Medicine and Science in Sports and Exercise最新文献

Purpose: Human skeletal muscle has the profound ability to hypertrophy in response to resistance training (RT). However, this has a high energy and protein cost and is presumably mainly restricted to recruited muscles. It remains largely unknown what happens with nonrecruited muscles during RT. This study investigated the volume changes of 17 recruited and 13 nonrecruited muscles during a 10-wk single-joint RT program targeting upper arm and upper leg musculature.

Methods: Muscle volume changes were measured by manual or automatic 3D segmentation in 21 RT novices. Subjects ate ad libitum during the study and energy and protein intake were assessed by self-reported diaries.

Results: Posttraining, all recruited muscles increased in volume (range: +2.2% to +17.7%, P < 0.05), whereas the nonrecruited adductor magnus (mean: -1.5% ± 3.1%, P = 0.038) and soleus (-2.4% ± 2.3%, P = 0.0004) decreased in volume. Net muscle growth ( r = 0.453, P = 0.045) and changes in adductor magnus volume ( r = 0.450, P = 0.047) were positively associated with protein intake. Changes in total nonrecruited muscle volume ( r = 0.469, P = 0.037), adductor magnus ( r = 0.640, P = 0.002), adductor longus ( r = 0.465, P = 0.039), and soleus muscle volume ( r = 0.481, P = 0.032) were positively related to energy intake. When subjects were divided into a HIGH or LOW energy intake group, overall nonrecruited muscle volume (-1.7% ± 2.0%), adductor longus (-5.6% ± 3.7%), adductor magnus (-2.8% ± 2.4%), and soleus volume (-3.7% ± 1.8%) decreased significantly ( P < 0.05) in the LOW but not the HIGH group.

Conclusions: To our knowledge, this is the first study documenting that some nonrecruited muscles significantly atrophy during a period of RT. Our data therefore suggest muscle mass reallocation, that is, that hypertrophy in recruited muscles takes place at the expense of atrophy in nonrecruited muscles, especially when energy and protein availability are limited.

Purpose: To determine if individuals chronically (>1 yr) prescribed antihypertensive medications have a normal BP response to peak exercise compared with unmedicated individuals.

Methods: Participants included 2555 adults from the Ball State Adult Fitness Longitudinal Lifestyle STudy cohort who performed a peak treadmill exercise test. Participants were divided into groups by sex and antihypertensive medication status. Individuals prescribed antihypertensive medications for >1 yr were included. Exaggerated and blunted SBP within each group was categorized using the Fitness Registry and the Importance of Exercise: A National Database (FRIEND) and absolute criteria as noted by the American Heart Association.

Results: The unmedicated group had a greater prevalence ( P < 0.05) of blunted SBP responses, whereas the medicated group had a higher prevalence ( P < 0.05) of exaggerated SBP responses using both the FRIEND and absolute criteria. Peak SBP was higher ( P < 0.01) in medicated compared with unmedicated participants in the overall cohort when controlling for age and sex, but not after controlling for resting SBP ( P = 0.613), risk factors ( P = 0.104), or cardiorespiratory fitness ( P = 0.191). When men and women were assessed independently, peak SBP remained higher in the medicated women after controlling for age and resting SBP ( P = 0.039), but not for men ( P = 0.311). Individuals on beta-blockers had a higher peak SBP even after controlling for age, sex, risk factors, and cardiorespiratory fitness ( P = 0.022).

Conclusions: Individuals on antihypertensive medications have a higher peak SBP response to exercise. Given the prognostic value of exaggerated peak SBP, control of exercise BP should be considered in routine BP assessment and in the treatment of hypertension.

Purpose: To evaluate the significance of body surface area-to-mass ratio (BSA/mass) on the heat-tolerance test (HTT) results. We hypothesized that individuals defined as heat tolerant (HT) would have on average higher BSA/mass compared to heat intolerant (HI) individuals.

Methods: A retrospective reanalysis of the HTT results of 517 soldiers (age: 18-38 yrs., M/F: 96/4%), who were tested by the Israel Defense Forces (IDF) HTT protocol. The criterion for heat tolerance in the current analysis was a rectal temperature (Tre) plateau during the second hour of the test. A logistic regression analysis to evaluate the predictive power of BSA/mass for heat intolerance was performed; the spline model was applied to show the odds for heat intolerance across BSA/mass.

Results: In men BSA/mass of HI individuals was lower than HT individuals (248 ± 19 vs. 262 ± 18 cm2/kg, p < 0.01, d = 0.76). In women a similar trend was noted but with no statistical significance between HT and HI groups. The odd ratio for heat intolerance for every unit increase in BSA/mass was 0.97 (CI 95% 0.95-0.99). The spline model plateaued above BSA/mass of 270 cm2/kg.

