Medicine and Science in Sports and Exercise最新文献

Purpose: This study measured the time course mV̇O 2 max following both maximal and submaximal exercise.

Methods: Healthy male and female participants were tested ( n = 12 maximal and n = 8 submaximal exercise). A NIRS device was placed on the left medial gastrocnemius. Participants performed either 1 min of maximal, rapid (~2 Hz), or submaximal (~0.37 Hz) plantar flexion exercise on a custom pneumatic ergometer. mV̇O 2 max was measured before and immediately after exercise. mV̇O 2 max measurements consisted of four incomplete recovery curves of muscle metabolism taken after 30 s of electrical muscle stimulation except in the first post-exercise to be consistent with the use of pre-exercise trial. The four recovery curves were collected 50-, 156-, 260-, and 366-s postexercise, each producing an mV̇O 2 max rate constant.

Results: After maximal exercise, muscle acceleration decreased to 52 ± 18% ( P = 0.001) of prevalues. mV̇O 2 max was reduced from the pre-exercise mean at the first post-trial (2.16 ± 0.44 to 1.21 ± 0.52 min -1 , P < 0.001). The fourth trial showed recovery from the first (2.2 ± 0.46 min -1 vs 1.21 ± 0.52 min -1 , P < 0.001) and was not significantly different from pre-exercise values (2.2 ± 0.46 vs 2.16 ± 0.44 min -1 , P = 0.41). No change in acceleration or mV̇O 2 max was seen after submaximal exercise ( P > 0.05).

Conclusions: The 56.7% reduction in mV̇O 2 max supports the hypothesis that in young, healthy individuals, a minute of maximal exercise transiently impairs mV̇O 2 max, which then recovers within 6 min. The NIRS method shows promise in tracking time course changes in mV̇O 2 max and warrants further investigation of the transient effects of exercise on mV̇O 2 max.

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. In addition, it examined knee moments during stepping with three different FPAs, as stepping is a recommended exercise for knee osteoarthritis rehabilitation.

Methods: Twenty-six asymptomatic individuals stepped on a robotic stepping trainer, which measured six-axis footplate-reaction forces/torques and three-dimensional ankle kinematics to determine external knee moments. The robot rotated the footplates slowly (~0.5 deg·s -1 ) 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 three-dimensional knee moments were compared between the 10°-toe-in, 0°-FPA, and 10°-toe-out FPAs with repeated-measures 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 with 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 knee osteoarthritis rehabilitation.

Purpose: Cold water immersion (CWI) is the most effective treatment for exertional heat stroke (EHS). However, knowledge on core temperature response during CWI treatment and the relation with patient characteristics (i.e., sex, anthropometrics) is limited. Therefore, the current study aimed to examine the core temperature response (in °C) during CWI treatment of recreational athletes participating in large running events and investigate the impact of sex and anthropometric characteristics on the cooling rate (in °C·min -1 ).

Methods: This observational study includes 57 athletes ( n = 22 females; 39%) who suffered from EHS during an exercise event in the Netherlands. After admission to the medical facilities, a rectal temperature ( Trec ) probe was inserted and all clothing was removed before immersion in an ice bath (6.4 ± 1.6°C). Rectal temperature was continuously measured throughout treatment, and treatment was continued until Trec ≤ 38.9°C or based on the decision of the emergency physician.

Results: Initial Trec did not differ between males (41.3 ± 0.9°C) and females (41.2 ± 0.8°C, P = 0.83). A nonlinear response to CWI was observed, with the decrease in Trec beginning after 6 min of CWI. The decrease in Trec did not differ between both sexes (p time*sex = 0.96). The cooling rate did not differ between males (0.21 ± 0.15°C·min -1 ) and females (0.19 ± 0.08°C·min -1 , P = 0.55), and was not related to body mass, body surface area and body surface area to mass ratio (all P values >0.05).

Conclusions: We demonstrated that the cooling rate during CWI did not differ between men and women suffering from EHS, and that the Trec response to CWI is nonlinear and not dependent on anthropometric characteristics. This suggests that no sex differentiation is needed in the EHS treatment guidelines and confirms the necessity to continuously monitor Trec during treatment.

Introduction/purpose: The purpose of this study was to test the hypothesis that cardiovascular (CV) drift and associated decrements in maximal oxygen uptake (V̇O 2max ) are greater in high-fit compared with low-fit women during exercise at the same %V̇O 2max , but comparable at the same rate of metabolic heat production.

