (47.70 ± 9.98 ml kg-1 min-1) in the young, but not in the old group (>0.05). Q and SV were significantly higher in the SPV vs. the RAMP in the young (<0.05) but not in the old group (>0.05). No differences seen in deoxyHb and EMG for either age groups (>0.05). Peak PO was significantly higher in the SPV vs. the RAMP in both age groups (<0.05). CONCLUSION: Findings demonstrate that the SPV produces higher [Formula: see text], peak Q and SV values in the young group. However, older participants achieved similar [Formula: see text] values in both protocols, mostly likely due to age-related differences in cardiovascular responses to incremental exercise, despite them achieving a higher physiological workload in the SPV.

Central alterations of neuromuscular function and feedback from group III-IV muscle afferents following exhaustive high-intensity one-leg dynamic exercise.

The aims of this investigation were to describe the central alterations of neuromuscular function induced by exhaustive high-intensity one-leg dynamic exercise (OLDE, study 1) and to indirectly quantify feedback from group III-IV muscle afferents via muscle occlusion (MO, study 2) in healthy adult male humans. We hypothesized that these central alterations and their recovery are associated with changes in afferent feedback. Both studies consisted of two time-to-exhaustion tests at 85% peak power output. In study 1, voluntary activation level (VAL), M-wave, cervicomedullary motor evoked potential (CMEP), motor evoked potential (MEP), and MEP cortical silent period (CSP) of the knee extensor muscles were measured. In study 2, mean arterial pressure (MAP) and leg muscle pain were measured during MO. Measurements were performed preexercise, at exhaustion, and after 3 min recovery. Compared with preexercise values, VAL was lower at exhaustion (-13 ± 13%, P < 0.05) and after 3 min of recovery (-6 ± 6%, P = 0.05). CMEP area/M area was lower at exhaustion (-38 ± 13%, P < 0.01) and recovered after 3 min. MEP area/M area was higher at exhaustion (+25 ± 27%, P < 0.01) and after 3 min of recovery (+17 ± 20%, P < 0.01). CSP was higher (+19 ± 9%, P < 0.01) only at exhaustion and recovered after 3 min. Markers of afferent feedback (MAP and leg muscle pain during MO) were significantly higher only at exhaustion. These findings suggest that the alterations in spinal excitability and CSP induced by high-intensity OLDE are associated with an increase in afferent feedback at exhaustion, whereas central fatigue does not fully recover even when significant afferent feedback is no longer present.

The effect of transcranial direct current stimulation of the motor cortex on exercise-induced pain.

PURPOSE: Transcranial direct current stimulation (tDCS) provides a new exciting means to investigate the role of the brain during exercise. However, this technique is not widely used in exercise science, with little known regarding effective electrode montages. This study investigated whether tDCS of the motor cortex (M1) would elicit an analgesic response to exercise-induced pain (EIP). METHODS: Nine participants completed a VO2max test and three time to exhaustion (TTE) tasks on separate days following either 10 min 2 mA tDCS of the M1, a sham or a control. Additionally, seven participants completed 3 cold pressor tests (CPT) following the same experimental conditions (tDCS, SHAM, CON). Using a well-established tDCS protocol, tDCS was delivered by placing the anodal electrode above the left M1 with the cathodal electrode above dorsolateral right prefrontal cortex. Gas exchange, blood lactate, EIP and ratings of perceived exertion (RPE) were monitored during the TTE test. Perceived pain was recorded during the CPT. RESULTS: During the TTE, no significant differences in time to exhaustion, RPE or EIP were found between conditions. However, during the CPT, perceived pain was significantly (P < 0.05) reduced in the tDCS condition (7.4 ± 1.2) compared with both the CON (8.6 ± 1.0) and SHAM (8.4 ± 1.3) conditions. CONCLUSION: These findings demonstrate that stimulation of the M1 using tDCS does not induce analgesia during exercise, suggesting that the processing of pain produced via classic measures of experimental pain (i.e., a CPT) is different to that of EIP. These results provide important methodological advancement in developing the use of tDCS in exercise.

The effect of acetaminophen ingestion on cortico-spinal excitability.