Conclusions: The results imply that body-core temperature responses to a standard exercise-heat stress (fixed external work rate and climatic conditions) are influenced by BSA/mass. More specifically, lack of a steady state in Tre (indicating heat intolerance) was more likely to occur with every unit decrease in BSA/mass. These findings contribute to a better understanding of the role of body anthropometry in the response to a standard exercise-heat task that might have an implication on clinical decision-making about return to duty/play of soldiers, athletes and others who deemed to be identified as HI.

Introduction: Muscle activation during interruptions to prolonged sedentary time is a hypothesized mechanism underlying observed cardiometabolic benefits. We examined associations of quadriceps and hamstring muscle activity patterns with cardiometabolic risk markers and how these patterns varied between different sitting-interruption countermeasures.

Methods: Electromyographic (EMG) data (shorts) were gathered for 1 to 2 days from healthy adults in a free-living study (n = 172, age 40.9 ± 12.9, BMI 23.6 ± 1.3) and a laboratory-based study (n = 12, age 47.0 ± 7.7, BMI 30.0 ± 4.7). Patterns examined were average EMG (aEMG ;%EMGMVC); EMG activity duration (% above signal baseline 3 μV); and usual (weighted medians) EMG activity bout amplitude (%EMGMVC) and duration (s). In the free-living study, these were regressed against risk markers (waist; fat percentage; fasting plasma glucose [FPG];total cholesterol; HDL;LDL; triglycerides); in the laboratory study, EMG patterns for the muscle groups were compared between sitting and the active countermeasures.

Results: In the free-living study, lower extremity muscles displayed minimal overall activity, with hamstrings and quadriceps using only 2.6% and 2.0% of their capacity (%EMGMVC), respectively, and being active for 30% and 25% of the time. Higher hamstring aEMG and EMG activity duration were beneficially associated with waist, HDL and fat percentage (duration only) and a longer quadriceps usual EMG activity bout duration was beneficially associated with FPG. In the laboratory study, compared with prolonged sitting, active seated or upright active-interruption countermeasures modified these EMG patterns; brief (6 min) walking and simple resistance activities (SRA) were more beneficial than was a bout of standing (30 min) with the SRAs being the only intervention that matched daily aEMG levels.

Conclusions: Upright and physically active interruptions to sitting appear to be required to increase the typically low muscle engagement observed in free-living contexts, promoting muscle activity patterns that may help ameliorate cardiometabolic risk.

Purpose: To develop a new method that more closely represents the heavy-to-severe exercise domain boundary by evaluating the rates of blood lactate accumulation during the constant power output exercise bouts that are employed in the assessment of the maximal lactate steady state (MLSS).

Methods: Eight well-trained male cyclists completed five exercise tests of up to 30 min for determination of the traditional MLSS (MLSSTRAD) and a further four maximal tests for determination of critical power (CP). The rates of change of blood [lactate] between 10 min and the end of exercise in the MLSS tests were plotted against the corresponding power outputs and a two-segment linear regression model was used to identify individualised breakpoints in lactate accumulation vs. power output (MLSSMOD).

Results: MLSSMOD was significantly higher than MLSSTRAD (297 ± 41 vs. 278 ± 41 W; P < 0.001) but was not significantly different from CP (297 ± 41 W; P > 0.05); MLSSMOD and CP were closely aligned (r: 0.97; Bias: -0.52 W; SEE: 10 W; Limits of Agreement: -20 to 19 W). The rates of change of both blood [lactate] and V̇O2 were significantly greater, and exercise intolerance occurred before 30 min, at a power output slightly above MLSSMOD.

Conclusions: A novel method for evaluating blood lactate kinetics during a traditional MLSS protocol produces a modified MLSS that is not different from CP and better represents the heavy-to-severe exercise domain boundary.

Purpose: Energy deficiency decreases muscle protein synthesis (MPS), possibly due to greater whole-body essential amino acid (EAA) requirements and reliance on energy stores. Whether energy deficit-induced anabolic resistance is overcome with non-nitrogenous supplemental energy or if increased energy as EAA is needed is unclear. We tested the effects of energy as EAA or carbohydrate, combined with an EAA-enriched whey protein, on post-exercise MPS (%/h) and whole-body protein turnover (g protein/240 min).