Methods: Six high-fit (HI) and six low-fit (LO) women cycled in 35°C for 15 or 45 min at the same relative intensity (60% V̇O 2max ; 15REL and 45REL) or fixed rate of heat production (500 W; 15FX and 45FX), immediately followed by a graded exercise test to measure V̇O 2max . The separate 15- and 45-min trials permitted measurements of V̇O 2max over the same time interval as CV drift.

Results: During 45REL, higher heat production in HI (496 ± 51 vs 364 ± 44 W in LO) resulted in greater end-exercise core temperature (38.7°C ± 0.4°C vs 38.2°C ± 0.1°C, P = 0.03), greater increases in HR (15 bpm (10%) vs 10 bpm (6%), P = 0.03) and decreases in stroke volume (11 mL per beat (16%) vs 5 mL per beat (8%), P = 0.001), and larger reductions in V̇O 2max (16% vs 5%, P = 0.04) compared with LO. During 45FX, temperature responses, CV drift, and decreased V̇O 2max were not different between groups (all P > 0.05), despite differences in %V̇O 2max (60% vs 75% for HI and LO, respectively).

Conclusions: We conclude metabolic heat production modulates the CV drift-V̇O 2max relationship, independent of fitness level. These results support previous findings showing the magnitude of CV drift is proportional to reductions in V̇O 2max .

Purpose: Altitude training is a common strategy used with the intent to increase hemoglobin mass (Hb mass ) in athletes. However, if the Hb mass is increased during altitude camps, it seems to decline rapidly upon returning to sea level. This study aimed to examine the efficacy of three weekly heat training sessions over a 3.5-wk period after a 3-wk altitude camp on the maintenance of Hb mass in elite cyclists.

Methods: Eighteen male cyclists (maximal oxygen consumption: 76 ± 5 mL·min -1 ·kg -1 ) underwent a 3-wk altitude training camp at ~2100 m above sea level. After the camp, participants were divided into one group performing three weekly heat sessions that were subtracted from their usual training (HEAT) while the other continuing usual training (CON). Training characteristics were recorded during the intervention, whereas hematological measurements were recorded before the camp as well as 2 d and 3.5 wk after the altitude camp.

Results: The 3-wk altitude camp led to an overall increase in total Hb mass of 4.1%. Afterward, HEAT maintained Hb mass (0.2%, P = 0.738), whereas CON group experienced a significant reduction (-3.3%, P < 0.001) (ΔHEAT vs ΔCON, P < 0.001). Moreover, HEAT increased plasma volume (PV) by 11.6% ( P = 0.007) and blood volume (BV) by 5.8% ( P = 0.007), whereas CON only showed an increase in PV (5.5%, P = 0.041). Exercise intensity and training load were not different between groups during the maintenance period.

Conclusions: This study suggests that incorporating three weekly heat training sessions into the usual training routine preserves a moderately increased Hb mass in elite cyclists after an altitude camp.

Methods: Twenty-eight adults (16 males and 12 females) aged 30 ± 10 yr (peak oxygen uptake (V̇O 2peak ): 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 flavor-matched placebo (PLAC) ~30 min before exercise. Exercise involved a 3-min warm-up, three 5-min 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 with 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 with 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 with both KE-LO and PLAC (329 ± 60 vs 339 ± 62 and 341 ± 61 W, respectively; both P < 0.05) despite no difference in V̇O 2peak .

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

Purpose: Exercise-nutrient timing is of interest for people with type 2 diabetes (T2D) as a potential method to optimize glycemic control. However, the optimal nutritional environment for exercise is not well understood over the long term. The Fasted Exercise for Type 2 Diabetes (FED) Trial compared 16 wk of fasted versus postprandial morning exercise on glycated hemoglobin (HbA1c) and liver proton density fat fraction (PDFF).

Methods: Twenty adults with T2D were recruited and randomized to complete exercise after an overnight fast versus after their morning meal. Participants walked three mornings per week, progressing to 180 min·wk -1 over 16 wk.

Results: Groups were balanced with five males and five females each. Sixteen participants completed the trial (8 in each group, 50% female). Age, HbA1c, and PDFF were 59.8 ± 9.0 yr, 7.2 ± 0.7%, and 9.3 ± 4.1%, respectively. On average, both groups completed 98% of their walking sessions but there was no change in HbA1c (-0.2%, P = 0.588). However, one participant from each group had changes in their glucose-lowering medication during the trial, and when excluded, the fasted training group had greater improvements in HbA1c compared with the postprandial group (-0.3% vs 0.0%, P = 0.033). There was no difference in changes in liver PDFF between groups (-1.6% vs 0.3%, P = 0.221) but visceral fat and intramuscular fat decreased to a greater extent after fasted exercise.