Acetaminophen (ACT) facilitates the inhibition of voltage-gated calcium and sodium currents, which may effect cortico-spinal excitability. Twelve subjects ingested acetaminophen or a placebo and underwent transcranial magnetic stimulation to assess the motor evoked potential (MEP), and cortical silent period (CSP). ACT significantly increased MEP response (P > 0.05) but had no effect on CSP (P > 0.05). This indicates that ACT increases MEP and should be controlled for in studies where these measures are of interest.

Reproducibility of NIRS-derived mitochondrial oxidative capacity in highly active older adults.

INTRODUCTION: In-vivo techniques using near-infrared spectroscopy (NIRS) have been developed to assess skeletal muscle mitochondrial oxidative capacity. However, the test-retest and day-to-day reliability of NIRS-derived mitochondrial oxidative capacity has yet to be established in older individuals. Therefore, the primary aim of this study was to determine the day-to-day and test-retest reliability of NIRS-derived mitochondrial oxidative capacity in older adults. The secondary aim was to examine the relationship between NIRS-derived mitochondrial capacity and whole-body aerobic fitness. MATERIAL AND METHODS: Twenty-four healthy individuals (19 M, 5F; aged 60 ± 4 years; maximal oxygen uptake (V̇O2peak) = 41.2 ± 6.8 ml.kg-1.min-1) completed three visits to the laboratory. Visit one assessed isometric maximal voluntary contractions of the knee extensors and aerobic capacity through an incremental exercise test. In visits two and three participants completed two measurements of NIRS-derived mitochondrial oxidative capacity in the vastus lateralis (VL). RESULTS: NIRS-derived mitochondrial oxidative capacity was found to have good to excellent day-to-day reliability (Day 1 vs Day 2; coefficient of variation (CV) = 7.0 %; standard error of measurement (SEM) = 5.2; intra-class correlation coefficient (ICC) = 0.94) and test re-test reliability (Day 1 [Test 1 vs Test 2]; CV = 5.0 %; SEM = 3.7; ICC 0.97 and Day 2 [Test 1 vs Test 2]; CV = 6.3 %; SEM = 4.9; ICC = 0.93). NIRS-derived mitochondrial oxidative capacity was found to be significantly correlated with V̇O2peak (r = -0.61; R2 = 0.37; P = 0.002), oxygen uptake at the gas exchange threshold (r = -0.49; R2 = 0.24; P = 0.02), and oxygen uptake at the respiratory compensation point (r = -0.57; R2 = 0.32; P = 0.004). CONCLUSION: NIRS provides a reliable method for deriving a measure of VL mitochondrial oxidative capacity in highly active older adults and demonstrates a significant relationship with measures of whole-body aerobic fitness.

Competitive performance as a discriminator of doping status in elite athletes.

As the aim of any doping regime is to improve sporting performance, it has been suggested that analysis of athlete competitive results might be informative in identifying those at greater risk of doping. This research study aimed to investigate the utility of a statistical performance model to discriminate between athletes who have a previous anti-doping rule violation (ADRV) and those who do not. We analysed performances of male and female 100 and 800 m runners obtained from the World Athletics database using a Bayesian spline model. Measures of unusual improvement in performance were quantified by comparing the yearly change in athlete's performance (delta excess performance) to quantiles of performance in their age-matched peers from the database population. The discriminative ability of these measures was investigated using the area under the ROC curve (AUC) with the 55%, 75% and 90% quantiles of the population performance. The highest AUC values across age were identified for the model with a 75% quantile (AUC = 0.78-0.80). The results of this study demonstrate that delta excess performance was able to discriminate between athletes with and without ADRVs and therefore could be used to assist in the risk stratification of athletes for anti-doping purposes.

Variability in Submaximal Self-Paced Exercise Bouts of Different Intensity and Duration.

