Oxygen uptake plateau occurrence depends on oxygen kinetics and oxygen deficit accumulation

We tested the hypothesis that participants with an oxygen uptake () plateau during incremental exercise exhibit a lower VO₂‐deficit (VO_2DEF)‐accumulation in the submaximal intensity domain due to faster ramp and square wave O₂‐kinetics. Twenty‐six male participants performed a standard ramp test (increment: 30 W·min^?1), a ramp test with an individualized ramp slope and a two‐step (moderate and severe) square wave exercise followed by a ‐verification bout. VO_2DEF was calculated by the difference between individualized ramp test O₂ and O₂‐demand estimated from steady‐state O₂‐kinetics. Twenty‐four participants verified their O_2max in the verification test. Ten of them showed a plateau in the individualized ramp test. VO_2DEF at the end of this ramp test (4.34 ± 0.60 vs 4.54 ± 0.43 L) was not different between the plateau and the non‐plateau group (P > 0.05). The plateau group had a significantly (P < 0.05) lower VO_2DEF 2 minutes before termination of the individualized ramp test (2.24 ± 0.40 vs 2.78 ± 0.33 L). This coincided with a shorter mean response time (43 ± 9 vs 53 ± 7 seconds), a higher increase in O₂ per W (10.1 ± 0.2 vs 9.2 ± 0.5 mL·min^?1·W^?1) at the individualized ramp test as well as shorter time constants of moderate (36 ± 6 vs 48 ± 7 seconds) and severe (62 ± 9 vs 86 ± 10 seconds) square wave kinetics (all P < 0.05). We conclude that the O₂‐plateau occurrence requires a fast O₂‐kinetics and a low VO_2DEF‐accumulation at intensities below O_2max.     

Effect of beta2‐adrenergic agonist and resistance training on maximal oxygen uptake and muscle oxidative enzymes in men

While beta₂‐adrenoceptor stimulation has been shown to increase lean mass and to alter metabolic properties of skeletal muscle, adaptations in muscle oxidative enzymes and maximal oxygen uptake (O_2max) in response to beta₂‐adrenergic agonist treatment are inadequately explored in humans, particularly in association with resistance training. Herein, we investigated beta₂‐adrenergic‐induced changes in O_2max, leg and arm composition, and muscle content of oxidative enzymes in response to treatment with the selective beta₂‐adrenergic agonist terbutaline with and without concurrent resistance training in young men. Forty‐six subjects were randomized to 4 weeks of lifestyle maintenance (n = 23) or resistance training (n = 23). Within the lifestyle maintenance and resistance training group, subjects received daily terbutaline (8 × 0.5 mg) (n = 13) or placebo (n = 10) treatment. No apparent treatment by training interactions was observed during the study period. Terbutaline increased leg and arm lean mass with the intervention, whereas no treatment differences were observed in absolute O_2max and incremental peak power output (iPPO). Treatment main effects were observed for O₂‐reserve (P < .05), O_2max relative to body mass (P < .05), O_2max relative to leg lean mass (P < .01), and iPPO relative to leg lean mass, in which terbutaline had a negative effect compared with placebo. Furthermore, content of electron transport chain complex I‐V decreased by 11% (P < .05) for terbutaline compared with placebo. Accordingly, chronic treatment with the selective beta₂‐adrenergic agonist terbutaline may negatively affect O_2max and iPPO in relative terms, but not in absolute.     

Merging self-reported with technically sensed data for tracking mobility behavior in a naturalistic intervention study. Insights from the GISMO study