Methods: 17 adults (mean ± SD; age: 26 ± 6 y, BMI: 25 ± 3 kg/m 2 ) completed a randomized, parallel study including two 5-d energy conditions (BAL, energy balance; DEF, -30 ± 3% energy requirements) separated by ≥7 d. Volunteers consumed EAA-enriched whey with added EAA (+EAA; 304 kcal, 56 g protein, 48 g EAA, 17 g carbohydrate, 2 g fat; n = 8) or added carbohydrate (+CHO; 311 kcal, 34 g protein, 24 g EAA, 40 g carbohydrate, 2 g fat; n = 9) following exercise. MPS and whole-body protein synthesis (PS), breakdown (PB), and net balance (NET; PS-PB) were estimated postexercise with isotope kinetics.

Results: MPS rates were greater in +EAA (0.083 ± 0.02) than +CHO (0.059 ± 0.01; P = 0.015) during DEF, but similar during BAL ( P = 0.45) and across energy conditions within treatments ( P = 0.056). PS rates were greater for +EAA (BAL, 117.9 ± 16.5; DEF, 110.3 ± 14.8) than +CHO (BAL, 81.6 ± 8.0; DEF, 83.8 ± 5.9 g protein/240 min; both P < 0.001), and greater during BAL than DEF in +EAA ( P = 0.045). PB rates were less in +EAA (8.0 ± 16.5) than +CHO (37.8 ± 7.6 g protein/240 min; P < 0.001), and NET was greater in +EAA (106.1 ± 6.3) than +CHO (44.8 ± 8.5 g protein/240 min; P < 0.001).

Conclusions: These data suggest that supplementing EAA-enriched whey protein with more energy as EAA, not carbohydrate, maintains postexercise MPS during energy deficit at rates comparable to those observed during energy balance.

Purpose: Modifying foot progression angle (FPA), the angle between the line from the heel to the second metatarsal head and the line of progression, can reduce peak knee adduction moment (pKAM). However, determining the optimal FPA that minimizes pKAM without inducing unnatural walking patterns can be challenging. This study investigated the FPA-pKAM relationship using a robotic stepping trainer to assess the feasibility of determining the optimal FPA based on this relationship. Additionally, it examined knee moments during stepping with three different FPAs, as stepping is a recommended exercise for knee osteoarthritis (KOA) rehabilitation.

Methods: Twenty-six asymptomatic individuals stepped on a robotic stepping trainer, which measured 6-axis footplate-reaction forces/torques and three-dimensional (3-D) ankle kinematics to determine external knee moments. The robot rotated the footplates slowly (~0.5 deg/sec) between 10°-toe-out and 10°-toe-in while participants stepped continuously, unaware of the footplate rotations. The slope of pKAM-FPA relationship during continuous stepping was determined. Peak 3-D knee moments were compared between the 10°-toe-in, 0°-FPA, and 10°-toe-out FPAs with repeated-measure ANOVA. Multiple linear regression determined the covariates that predicted pKAM during stepping.

Results: Eighteen participants had lower pKAM and KAM impulse with 10°-toe-in than 10°-toe-out (p < 0.001) and 0°-FPA (p < 0.001 and p = 0.008, respectively) (called toe-in responders). Conversely, eight participants reduced pKAM and KAM impulse with 10°-toe-out compared to 0°-FPA (p < 0.001, p = 0.017) and 10°-toe-in (p = 0.026, p = 0.004) (called toe-out responders). A linear pKAM-FPA relationship was determined for each individual, and its slope (the pKAM rate with FPA) was positive for toe-in responders (p < 0.01) and negative for toe-out responders (p = 0.02). Regression analysis revealed that smaller pKAM with toe-in in toe-in responders was explained by increased tibia medial tilt, tibia internal rotation, footplate-reaction lateral force, footplate-reaction anterior force, and decreased footplate-reaction internal rotation torque.

Conclusions: Individuals may exhibit different responses to FPA modification during stepping. The slope and intercept of the linear pKAM-FPA relationship can be determined for individual subjects. This allows for a targeted pKAM reduction through guided FPA positioning and potentially offers subject-specific precision KOA rehabilitation.

Methods: 28 adults (16 males and 12 females) aged 30 ± 10 y [peak oxygen uptake (V̇O2peak): 59 ± 11 ml·kg-1·min-1] completed three experimental trials in a randomized, crossover, and double-blinded manner. Participants ingested either 0.3 (KE-LO) or 0.6 (KE-HI) g·kg-1 body mass of KE or a flavour-matched placebo (PLAC) ~30 min prior to exercise. Exercise involved a 3-minute warm-up, three 5-minute stages at fixed incremental workloads corresponding to 75%, 100%, and 125% of individual ventilatory threshold, followed by a ramp protocol to volitional exhaustion to determine peak power output (PPO).

