Medicine and Science in Sports and Exercise最新文献

Introduction: Traditional neuromuscular fatigue assessments are not task-specific and are unable to characterize neuromuscular performance decline during dynamic whole-body exercise. This study used interleaved maximal isokinetic cycling efforts to characterize the dynamics of the decline in neuromuscular performance during ramp-incremental (RI) cycle ergometry exercise to intolerance.

Methods: Eleven young healthy participants (10 male/1 female) performed two RI cycle ergometry exercise tests to intolerance: 1) RI exercise with peak isokinetic power (Piso) at 80 rpm measured at baseline and immediately at intolerance from a maximal ~6 s effort, and 2) RI exercise where additional Piso measurements were interleaved every 90 s to characterize the decline in neuromuscular performance during the RI test. Muscle excitation was measured using EMG during all Piso assessments, and pulmonary gas exchange was measured throughout.

Results: Baseline Piso was 832 ± 140 W and RI exercise reduced Piso to 349 ± 96 W at intolerance ( P = 0.001), which was not different from flywheel power at intolerance (303 ± 96 W; P = 0.292). There was no reduction in Piso between baseline cycling and gas exchange threshold (GET; baseline Piso vs mean Piso below GET: 828 ± 146 vs 815 ± 149 W; P = 1.00). Piso fell progressively above GET until intolerance (Piso every 90 s above GET: 759 ± 139, 684 ± 141, 535 ± 144, 374 ± 117 W; each P < 0.05 vs baseline and mean Piso below GET). Peak muscle excitation (EMG) was also reduced only above GET (73% ± 14% of baseline, at intolerance; P < 0.05). However, the reduction in peak Piso preceded the reduction in peak muscle excitation.

Conclusions: The dynamics of the decline in neuromuscular performance (reduction in Piso and EMG) during RI exercise are consistent with known intensity-dependent metabolic and traditional pre-post neuromuscular fatigue responses to discrete bouts of constant-power exercise.

Purpose: To quantify the relative performance of step counting algorithms in studies that collect free-living high-resolution wrist accelerometry data and to highlight the implications of using these algorithms in translational research.

Methods: Five step counting algorithms (four open source and one proprietary) were applied to the publicly available, free-living, high-resolution wrist accelerometry data collected by the National Health and Nutrition Examination Survey (NHANES) in 2011-2014. The mean daily total step counts were compared in terms of correlation, predictive performance, and estimated hazard ratios of mortality.

Results: The estimated number of steps were highly correlated (median, 0.91; range, 0.77-0.98), had high and comparable predictive performance of mortality (median concordance, 0.72; range, 0.70-0.73). The distributions of the number of steps in the population varied widely (mean step counts range from 2453 to 12,169). Hazard ratios of mortality associated with a 500-step increase per day varied among step counting algorithms between HR = 0.88 and 0.96, corresponding to a 300% difference in mortality risk reduction ([1-0.88] / [1-0.96] = 3).

Conclusions: Different step counting algorithms provide correlated step estimates and have similar predictive performance that is better than traditional predictors of mortality. However, they provide widely different distributions of step counts and estimated reductions in mortality risk for a 500-step increase.

Introduction: Formulating individualized optimized jump training prescriptions based on the force-velocity profile has become popular, but its effectiveness has been contested. Such training programs have opposite effects on "maximal average force" and "maximal average shortening velocity," and we set out to investigate which training-induced changes in the neuromuscular system could cause such effects.

Methods: We used a musculoskeletal simulation model with four body segments and six muscle-tendon actuators to simulate vertical squat jumps with different loads. Independent input was muscle stimulation over time, which was optimized for maximal jump height. We determined the force-velocity profile for a reference model and investigated how it changed when we modified muscle properties and initial postures.

Results: We could not reproduce the reported training effects by realistically improving muscle properties (maximal force, shortening velocity, and rate of force development) or modifying initial postures of the model. However, the profile was very sensitive to gains in jump height at low loads but not high loads, or vice versa. Reaching maximal height in force-velocity profile jumps requires skill. We argued that submaximal performance in low-load or high-load jumps caused by lack of skill could be responsible for large imbalances in profiles before training. Differential skill training promoted by the individualized optimized approach could explain quick changes toward a balanced profile.

Conclusions: If the success of individualized optimized training studies is explained by selective skill improvements, training effects are unlikely to transfer to other tasks, and individualized optimized training will not be superior to other types of training.

Background: Sleeping at altitude is highly common in athletes as an integral part of altitude training camps or sport competitions. However, concerns have been raised because of expected negative effects on sleep quality, thereby potentially hampering exercise recovery and next-day exercise performance. We recently showed that ketone ester (KE) ingestion beneficially impacted sleep after strenuous, late evening exercise in normoxia, and alleviated hypoxemia. Therefore, we hypothesized that KE ingestion may be an effective strategy to attenuate hypox(em)ia-induced sleep dysregulations.

Methods: Eleven healthy male participants completed three experimental sessions including normoxic training and subsequent sleep in normoxia or at a simulated altitude of 3000 m while receiving either KE or placebo postexercise and presleep. Sleep was evaluated using polysomnography, whereas next-day exercise performance was assessed through a 30-min all-out time trial (TT 30' ). Physiological measurements included oxygen status, heart rate variability, ventilatory parameters, blood acid-base balance, and capillary blood gases.

Results: Hypoxia caused a ~3% drop in sleep efficiency, established through a doubled wakefulness after sleep onset and a ~22% reduction in slow wave sleep. KE ingestion alleviated the gradual drop in SpO 2 throughout the first part of the night, but did not alter hypoxia-induced sleep dysregulations. Neither KE nor nocturnal hypoxia affected TT 30' performance, but nocturnal hypoxia hampered heart rate recovery after TT 30' .