Sound exposure data are central for any intervention study. In the case of utilitarian mobility, where studies cannot be conducted in controlled environments, exposure data are commonly self-reported. For short-term intervention studies, wearable devices with location sensors are increasingly employed. We aimed to combine self-reported and technically sensed mobility data, in order to provide more accurate and reliable exposure data for GISMO, a long-term intervention study. Through spatio-temporal data matching procedures, we are able to determine the amount of mobility for all modes at the best possible accuracy level. Self-reported data deviate ±10% from the corrected reference. Derived modal split statistics prove high compliance to the respective recommendations for the control group (CG) and the two intervention groups (IG-PT, IG-C). About 73.7% of total mileage was travelled by car in CG. This share was 10.3% (IG-PT) and 9.7% (IG-C), respectively, in the intervention groups. Commuting distances were comparable in CG and IG, but annual mean travel times differ between  = 8,458 min (σ = 6,427 min) for IG-PT,  = 8,444 min (σ = 5,961 min) for IG-C, and  = 5,223 min (σ = 5,463 min) for CG. Seasonal variabilities of modal split statistics were observable. However, in IG-PT and IG-C no shift toward the car occurred during winter months. Although no perfect single-method solution for acquiring exposure data in mobility-related, naturalistic intervention studies exists, we achieved substantially improved results by combining two data sources, based on spatio-temporal matching procedures.     

Increased oxygen extraction and mitochondrial protein expression after small muscle mass endurance training

When exercising with a small muscle mass, the mass-specific O₂ delivery exceeds the muscle oxidative capacity resulting in a lower O₂ extraction compared with whole-body exercise. We elevated the muscle oxidative capacity and tested its impact on O₂ extraction during small muscle mass exercise. Nine individuals conducted six weeks of one-legged knee extension (1L-KE) endurance training. After training, the trained leg (TL) displayed 45% higher citrate synthase and COX-IV protein content in vastus lateralis and 15%-22% higher pulmonary oxygen uptake ( ) and peak power output ( ) during 1L-KE than the control leg (CON; all P < .05). Leg O₂ extraction (catheters) and blood flow (ultrasound Doppler) were measured while both legs exercised simultaneously during 2L-KE at the same submaximal power outputs (real-time feedback-controlled). TL displayed higher O₂ extraction than CON (main effect: 1.7 ± 1.6% points; P = .010; 40%-83% of ) with the largest between-leg difference at 83% of (O₂ extraction: 3.2 ± 2.2% points; arteriovenous O₂ difference: 7.1 ± 4.8 mL· L⁻¹; P < .001). At 83% of , muscle O₂ conductance (D_MO₂; Fick law of diffusion) and the equilibration index Y were higher in TL (P < .01), indicating reduced diffusion limitations. The between-leg difference in O₂ extraction correlated with the between-leg ratio of citrate synthase and COX-IV (r = .72-.73; P = .03), but not with the difference in the capillary-to-fiber ratio (P = .965). In conclusion, endurance training improves O₂ extraction during small muscle mass exercise by elevating the muscle oxidative capacity and the recruitment of D_MO_2, especially evident during high-intensity exercise exploiting a larger fraction of the muscle oxidative capacity.     

Superior performance improvements in elite cyclists following short-interval vs effort-matched long-interval training

The purpose of this study was to compare the effects of 3 weeks with three weekly sessions (ie, nine sessions in total) of short intervals (SI; n = 9; 3 series with 13 × 30-second work intervals interspersed with 15-second recovery and 3-minutes recovery between series) against effort-matched (rate of perceived effort based) long intervals (LI; n = 9; 4 series of 5-minute work intervals with 2.5-minutes recovery between series) on performance parameters in elite cyclists ( 73 ± 4 mL min⁻¹ kg⁻¹). There were no differences between groups in total volume and intensity distribution of training during the intervention period. SI achieved a larger (P < .05) relative improvement in peak aerobic power output than LI (3.7 ± 4.3% vs −0.3 ± 2.8%, respectively), fractional utilization of at 4 mmol L⁻¹ [La⁻] (3.0 ± 5.8 percent points vs −3.5 ± 2.7 percent points, respectively), and larger relative increase in power output at 4 mmol L⁻¹ [La⁻] (2.0 ± 6.7% vs −2.8 ± 3.4, respectively), while there was no group difference in change of . Improvements in performance measured as mean power output during 20-minute cycling test were greater (P < .01) in SI compared with LI (4.7 ± 4.4% vs −1.4 ± 2.2%, respectively). Mean effect size of the improvement in the above variables revealed a small to large effect of SI training vs LI training. The data thus demonstrate that the present SI protocol induces superior training adaptations compared with the present LI protocol in elite cyclists.     