Results: Venous blood [ß-hydroxybutyrate], the major circulating ketone body, was higher after KE ingestion compared to PLAC (KE-HI: 3.0 ± 1.1 ≥ KE-LO: 2.3 ± 0.6 ≥ PLAC: 0.2 ± 0.1 mM; all p ≤ 0.001. There were no differences between conditions in the primary outcome exercise economy, nor gross efficiency or delta efficiency, when analyzed over the entire submaximal exercise period or by stage. Heart rate and ventilation were higher in KE-HI and KE-LO compared to PLAC when assessed over the entire submaximal exercise period and by stage (all p ≤ 0.05). PPO after the ramp was lower in KE-HI compared to both KE-LO and PLAC (329 ± 60 vs 339 ± 62 and 341 ± 61 W respectively; both p < 0.05) despite no difference in V̇O2peak.

Conclusions: KE ingestion did not change indices of exercise efficiency but increased markers of cardiorespiratory stress during submaximal incremental cycling and reduced PPO.

Purpose: Given the rising burden of heart failure (HF), stratification of patients at increased risk for adverse events is critical. We aim to compare the predictive value of various maximal and submaximal cardiopulmonary exercise test (CPET) variables for adverse events in patients with HF.

Methods: 237 patients with HF (66 [58-73] years, 30% women, 70% HF with reduced ejection fraction) completed a CPET and had five years of follow-up. Baseline characteristics and clinical outcomes (all-cause mortality, major adverse cardiovascular events, and cardiovascular-related hospitalization) were extracted from electronic patient files. Receiver operating characteristics curves for maximal (e.g. peak VO2) and submaximal CPET variables (e.g. VE/VCO2 slope, cardiorespiratory optimal point (COP), VO2 at anaerobic threshold) were compared using the Akaike Information Criterion (AIC) method, whereas their calibration was assessed.

Results: 103 participants (43%) reached the composite endpoint, and 55 (23%) died. Percent predicted peak VO2 was the best predictor for adverse outcomes (AIC: 302.6) followed by COP (AIC: 304.3), and relative peak VO2 (mL/(kg·min), AIC: 304.4). Relative peak VO2 (AIC: 217.1) and COP (AIC: 224.4) were also among the three best predictors for mortality, together with absolute peak VO2 (ml/min, AIC: 220.5). A good calibration between observed and predicted event rate was observed for these variables.

Conclusions: Percent predicated and relative peak VO2 had the best predictive accuracy for adverse events and mortality, but the submaximal COP had a non-inferior predictive accuracy for adverse events in patients with HF. These findings highlight the potential of submaximal exercise testing in patients with HF.

Purpose: To investigate the temporal effects of ~1,800 m altitude exposure and energy availability (EA) manipulation on resting metabolic rate (RMR).

Methods: Twenty elite female race walkers underwent a 3-week training camp at an altitude of ~1,800 m. During the first two weeks, athletes consumed a high EA (HEA) diet of 45 kcal·kg fat free mass (FFM) -1 ·day -1 . During the final week, half the athletes consumed a low EA (LEA) diet of 15 kcal·kg FFM -1 ·day -1 while the others continued on a HEA diet. Athletes followed individualized training plans throughout the study. To assess the effect of altitude on RMR, athletes in the HEA group had RMR measured at baseline (~580 m) prior to altitude exposure (Pre-alt), at 36-hours (36 h-alt), 2 weeks (Wk2-alt) and 3 weeks into altitude exposure (Wk3-alt), and at 36 hours post-altitude exposure at ~580 m (36 h-post). To assess the effect of LEA exposure on RMR while at altitude, athletes in the LEA group underwent RMR measurements at Pre-alt and before (Wk2-alt) and after the 7-days of LEA (Wk3-alt).

Results: Compared to Pre-alt, the RMR of HEA athletes was increased at 36 h-alt (+5.3 ± 3.1%; p = 0.026) and Wk2-alt (+4.9 ± 4.9%; p = 0.049), but was no longer elevated at Wk3-alt (+1.7 ± 4.2%; p = 0.850). The RMR of HEA athletes at 36 h-post was lower than all timepoints at altitude (p < 0.05) but was not different from Pre-alt (-3.9 ± 7.2%; p = 0.124). The 7-day period of LEA exposure at altitude did not affect RMR (p = 0.347).

Conclusions: RMR was transiently increased with ~1,800 m altitude exposure in female athletes and was unaffected by short-term LEA. However, the altitude-induced increase was small (~25-75 kcal/day) and was unlikely to have clinically significant implications for daily energy requirements.