PURPOSE: Rating of perceived exertion (RPE) as a training-intensity prescription has been extensively used by athletes and coaches. However, individual variability in the physiological response to exercise prescribed using RPE has not been investigated. METHODS: Twenty well-trained competitive cyclists (male = 18, female = 2, maximum oxygen consumption = 55.07 [11.06] mL·kg-1·min-1) completed 3 exercise trials each consisting of 9 randomized self-paced exercise bouts of either 1, 4, or 8 minutes at RPEs of 9, 13, and 17. Within-athlete variability (WAV) and between-athletes variability (BAV) in power and physiological responses were calculated using the coefficient of variation. Total variability was calculated as the ratio of WAV to BAV. RESULTS: Increased RPEs were associated with higher power, heart rate, work, volume of expired oxygen (VO2), volume of expired carbon dioxide (VCO2), minute ventilation (VE), deoxyhemoglobin (ΔHHb) (P < .001), and lower tissue saturation index (ΔTSI%) and ΔO2Hb (oxyhaemoglobin; P < .001). At an RPE of 9, shorter durations resulted in lower VO2 (P < .05) and decreased ΔTSI%, and the ΔHHb increased as the duration increased (P < .05). At an RPE of 13, shorter durations resulted in lower VO2, VE, and percentage of maximum oxygen consumption (P < .001), as well as higher power, heart rate, ΔHHb (P < .001), and ΔTSI% (P < .05). At an RPE of 17, power (P < .001) and ΔTSI% (P < .05) increased as duration decreased. As intensity and duration increased, WAV and BAV in power, work, heart rate, VO2, VCO2, and VE decreased, and WAV and BAV in near-infrared spectroscopy increased. CONCLUSIONS: Self-paced intensity prescriptions of high effort and long duration result in the greatest consistency on both a within- and between-athletes basis.

The Acute Physiological and Perceptual Effects of Individualizing the Recovery Interval Duration Based Upon the Resolution of Muscle Oxygen Consumption During Cycling Exercise.

PURPOSE: There has been paucity in research investigating the individualization of recovery interval duration during cycling-based high-intensity interval training (HIIT). The main aim of the study was to investigate whether individualizing the duration of the recovery interval based upon the resolution of muscle oxygen consumption would improve the performance during work intervals and the acute physiological response of the HIIT session, when compared with a standardized (2:1 work recovery ratio) approach. METHODS: A total of 16 well-trained cyclists (maximal oxygen consumption: 60 [7] mL·kg-1·min-1) completed 6 laboratory visits: (Visit 1) incremental exercise test, (Visit 2) determination of the individualized (IND) recovery duration, using the individuals' muscle oxygen consumption recovery duration to baseline from a 4- and 8-minute work interval, (Visits 3-6) participants completed a 6 × 4- and a 3 × 8-minute HIIT session twice, using the IND and standardized recovery intervals. RESULTS: Recovery duration had no effect on the percentage of the work intervals spent at >90% and >95% of maximal oxygen consumption, maximal minute power output, and maximal heart rate, during the 6 × 4- and 3 × 8-minute HIIT sessions. Recovery duration had no effect on mean work interval power output, heart rate, oxygen consumption, blood lactate, and rating of perceived exertion. There were no differences in reported session RPE between recovery durations for the 6 × 4- and 3 × 8-minute HIIT sessions. CONCLUSION: Individualizing HIIT recovery duration based upon the resolution of muscle oxygen consumption to baseline levels does not improve the performance of the work intervals or the acute physiological response of the HIIT session, when compared with standardized recovery duration.

The Self-Paced Submaximal Run Test: Associations With the Graded Exercise Test and Reliability.