Which exercise prescriptions optimize V̇O2max during cancer treatment?—A systematic review and meta‐analysis

The aims of the present systematic review and meta‐analysis were to investigate the effect of exercise on maximal oxygen uptake () and to investigate whether exercise frequency, intensity, duration, and volume are associated with changes in among adult patients with cancer undergoing treatment. Medline and Embase through OvidSP were searched to identify randomized controlled trials. Two reviewers extracted data and assessed the risk of bias. The overall effect size and differences in effects for different intensities and frequencies were calculated on change scores and post‐intervention data, and the meta‐regression of exercise duration and volumes was analyzed using the Comprehensive Meta‐Analysis software. Fourteen randomized controlled trials were included in the systematic review, comprising 1332 patients with various cancer types receiving (neo‐)adjuvant chemo‐, radio‐, and/or hormone therapy. Exercise induced beneficial changes in compared to usual care (effect size = 0.46, 95% Confidence Interval = 0.23‐0.69). Longer session duration (P = 0.020), and weekly duration (P = 0.010), larger weekly volume (P < 0.001), and shorter intervention duration (P = 0.005) were significantly associated with more beneficial changes in . No differences in effects between subgroups with respect to frequency and intensity were found. In conclusion, exercise has beneficial effects on in patients with cancer undergoing (neo‐)adjuvant treatment. As interventions with larger exercise volumes and longer session durations resulted in larger beneficial changes in , exercise frequency, intensity, and duration should be considered carefully for sufficient exercise volume to induce changes in for this patient group.     

Exercise training‐induced visceral fat loss in obese women: The role of training intensity and modality

Visceral fat loss in response to four‐cycle ergometer training regimens with explicit differences in exercise intensity and modality was compared. Fifty‐nine obese young women (body fat percentage ≥ 30%) were randomized to a 12‐week intervention consisting of either all‐out sprint interval training (SIT_all‐out, n = 11); supramaximal SIT (SIT₁₂₀, 120% O_2peak, n = 12); high‐intensity interval training (HIIT₉₀, 90% O_2peak, n = 12), moderate‐intensity continuous training (MICT, 60% O_2peak, n = 11), or no training (CON, n = 13). The total work done per training session in SIT₁₂₀, HIIT₉₀, and MICT was confined to 200 kJ, while it was deliberately lower in SIT_all‐out. The abdominal visceral fat area (AVFA) was measured through computed tomography scans. The whole‐body and regional fat mass were assessed through dual‐energy X‐ray absorptiometry. Pre‐, post‐, and 3‐hour post‐exercise serum growth hormone (GH), and epinephrine (EPI) were measured during selected training sessions. Following the intervention, similar reductions in whole‐body and regional fat mass were found in all intervention groups, while the reductions in AVFA resulting from SIT_all‐out, SIT₁₂₀, and HIIT₉₀ (>15 cm²) were greater in comparison with MICT (<3.5 cm², P < .05). The AVFA reductions among the SITs and HIIT groups were similar, and it was concomitant with the similar exercise‐induced releases of serum GH and EPI. CON variables were unchanged. These findings suggest that visceral fat loss induced by interval training at or above 90% O_2peak appeared unresponsive to the change in training intensity. Nonetheless, SIT_all‐out is still the most time‐efficient strategy among the four exercise‐training regimes for controlling visceral obesity.     

The relationship between peak fat oxidation and prolonged double-poling endurance exercise performance

The peak fat oxidation rate (PFO) and the exercise intensity that elicits PFO (Fat_max) are associated with endurance performance during exercise primarily involving lower body musculature, but it remains elusive whether these associations are present during predominant upper body exercise. The aim was to investigate the relationship between PFO and Fat_max determined during a graded exercise test on a ski-ergometer using double-poling (GET-DP) and performance in the long-distance cross-country skiing race, Vasaloppet. Forty-three healthy men completed GET-DP and Vasaloppet and were divided into two subgroups: recreational (RS, n = 35) and elite (ES, n = 8) skiers. Additionally, RS completed a cycle-ergometer GET (GET-Cycling) to elucidate whether the potential relationships were specific to exercise modality. PFO (r² = .10, P = .044) and Fat_max (r² = .26, P < .001) were correlated with performance; however, was the only independent predictor of performance (adj. R² = .36) across all participants. In ES, Fat_max was the only variable associated with performance (r² = .54, P = .038). Within RS, DP (r² = .11, P = .047) and ski-specific training background (r² = .30, P = .001) were associated with performance. Between the two GETs, Fat_max (r² = .20, P = .006) but not PFO (r² = .07, P = .135) was correlated. Independent of exercise mode, neither PFO nor Fat_max were associated with performance in RS (P > .05). These findings suggest that prolonged endurance performance is related to PFO and Fat_max but foremost to during predominant upper body exercise. Interestingly, Fat_max may be an important determinant of performance among ES. Among RS, DP , and skiing experience appeared as performance predictors. Additionally, whole-body fat oxidation seemed specifically coupled to exercise modality.     

