Influence of training load on upper respiratory tract infection incidence and antigen‐stimulated cytokine production

This study examined the effect of training load on upper respiratory tract infection (URTI) incidence in men and women engaged in endurance‐based physical activity during winter and sought to establish if there are training‐associated differences in immune function related to patterns of illness. Seventy‐five individuals provided resting blood and saliva samples for determination of markers of systemic immunity. Weekly training and illness logs were kept for the following 4 months. Comparisons were made between subjects (n = 25) who reported that they exercised 3–6 h/week (LOW), 7–10 h/week (MED) or ≥ 11 h/week (HIGH). The HIGH and MED groups had more URTI episodes than the LOW group (2.4 ± 2.8 and 2.6 ± 2.2 vs 1.0 ± 1.6, respectively: P < 0.05). The HIGH group had approximately threefold higher interleukin (IL)‐2, IL‐4 and IL‐10 production (all P < 0.05) by antigen‐stimulated whole blood culture than the LOW group and the MED group had twofold higher IL‐10 production than the LOW group (P < 0.05). Other immune variables were not influenced by training load. It is concluded that high levels of physical activity are associated with increased risk of URTI and this may be related to an elevated anti‐inflammatory cytokine response to antigen challenge.     

Heritability estimates of endurance‐related phenotypes: A systematic review and meta‐analysis

The aim of this study was to clarify heritability estimates for endurance‐related phenotypes and the underlying factors affecting these estimates. A systematic literature search was conducted for studies reporting heritability estimates of endurance‐related phenotypes using the PubMed database (up to 30 September 2016). Studies that estimated the heritability of maximal oxygen uptake (), submaximal endurance phenotypes, and endurance performance were selected. The weighted mean heritability for endurance‐related phenotypes was calculated using a random‐effects model. A total of 15 studies were selected via a systematic review. Meta‐analysis revealed that the weighted means of the heritability of absolute values and those adjusted for body weight and for fat‐free mass were 0.68 (95% CI : 0.59‐0.77), 0.56 (95% CI : 0.47‐0.65), and 0.44 (95% CI : 0.13‐0.75), respectively. There was a significant difference in the weighted means of the heritability of across these different adjustment methods (P  < .05). Moreover, there was evidence of statistical heterogeneity in the heritability estimates among studies. Meta‐regression analysis revealed that sex could partially explain the heterogeneity in the heritability estimates adjusted by body weight. For submaximal endurance phenotypes and endurance performance, the weighted mean heritabilities were 0.49 (95% CI : 0.33‐0.65) and 0.53 (95% CI : 0.27‐0.78), respectively. There was statistically significant heterogeneity in the heritability estimates reported among the studies, and we could not identify the specific factors explaining the heterogeneity. Although existing studies indicate that genetic factors account for 44%‐68% of the variability in endurance‐related phenotypes, further studies are necessary to clarify these values.     

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.     

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.     

Influence of hydration status on thermoregulation and cycling hill climbing

PURPOSE: Although dehydration can impair endurance performance, a reduced body mass may benefit uphill cycling by increasing the power-to-mass ratio. This study examined the effects of a reduction in body mass attributable to unreplaced sweat losses on simulated cycling hill-climbing performance in the heat. METHODS: Eight well-trained male cyclists (mean +/- SD: 28.4 +/- 5.7 yr; 71.0 +/- 5.9 kg; 176.7 +/- 4.7 cm; VO2peak: 66.2 +/- 5.8 mL x kg(-1) x min(-1)) completed a maximal graded cycling test on a stationary ergometer to determine maximal aerobic power (MAP). In a randomized crossover design, cyclists performed a 2-h ride at 53% MAP on a stationary ergometer, immediately followed by a cycling hill-climb time-to-exhaustion trial (88% MAP) on their own bicycle on an inclined treadmill (8%) at approximately 30 degrees C. During the 2-h ride, they consumed either 2.4 L of a 7% carbohydrate (CHO) drink (HIGH) or 0.4 L of water (LOW) with sport gels to match for CHO content. RESULTS: After the 2-h ride and before the hill climb, drinking strategies influenced body mass (LOW -2.5 +/- 0.5% vs HIGH 0.3 +/- 0.4%; P < 0.001), HR (LOW 158 +/- 15 vs HIGH 146 +/- 15 bpm; P = 0.03), and rectal temperature (T(re): LOW 38.9 +/- 0.2 vs HIGH 38.3 +/- 0.2 degrees C; P = 0.001). Despite being approximately 1.9 kg lighter, time to exhaustion was significantly reduced by 28.6 +/- 13.8% in the LOW treatment (LOW 13.9 +/- 5.5 vs HIGH 19.5 +/- 6.0 min, P = 0.002), as was the power output for a fixed speed (LOW 308 +/- 28 vs HIGH 313 +/- 28 W, P = 0.003). At exhaustion, T(re) was higher in the LOW treatment (39.5 vs HIGH 39.1 degrees C; P < 0.001), yet peak HR, blood lactate, and glucose were similar. CONCLUSION: Exercise-induced dehydration in a warm environment is detrimental to laboratory cycling hill-climbing performance despite reducing the power output required for a given speed.     