PURPOSE: To assess the reliability and construct validity of a self-paced, submaximal run test (SRTRPE) for monitoring aerobic fitness. The SRTRPE monitors running velocity (v), heart rate (HRex), and blood lactate concentration (B[La]), during three 3-minute stages prescribed by ratings of perceived exertion (RPEs) of 10, 13, and 17. METHODS: Forty (14 female) trained endurance runners completed a treadmill graded exercise test for the determination of maximal oxygen consumption (VO2max), v at VO2max (vVO2max), and v at 2 mmol·L-1 (vLT1) and 4 mmol·L-1 (vLT2) B[La]. Within 7 days, participants completed the SRTRPE. Convergent validity between the SRTRPE and graded exercise test parameters was assessed through linear regression. Eleven participants completed a further 2 trials of the SRTRPE within a 72-hour period to quantify test-retest reliability. RESULTS: There were large correlations between v at all stages of the SRTRPE and VO2max (r range = .57-.63), vVO2max (.50-.66), and vLT2 (.51-.62), with vRPE 17 displaying the strongest associations (r > .60). Intraclass correlation coefficients (ICC3,1) were moderate to high for parameters v (range = .76-.84), HRex (.72-.92), and %HRmax (.64-.89) at all stages of the SRTRPE. The corresponding coefficients of variation were 2.5% to 5.6%. All parameters monitored at intensity RPE 17 displayed the greatest reliability. CONCLUSIONS: The SRTRPE was shown to be a valid and reliable test for monitoring parameters associated with aerobic fitness, displaying the potential of this submaximal, time-efficient test to monitor responses to endurance training.

Energy Expenditure Equation Choice: Effects on Cycling Efficiency and its Reliability.

PURPOSE: There are several published equations to calculate energy expenditure (EE) from gas exchanges. The authors assessed whether using different EE equations would affect gross efficiency (GE) estimates and their reliability. METHODS: Eleven male and 3 female cyclists (age 33 [10] y; height: 178 [11] cm; body mass: 76.0 [15.1] kg; maximal oxygen uptake: 51.4 [5.1] mL·kg-1·min-1; peak power output: 4.69 [0.45] W·kg-1) completed 5 visits to the laboratory on separate occasions. In the first visit, participants completed a maximal ramp test to characterize their physiological profile. In visits 2 to 5, participants performed 4 identical submaximal exercise trials to assess GE and its reliability. Each trial included three 7-minute bouts at 60%, 70%, and 80% of the gas exchange threshold. EE was calculated with 4 equations by Péronnet and Massicotte, Lusk, Brouwer, and Garby and Astrup. RESULTS: All 4 EE equations produced GE estimates that differed from each other (all P < .001). Reliability parameters were only affected when the typical error was expressed in absolute GE units, suggesting a negligible effect-related to the magnitude of GE produced by each EE equation. The mean coefficient of variation for GE across different exercise intensities and calculation methods was 4.2%. CONCLUSIONS: Although changing the EE equation does not affect GE reliability, exercise scientists and coaches should be aware that different EE equations produce different GE estimates. Researchers are advised to share their raw data to allow for GE recalculation, enabling comparison between previous and future studies.

Optimizing Interval Training Through Power-Output Variation Within the Work Intervals.

PURPOSE: Maximal oxygen uptake (V˙O2max) is a key determinant of endurance performance. Therefore, devising high-intensity interval training (HIIT) that maximizes stress of the oxygen-transport and -utilization systems may be important to stimulate further adaptation in athletes. The authors compared physiological and perceptual responses elicited by work intervals matched for duration and mean power output but differing in power-output distribution. METHODS: Fourteen cyclists (V˙O2max 69.2 [6.6] mL·kg-1·min-1) completed 3 laboratory visits for a performance assessment and 2 HIIT sessions using either varied-intensity or constant-intensity work intervals. RESULTS: Cyclists spent more time at >90%V˙O2max during HIIT with varied-intensity work intervals (410 [207] vs 286 [162] s, P = .02), but there were no differences between sessions in heart-rate- or perceptual-based training-load metrics (all P ≥ .1). When considering individual work intervals, minute ventilation (V˙E) was higher in the varied-intensity mode (F = 8.42, P = .01), but not respiratory frequency, tidal volume, blood lactate concentration [La], ratings of perceived exertion, or cadence (all F ≤ 3.50, ≥ .08). Absolute changes (Δ) between HIIT sessions were calculated per work interval, and Δ total oxygen uptake was moderately associated with ΔV˙E (r = .36, P = .002). CONCLUSIONS: In comparison with an HIIT session with constant-intensity work intervals, well-trained cyclists sustain higher fractions of V˙O2max when work intervals involved power-output variations. This effect is partially mediated by an increased oxygen cost of hyperpnea and not associated with a higher [La], perceived exertion, or training-load metrics.