Predefined vs data-guided training prescription based on autonomic nervous system variation: A systematic review

Monitoring variations in the functioning of the autonomic nervous system may help personalize training of runners and provide more pronounced physiological adaptations and performance improvements. We systematically reviewed the scientific literature comparing physiological adaptations and/or improvements in performance following training based on responses of the autonomic nervous system (ie, changes in heart rate variability) and predefined training. PubMed, SPORTDiscus, and Web of Science were searched systematically in July 2019. Keywords related to endurance, running, autonomic nervous system, and training. Studies were included if they (a) involved interventions consisting predominantly of running training; (b) lasted at least 3 weeks; (c) reported pre- and post-intervention assessment of running performance and/or physiological parameters; (d) included an experimental group performing training adjusted continuously on the basis of alterations in HRV and a control group; and (e) involved healthy runners. Five studies involving six interventions and 166 participants fulfilled our inclusion criteria. Four HRV-based interventions reduced the amount of moderate- and/or high-intensity training significantly. In five interventions, improvements in performance parameters (3000 m, 5000 m, Loadmax, Tlim) were more pronounced following HRV-based training. Peak oxygen uptake () and submaximal running parameters (eg, LT1, LT2) improved following both HRV-based and predefined training, with no clear difference in the extent of improvement in . Submaximal running parameters tended to improve more following HRV-based training. Research findings to date have been limited and inconsistent. Both HRV-based and predefined training improve running performance and certain submaximal physiological adaptations, with effects of the former training tending to be greater.     

Effects of nitrate supplementation in trained and untrained muscle are modest with initial high plasma nitrite levels

Nitrate () supplementation resulting in higher plasma nitrite () is reported to lower resting mean arterial blood pressure (MAP) and oxygen uptake (VO₂) during submaximal exercise in non‐athletic populations, whereas effects in general are absent in endurance‐trained individuals. To test whether physiologic effects of supplementation depend on local muscular training status or cardiovascular fitness, male endurance‐trained cyclists (CYC, n=9, VO₂‐max: 64±3 mL/min/kg; mean±SD) and recreational active subjects serving as a control group (CON, n=8, 46±3 mL/min/kg), acutely consumed nitrate‐rich beetroot juice ([] ~9 mmol) (NIT) or placebo (PLA) with assessment of resting MAP and energy expenditure during moderate intensity (~50% VO₂‐max) and incremental leg cycling (LEG‐ex) and arm‐cranking exercise (ARM‐ex). NIT increased (P<.001) resting plasma by ~1200% relative to PLA. Plasma increased ~25% (P<.01) with a significant change only in CYC. LEG‐ex VO₂ (~2.60 L/min), ARM‐ex VO₂ (~1.14 L/min), and resting MAP (~87 mm Hg) remained unchanged for CYC, and similarly for CON, no changes were observed for LEG‐ex VO₂ (~2.03 L/min), ARM‐ex VO₂ (~1.06 L/min), or resting MAP (~85 mm Hg). VO₂‐max was not affected by supplementation, but incremental test peak power was higher (P<.05) in LEG‐ex for CYC in NIT relative to PLA (418±47 vs 407±46 W). In both CYC and CON, high initial baseline values and small increases in plasma after NIT may have lowered the effect of the intervention implying that muscular and cardiovascular training status is likely not the only factors that influence the physiologic effects of supplementation.     