Two weeks of repetitive gut‐challenge reduce exercise‐associated gastrointestinal symptoms and malabsorption

Debilitating gastrointestinal symptoms is a common feature of endurance running and may be exacerbated by and/or limit the ability to tolerate carbohydrate intake during exercise. The study aimed to determine whether two weeks of repetitive gut‐challenge during running can reduce exercise‐associated gastrointestinal symptoms and carbohydrate malabsorption. Endurance runners (n =18) performed an initial gut‐challenge trial (GC 1) comprising 2‐hour running exercise at 60% VO _2max (steady state) while consuming a formulated gel‐disk containing 30 g carbohydrates (2:1 glucose‐fructose, 10% w/v ) every 20 minutes, followed by a 1‐hour running effort bout. Gastrointestinal symptoms, feeding tolerance, and breath hydrogen (H₂) were determined along the gut‐challenge trial. After GC 1, participants were randomly assigned to a blinded carbohydrate (CHO , 90 gCHO  hour⁻¹) or placebo (PLA , 0 gCHO  hour⁻¹) gut‐training group. This comprised of consuming the group‐specific feeding intervention during 1‐hour running exercise at 60% VO _2max equivalent, daily over a period of two weeks. Participants then repeated the gut‐challenge trial (GC 2). In GC 2, a reduced gut discomfort (P =.012), total (P =.009), upper‐ (P =.015), and lower‐gastrointestinal (P =.008) symptoms, and nausea (P =.05) were observed on CHO , but not PLA . Feeding tolerance did not differ between GC 1 and GC 2 on CHO and PLA . H₂ peak was attenuated in GC 2 (6±3 ppm) compared to GC 1 (13±6 ppm) on CHO (P =.004), but not on PLA (GC 1 11±7 ppm, and GC 2 10±10 ppm). The effort bout distance was greater in GC 2 (12.3±1.3 km) compared with GC 1 (11.7±1.5 km) on CHO (P =.035) only. Two weeks of repetitive gut‐challenge improve gastrointestinal symptoms and reduce carbohydrate malabsorption during endurance running, which may have performance implications.     

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.     

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.     

Effects of reduced‐volume of sprint interval training and the time course of physiological and performance adaptations

This study sought to determine the time course of training adaptations to two different sprint interval training programmes with the same sprint: rest ratio (1:8) but different sprint duration. Nine participants (M: 7; F: 2) were assigned to 15‐second training group (15TG) consisting of 4‐6 × 15‐second sprints interspersed with 2‐minute recovery, whereas eight participants (M: 5; F: 3) were assigned to 30‐second training group (30TG) consisting of 4‐6 × 30 second sprints interspersed with 4‐minute recovery. Both groups performed their respective training twice per week over 9 weeks and changes in peak oxygen uptake () and time to exhaustion (TTE) were assessed every 3 weeks. Additional eight healthy active adults (M: 6; F: 2) completed the performance assessments 9 weeks apart without performing training (control group, CON). Following 9 weeks of training, both groups improved (15TG: 12.1%; 30TG: 12.8%, P<.05) and TTE (15TG: 16.2%; 30TG: 12.8%, P<.01) to a similar extent. However, while both groups showed the greatest gains in at 3 weeks (15TG: 16.6%; 30TG: 17.0%, P<.001), those in TTE were greatest at 9 weeks. CON did not change any of performance variables following 9 weeks. This study demonstrated that while the changes in cardiorespiratory function plateau within several weeks with sprint interval training, endurance capacity (TTE) is more sensitive to such training over a longer time frame in moderately‐trained individuals. Furthermore, a 50% reduction in sprint duration does not diminish overall training adaptations over 9 weeks.     

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.     

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.     

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.     

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.     