Conclusions: Although our study had a small sample size, it suggests that exercise after an overnight fast can have high adherence and represents an option for people with T2D to improve longer-term indicators of glycemia and ectopic fat depots.

Purpose: Interstructural release (ISR) procedure to skeletal muscles is believed to attenuate adhesion between neighboring muscles and alleviate subjective symptoms, including perceived stiffness and associated pain. However, objective evidence about the effect of ISR on the mechanical properties of the muscles is limited. The purpose of this study was to test the acute effect of ISR on the shear modulus of adjacent muscles. It was hypothesized that ISR applied to the border between synergistic muscles would acutely reduce the resting shear modulus of the involved muscle.

Methods: To assess the effect of ISR, the shear modulus of the resting peroneus longus (PL) and soleus (SOL) muscles was measured at various ankle joint positions (inversion/eversion) before and after interventions in nine nonsymptomatic male individuals (age: 21.9 ± 1.4 yr, height: 170 ± 6.6 cm, body mass: 64.3 ± 4.0 kg). Potential muscle activity during the measurement was assessed by recording surface electromyogram from these muscles. The interventions were ISR to the lower leg between the deep fascia of the PL and SOL and sham (massage).

Results: As the ankle joint position was passively varied toward inversion, the shear modulus increased substantially in PL and decreased moderately in SOL. Shear modulus of the proximal PL in the most inverted position increased acutely after ISR (by 11.4 ± 5.8%, P <0.001), but not after the sham, without any change in the amplitude of electromyogram.

Conclusions: These results provide objective evidence that the ISR procedure can acutely alter shear modulus, at least in a specific site in a resting muscle.

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 d 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;%EMG MVC ); EMG activity duration (% above signal baseline 3 μV); and usual (weighted medians) EMG activity bout amplitude (%EMG MVC ) and duration (s). In the free-living study, these were regressed against risk markers (waist, fat percentage, fasting plasma glucose, total cholesterol, high-density lipid cholesterol, low-density lipid cholesterol, 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 (%EMG MVC ), respectively, and being active for 30% and 25% of the time. Higher hamstring aEMG and EMG activity duration were beneficially associated with waist, high-density lipid cholesterol and fat percentage (duration only) and a longer quadriceps usual EMG activity bout duration was beneficially associated with fasting plasma glucose. 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: We investigated the effects of a 4-month intervention targeting sedentary behavior on sedentary time and physical activity level, clinical parameters, cardiometabolic risk factors, inflammatory markers, and health-related quality of life in postmenopausal women with rheumatoid arthritis.

Methods: This was a 4-month, parallel-group, randomized controlled trial ( ClinicalTrials.gov identifier: NCT03186924). One hundred and three postmenopausal rheumatoid arthritis patients were randomized (1:1) to either a newly developed intervention targeting sedentary behavior (Take a STAND for Health [TS4H]) or standard of care (SOC). Sedentary behavior (primary outcome) and physical activity levels, clinical parameters, anthropometric parameters and body composition, blood samples and oral glucose tolerance test, blood pressure, muscle function, and health-related quality of life were assessed at baseline (Pre) and after 4 months (Post). Between- and within-group differences were tested using linear mixed models following the intention-to-treat principle.

Results: Total sedentary time, time in prolonged sitting bouts, standing, and stepping did not change in either group (all P ≥ 0.337). No significant between- and within-group differences were detected for any of the clinical parameters, markers of cardiometabolic health and inflammation, and health-related quality of life variables (all P ≥ 0.136). Among responders in TS4H group (those who reduced sedentary time by ≥30 min·d -1 ), Pre to Post IL-10 concentrations tended to reduce (group-time: P = 0.086; estimated mean difference [EMD]: -12.0 pg·mL -1 [-23.5 to -0.6], P = 0.037) and general health (group-time: P = 0.047; EMD: 10.9 A.U. [-1.1 to 22.9], P = 0.086) and overall physical health tended to improve (group-time: P = 0.067; EMD: 7.9 A.U. [-0.9 to 16.6], P = 0.089).

Conclusions: TS4H did not change sedentary behavior, physical activity levels, clinical, cardiometabolic, inflammatory, or health-related quality of life outcomes. However, TS4H tended to reduce IL-10 levels and improve health-related quality of life in responders.