Physical capacity,not skeletal maturity,distinguishes competitive levels in male Norwegian U14 soccer players

The main aim of the present study was to compare skeletal maturity level and physical capacities between male Norwegian soccer players playing at elite, sub-elite and non-elite level. Secondary, we aimed to investigate the association between skeletal maturity level and physical capacities. One hundred and two U14 soccer players (12.8-14.5 years old) recruited from four local clubs, and a regional team were tested for bone age and physical capacities. Bone age was estimated with x-ray of their left hand and used to indicate maturation of the skeleton. Players went through a comprehensive test battery to assess their physical capacities. Between-groups analysis revealed no difference in chronological age, skeletal maturity level, leg strength, body weight, or stature. However, elite players were superior to sub-elite and non-elite players on important functional characteristics as intermittent-endurance capacity (running distance: 1664 m ± 367 vs 1197 m ± 338 vs 693 m ± 235) and running speed (fastest 10 m split time: 1.27 seconds ± 0.06 vs 1.33 seconds ± 0.10 vs 1.39 seconds ± 0.11), in addition to maximal oxygen uptake (), standing long jump, and upper body strength (P < .05 for all comparisons). Medium-to-large correlations were found between skeletal maturity level and peak force (r = 695, P < .01), power (r = 684, P < .01), sprint (r = −.471, P<.001), and jump performance (r = .359, P < .01), but no correlation with upper body strength, , or intermittent-endurance capacity. These findings imply that skeletal maturity level does not bias the selection of players, although well-developed physical capacity clearly distinguishes competitive levels. The superior physical performance of the highest-ranked players seems related to an appropriate training environment.     

Effects of short‐term training and detraining on VO2 kinetics: Faster VO2 kinetics response after one training session

This study examined the time course of short‐term training and detraining‐induced changes in oxygen uptake () kinetics. Twelve men (24 ± 3 years) were assigned to either a 50% or a 70% of training intensity (n = 6 per group). was measured breath‐by‐breath. Changes in deoxygenated‐hemoglobin concentration (Δ[HHb]) were measured by near‐infrared spectroscopy. Moderate‐intensity exercise on‐transient and Δ[HHb] were modeled with a mono‐exponential and normalized (0–100% of response) and the ratio was calculated. Similar changes in time constant of () were observed in both groups. The combined group mean for decreased ～14% (32.3 to 27.9 s, P < 0.05) after one training session with a further ～11% decrease (27.9 to 24.8 s, P < 0.05) following two training sessions. The remained unchanged throughout the remaining of training and detraining. A significant “overshoot” in the ratio was decreased (albeit not significant) after one training session, and abolished (P < 0.05) after the second one, with no overshoot observed thereafter. Speeding of kinetics was remarkably quick with no further changes being observed with continuous training or during detraining. Improve matching of local O₂ delivery to O₂ utilization is a mechanism proposed to influence this response.     

Relationship between changes in pulmonary kinetics and autonomic regulation of blood flow

Various regulatory mechanisms of pulmonary oxygen uptake () kinetics have been postulated. The purpose of this study was to investigate the relationship between vagal withdrawal, measured using RMSSDRR, the root mean square of successive differences in cardiac interval (RR) kinetics, a mediator of oxygen delivery, and kinetics. Forty‐nine healthy adults (23 ± 3 years; 72 ± 13 kg; 1.80 ± 0.08 m) performed multiple repeat transitions to moderate‐ and heavy‐intensity exercise. Electrocardiography, impedance cardiography, and pulmonary gas exchange parameters were measured throughout; time domain measures of heart rate variability were subsequently derived. The parameters describing the dynamic response of , cardiac output () and RMSSDRR were determined using a mono‐exponential model. During heavy‐intensity exercise, the phase II τ of was significantly correlated with the τ of RR (r = 0.36, P < 0.05), Q (r = 0.67, P < 0.05), and RMSSDRR (r = 0.38, P < 0.05). The τ describing the rise in Q explained 47% of the variation in τ, with 30% of the rate of this rise in Q explained by the τ of RR and RMSSDRR. No relationship was evident between kinetics and those of Q, RR, or RMSSDRR during moderate exercise. Vagal withdrawal kinetics support the concept of a centrally mediated oxygen delivery limitation partly regulating kinetics during heavy‐, but not moderate‐, intensity exercise.     