Dose-response effects of ingested carbohydrate on exercise metabolism in women

PURPOSE: The effect of different quantities of carbohydrate (CHO) intake on CHO metabolism during prolonged exercise was examined in endurance-trained females. METHOD: On four occasions, eight females performed 2 h of cycling at approximately 60% .VO2max with ingestion of beverages containing low (LOW, 0.5 g.min(-1)), moderate (MOD, 1.0 g.min(-1)), or high (HIGH, 1.5 g.min(-1)) amounts of CHO, or water only (WAT). Test solutions contained trace amounts of [U-13C] glucose. Indirect calorimetry combined with measurement of expired 13CO2 and plasma 13C enrichment enabled calculation of exogenous CHO, liver-derived glucose, and muscle glycogen oxidation during the last 30 min of exercise. RESULTS: The highest rates of exogenous CHO oxidation were observed in MOD, with no further increases in HIGH (peak rates of 0.33 +/- 0.02, 0.50 +/- 0.03, and 0.48 +/- 0.05 g.min(-1) for LOW, MOD, and HIGH, respectively; P < 0.05 for LOW vs MOD and HIGH). Endogenous CHO oxidation was lowest in MOD (0.99 +/- 0.06, 0.82 +/- 0.08, 0.70 +/- 0.07, and 0.89 +/- 0.09 g.min(-1); P < 0.05 for MOD vs all other trials). Compared with WAT, CHO ingestion reduced liver glucose oxidation during exercise by approximately 30% (P < 0.05 for WAT vs all CHO). Differential rates of muscle glycogen oxidation were observed with different CHO doses (0.57 +/- 0.07, 0.53 +/- 0.08, 0.41 +/- 0.07, and 0.60 +/- 0.09 g.min(-1) for WAT, LOW, MOD, and HIGH respectively; P < 0.05 for MOD vs HIGH). CONCLUSION: In endurance-trained women, the highest rates of exogenous CHO oxidation and greatest endogenous CHO sparing was observed when CHO was ingested at moderate rates (1.0 g.min(-1), 60 g.h(-1)) during exercise.     

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.     

Dose‐response effects of exercise on bone mineral density and content in post‐menopausal women

Exercise is one of the most widely used non‐pharmacological strategies to prevent bone resorption during menopause. Given the detrimental consequences of bone demineralization, the purpose of this study was to examine the effects of prescribing different exercise volumes on bone mineral density and content in previously inactive, post‐menopausal women during a 12‐month intervention and 1 year after intervention completion. Four hundred post‐menopausal women were randomized to either 150 min/wk (MODERATE dose group) or 300 min/wk (HIGH dose group) of aerobic exercise. Total bone mineral density (g/cm²) and bone mineral content (g) were assessed at baseline, 12 months (end of the intervention) and 24 months (follow‐up) using whole body dual‐energy X‐ray absorptiometry. At 12 months, mean bone mineral density among women in the HIGH dose group was estimated to be 0.006 g/cm² (95% CI: 0.001‐0.010; P = 0.02) higher than that of women randomized to the MODERATE dose group. At 24 months, the mean difference between groups remained statistically significant, indicating higher mean bone mineral density among women in the HIGH dose group (0.007 g/cm²; 0.001‐0.001; P = 0.04). No significant differences between groups were found at any time point for bone mineral content. In an exploratory analysis, women who completed more min/wk of impact exercises had significantly higher mean levels of bone mineral density at 12 months compared to baseline (0.006 g/cm², 95% CI: 0.006‐0.012; P = 0.03). These findings suggest that higher volumes of exercise, especially impact exercise, lead to a smaller decline in total bone mineral density, which may remain following intervention completion.     

Strength training improves double‐poling performance after prolonged submaximal exercise in cross‐country skiers

The purpose of this study was to investigate the effects of adding strength training with or without vibration to cross‐country (XC ) skiers’ endurance training on double‐poling (DP ) performance, physiological, and kinematic adaptations. Twenty‐one well‐trained male XC ‐skiers combined endurance‐ and upper‐body strength training three times per week, either with (n = 11) or without (n = 10) superimposed vibrations for 8 weeks, whereas eight skiers performed endurance training only (CON ). Testing included 1RM in upper‐body exercises, work economy, neural activation, oxygen saturation in muscle, and DP kinematics during a prolonged submaximal DP roller ski test which was directly followed by a time to exhaustion (TTE ) test. TTE was also performed in rested state, and the difference between the two TTE tests (TTE _diff) determined the ability to maintain DP performance after prolonged exercise. Vibration induced no additional effect on strength or endurance gains. Therefore, the two strength training groups were pooled (STR , n = 21). 1RM in STR increased more than in CON (P  <  .05), and there were no differences in changes between STR and CON in any measurements during prolonged submaximal DP . STR improved TTE following prolonged DP (20 ± 16%, P  <  .001) and revealed a moderate effect size compared to CON (ES  = 0.80; P  =  .07). Furthermore, STR improved TTE _diff more than CON (P  =  .049). In conclusion, STR superiorly improved 1RM strength, DP performance following prolonged submaximal DP and TTE _diff, indicating a specific effect of improved strength on the ability to maintain performance after long‐lasting exercise.     

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.     

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.     

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.