One-year aerobic interval training in outpatients with schizophrenia: A randomized controlled trial

Although aerobic interval training (AIT) is recognized to attenuate the risk of cardiovascular disease (CVD) and premature mortality, it appears that it rarely arrives at patients’ doorsteps. Thus, this study investigated 1-year effects and feasibility of AIT delivered with adherence support in collaborative care of outpatients with schizophrenia. Forty-eight outpatients (28 men, 35 [31-38] (mean [95% confidence intervals]) years; 20 women, 36 [30-41] years) with schizophrenia spectrum disorders (ICD-10) were randomized to either a collaborative care group provided with municipal transportation service and training supervision (walking/running 4 × 4 minutes at ~90% of peak heart rate; HR_peak) 2 d wk⁻¹ at the clinic (TG) or a control group (CG) given 2 introductory AIT sessions and advised to continue training. Directly assessed peak oxygen uptake () increased in the TG after 3 months (2.3 [0.6-4.4] mL kg⁻¹ min⁻¹, Cohen's d = 0.33[−4.63 to 4.30], P = 0.04), 6 months (2.7 [0.5-4.8] mL kg⁻¹ min⁻¹, Cohen's d = 0.42[−4.73 to 4.11], P = 0.02) and 1 year (4.6 [2.3-6.8] mL kg⁻¹ min⁻¹, Cohen's d = 0.70[−4.31 to 4.10], P < 0.001) compared to the CG. One-year cardiac effects revealed higher HR_peak (7 [2-11] b min⁻¹, Cohen's d = 0.34[−8.48 to 8.65], P = 0.01), while peak stroke volume tended to be higher (0.9 [−0.2 to 2.0] mL b⁻¹, Cohen's d = 0.35[−1.62 to 2.01], P = 0.11) in the TG compared to the CG. Conventional risk factors (body weight, waist circumference, blood pressure, and lipids/glucose) remained unaltered in both groups. One-year AIT adherence rates were 15/25 (TG; different from CG: P < 0.001) and 0/23 (CG). AIT was successfully included in long-term collaborative care of outpatients with schizophrenia and yielded improved , advocating this model for aerobic capacity improvement and CVD risk reduction in future treatment.     

Peak oxygen uptake cut‐points to identify children at increased cardiometabolic risk – The PANIC Study

We aimed to develop cut‐points for directly measured peak oxygen uptake () to identify boys and girls at increased cardiometabolic risk using different scaling methods to control for body size and composition. Altogether 352 children (186 boys, 166 girls) aged 9‐11 years were included in the analyses. We measured V?O_2peak directly during a maximal cycle ergometer exercise test and lean body mass (LM) by bioelectrical impedance. We computed a sex‐ and age‐specific cardiometabolic risk score (CRS) by summing important cardiometabolic risk factors and defined increased cardiometabolic risk as >1 standard deviation above the mean of CRS. Receiver operating characteristics curves were used to detect V?O_2peak cut‐points for increased cardiometabolic risk. Boys with V?O_2peak <45.8 mL kg body mass (BM)^?1 min^?1 (95% confidence interval [CI] = 45.1 to 54.6, area under the curve [AUC] = 0.86, P < 0.001) and <63.2 mL kg LM^?1 min^?1 (95% CI =52.4 to 67.5, AUC = 0.65, P = 0.006) had an increased CRS. Girls with V?O_2peak <44.1 mL kg BM^?1 min^?1 (95% CI = 44.0 to 58.6, AUC = 0.67, P = 0.013) had an increased CRS. V?O_2peak scaled by BM^?0.49 and LM^?0.77 derived from log‐linear allometric modeling poorly predicted increased cardiometabolic risk in boys and girls. In conclusion, directly measured <45.8 mL kg BM^?1 min^?1 among boys and <44.1 mL kg BM^?1 min^?1 among girls were cut‐points to identify those at increased cardiometabolic risk. Appropriately controlling for body size and composition reduced the ability of cardiorespiratory fitness to identify children at increased cardiometabolic risk.     

An interdisciplinary examination of attentional focus strategies used during running gait retraining

The aim was to investigate the biomechanical, physiological, and perceptual responses to different motor learning strategies derived to elicit a flatter foot contact. Twenty‐eight rearfoot‐striking recreational runners (age 24.9 ± 2.8 years; body mass 78.8 ± 13.6 kg; height 1.79 ± 0.09 m) were matched by age, mass, and height and assigned to one verbal cue group: internal focus of attention (IF), external focus of attention (EF), and a clinically derived condition (CLIN) incorporating an IF followed by an EF statement. Participants completed two treadmill runs at 10 km h^?1 for 6 minutes each: normal running (control) followed by the experimental condition (IF, EF, or CLIN). Lower limb kinematics, oxygen consumption (), and central and peripheral ratings of perceived exertion (RPE) were recorded for each run. Compared to the control condition, foot angle was reduced in the IF (difference = 5.86°, d = 2.58) and CLIN (difference = 3.00°, d = 1.31) conditions, but unchanged in the EF condition (difference = 0.33°, d = 0.14), while greater knee flexion at initial contact in the EF and CLIN conditions was observed (difference = ?5.19°, d = 1.97; difference = ?3.66°, d = 1.39, respectively). A higher was observed in the CLIN condition (difference = ?4.56 mL kg^?1 min^?1, d = 2.29), but unchanged in the IF (difference = ?1.87 mL kg^?1 min^?1, d = 0.94) and EF conditions (difference = ?0.37 mL kg^?1 min^?1, d = 0.19). All experimental conditions increased central and peripheral RPE (difference = ?1.08, d = 0.54 and difference = ?2.39, d = 1.33, respectively). Providing gait retraining instructions using an internally directed focus of attention was the most effective way to target specific changes in running kinematics, with no detrimental effect on physiological responses. Yet, perceptual effort responses increased regardless of the type of cue provided.     

Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: A pilot study

This pilot study investigated whether a 10‐week running program (10wkRP), which reduced the oxygen cost of running, affected resultant ground reaction force (GRF), leg axis alignment, joint moment characteristics, and gear ratios. Ten novice, female runners completed a 10wkRP. Running kinematics and kinetics, in addition to oxygen consumption () during steady‐state running, were recorded pre‐ and post‐10wkRP. decreased (8%) from pre‐10wkRP to post‐10wkRP. There was a better alignment of the resultant GRF and leg axis at peak propulsion post‐10wkRP compared with pre‐10wkRP (10.8 ± 4.9 vs 1.6 ± 1.2°), as the resultant GRF vector was applied 7 ± 0.6° (P = 0.008) more horizontally. There were shorter external ankle moment arms (24%) and smaller knee extensor moments (23%) at peak braking post‐10wkRP. The change in was associated with the change in alignment of the resultant GRF and leg axis (r_s = 0.88, P = 0.003). As runners became more economical, they exhibited a more aligned resultant GRF vector and leg axis at peak propulsion. This appears to be a self‐optimization strategy that may improve performance. Additionally, changes to external ankle moment arms indicated beneficial low gear ratios were achieved at the time of peak braking force.     

Exercise performance increase in smokeless tobacco‐user athletes after overnight nicotine abstinence

The use of nicotine administered through smokeless tobacco (snus) has increased among athletes. The purpose of this study was to investigate the ergogenic effects of snus on aerobic performance during exercise until exhaustion in athletes after abstinence or satiety nicotine conditions. The study utilized a randomized, controlled, within‐subject design experiment. Sixteen male snus‐user athletes completed an exercise until exhaustion at a constant load of their 80% of (calculated by a maximal incremental test) in two separate sessions, corresponding to nicotine conditions: 12‐hour overnight abstinence and satiety. A portion of 1 g of snus (~8 mg/g of nicotine) was administered 25 minutes before each experimental test. In each session, time to exhaustion (TTE), global rating of perceived exertion, cardiovascular and metabolic responses, and muscle and cerebral oxygenation were measured. Nicotine and cotinine analysis confirmed session conditions (abstinence or satiety). Snus induced a significant increase (+13.1%) of TTE following abstinence (24.1 ± 10.7 minutes) compared to satiety condition (20.9 ± 8.0 minutes; P = 0.0131). The baseline values revealed that abstinence of snus induced significant increase in the oxygenation of the muscular tissues (+4%), in metabolic values and in cardiovascular parameters, when compared to satiety condition. Our results indicate an increase of exercise performance (+13.1% TTE) due to snus administration in an abstinence condition. Considering that twelve hours of abstinence from snus‐contained nicotine affected metabolic, cardiovascular and muscular tissue oxygenation, we suggest that snus administration at test time might relieve these withdrawal changes and yield an increase in time to exhaustion.     

Glucose response to exercise in the post‐prandial period is independent of exercise intensity

This study investigated the acute glucose response to low‐intensity, moderate‐intensity, and high‐intensity interval exercise compared to no‐exercise in healthy insufficiently active males using a four‐arm, randomized, crossover design. Ten males (age: 37.3 ± 7.3 years, BMI : 29.3 ± 6.5 kg·m⁻²) completed four 30‐minute interventions at weekly intervals comprising low‐intensity exercise (LIE ) at ~35% O₂R, moderate‐intensity exercise (MIE ) at ~50% O₂R, high‐intensity interval exercise (HIIE ) at ~80% O₂R, and a no‐exercise control. Participants performed cycle ergometer exercise 30 minutes after finishing breakfast. Glucose response was assessed using a continuous glucose monitor under free‐living conditions with dietary intake replicated. A significant effect for intensity on energy expenditure was identified (P  < .001) with similar energy cost in MIE (mean ± SD : 869 ± 148 kJ) and HIIE (806 ± 145 kJ ), which were both greater than LIE (633 ± 129 kJ). The pattern of glucose response between the interventions over time was different (P  = .02). Glucose was lower 25 minutes into each of the HIIE , MIE and LIE trials respectively (mean difference ± SD : −0.7 ± 1.1; −0.9 ± 1.1; −0.6 ± 0.9 mmol·L⁻¹; P  < .05) than in the no‐exercise trial. Glucose response was not different between exercise intensities (P  > .05). Twenty‐four‐hour AUC was not affected by exercise intensity (P  = .75). There was a significant effect for exercise enjoyment (P  = .02), with LIE (69 ± 4) preferred less than HIIE (mean ± SD : 84 ± 14; P  = .02), MIE (73 ± 5; P  = .03), and no‐exercise (75 ± 4; P  = .03). Exercise at any intensity 30 minutes after a meal affects glycemic regulation equally in insufficiently active males. Moderate to vigorous exercise intensities were preferred, and therefore, the exercise guidelines appear appropriate for the prevention of cardiometabolic disease.     

Sex differences in fitness and cardiac function during exercise in adolescents with chronic fatigue

Females demonstrate less robust Frank‐Starling mechanism with respect to cardiac preload than males at rest. We asked whether this phenomenon would also affect cardiac performance during exercise. We hypothesized that stroke volume (SV ) response to exercise would be more limited in deconditioned females such that cardiac output would be mainly rate dependent, compared with males. We conducted a chart audit of clinical exercise tests performed by adolescents with chronic fatigue. Oxygen uptake () was measured breath‐by‐breath at rest and during cycle ergometry, while cardiac output was measured by acetylene rebreathing at rest plus 2‐3 subthreshold workloads. SV response was analyzed in two ways: after normalization for body surface area (SV index, SVI ) and as percentage change from resting values. Among 304 adolescents (78% females) with chronic fatigue, 189 (80%) of 236 females and 52 (76%) of 68 males were deconditioned (peakO₂ <90% predicted). Heart rate trajectory during exercise was steeper for unfit than fit females, 70 vs 61 beat·min⁻¹ per L·min⁻¹ , (P =.003); but not for males, 47 vs 42 beat·min⁻¹ per L·min⁻¹ (P =.23). The highest measured SVI did not differ between unfit vs fit females (42.8 vs 41.5 mL·m⁻², P =.39) while fit males showed larger SV during exercise than their unfit peers (highest SVI 55.9 vs 48.0 mL·m⁻², P =.014). Both qualitative and quantitative sex differences exist in SV responses to exercise among chronically fatigued adolescents, suggesting volume loading may be more efficacious in girls.