Conclusions: We observed that sleeping at a 3000 m altitude impairs sleep efficiency. Although this hypoxia-induced sleep disruption was too subtle to limit exercise performance, we for the first time indicate that sleeping at altitude might impair next-day exercise recovery. KE alleviated nocturnal hypoxemia only when SpO 2 values dropped below ~85%, but this did not translate into improved sleep or next-day exercise performance.

Purpose: Cigarette smoking (CS) induces systemic changes that impair cardiorespiratory and muscular function both at rest and during exercise. Although these abnormalities are reported in sedentary, middle-aged smokers (SM) with pulmonary disease, few and controversial studies focused on young, physically active SM at the early stage of smoking history. This study aimed at assessing the effect of CS on cardiorespiratory and metabolic response during an incremental test and the subsequent recovery in young, physically active SM without known lung or cardiovascular disease.

Methods: After pulmonary function evaluation, 12 SM (age: 22±2 yr; body mass: 75±8 kg; stature: 1.78±0.06 m; 12±4 cigarette per day for 6±2 yr; mean ± SD) and 12 non-SM (control group; age: 23±1 yr; body mass: 76±8 kg; stature: 1.79±0.08 m) matched for age and exercise habits underwent an exhaustive incremental step test (25 W/2 min) on a cycle ergometer. Pulmonary O 2 uptake (V̇O 2 ), expiratory ventilation (V̇ E ), heart rate ( fH ) responses and lactate concentration were assessed during the test and subsequent recovery.

Results: Despite similar static lung volumes, SM reported lower peak expiratory flow (-23%; P = 0.003) and maximal voluntary ventilation (-10%; P = 0.003). At submaximal exercise, no differences in the cardiorespiratory and metabolic were noted between the two groups. However, SM exhibited ventilatory ( P < 0.01) and lactate thresholds at lower work rates ( P = 0.01). At peak exercise, SM exhibited lower V̇O 2 (-8%; P = 0.02), mechanical power (-11%; P = 0.02), and V̇ E (-9%; P = 0.01). During recovery, SM showed longer time constants (τ) in V̇O 2 (+52%; P = 0.002), V̇ E (+19%; P = 0.027) and fH (+21%; P = 0.022) and smaller fH at 30 s of recovery (HRR30; -31%; P = 0.032).

Conclusions: These results are compatible with an early CS-related impairment of the cardiorespiratory and metabolic function even in young individuals with relatively short smoking history.

Purpose: Valgus load opens the medial elbow compartment, causing elongation of the ulnar collateral ligament (UCL) that can eventually lead to attenuation and failure. Ideally, the muscles surrounding the medial aspect of elbow joint should coordinate medial elbow compression to prevent the medial elbow compartment from opening and loading the UCL. This study aimed to determine whether baseball pitchers have sufficient elbow varus strength to unload the UCL during pitching.

Methods: Using an electromagnetic tracking device, we measured the peak elbow varus moment during pitches (fastball, slider, curveball, and changeup) by 14 professional and 8 collegiate pitchers. Elbow varus strength was measured with an isokinetic dynamometer system while the medial elbow joint space was monitored using ultrasonography. A paired t -test was used to compare the peak varus moment generated during pitching with the varus strength, and the relative intensity of muscular output required to unload the UCL was determined.

Results: Except for curveballs, the muscular varus strength (57.5 ± 9.2 N·m) was not significantly larger ( P = 0.165-0.853) than the peak varus moments during pitching (55.4 ± 13.0 N·m). Ten participants did not have sufficient muscular varus strength to completely unload the UCL from valgus loading when throwing fastballs and other pitch types. The relative intensity of muscular torque output required for stress shielding of the UCL ranged from 89.1% ±21.7% maximum voluntary isometric varus strength (MVIVS) for curveballs to 103.1% ±26.5% MVIVS for fastballs.

Conclusions: Our findings demonstrate that most of the valgus load on the elbow joint during pitching can be counteracted by the muscular varus moment, but valgus loading on the UCL is likely unavoidable in baseball pitching.

Purpose: The purpose of this project was to evaluate physical activity trends in individuals with Parkinson's disease (PD) over a 12-month period using continuous activity monitoring. Environmental (temperature) and cultural factors (represented by day of the week) were evaluated as potential external sources of variability. It was hypothesized that physical activity would decline over the course of 12 months. Further, it was hypothesized that participants would exhibit greater physical activity on warmer days and that the day of the week would have minimal impact on physical activity as many participants were no longer in the workforce.

Methods: Participants were part of the Usual and Customary Care arm ( N = 119) of the CYClical Lower Extremity Exercise Trial for Parkinson's disease-II (CYCLE-II) at the Cleveland Clinic and University of Utah. Participants wore a Garmin Vivofit4® device daily for 12 months. A linear mixed effects model was created to model daily steps over 12 months.

Results: Participants wore their activity monitors on 93% of study days. Steps per day declined by 6.1% over 12 months (95% confidence interval, 12.6% decline, 0.9% increase; P = 0.09). Steps per day were greater with warmer temperatures ( P < 0.001), plateauing and declining between 75°F to 85°F (24-29°C). Participants took fewer steps on Sunday; this daily difference was more pronounced for Utah participants, who took 25% fewer steps on Sundays compared with other weekdays ( P < 0.001).

Conclusions: Most individuals live with PD for decades, and interventions should address the expected annual decline in daily step count. Environmental and cultural factors impact daily step count and should be adjusted for in short- and long-term monitoring of physical activity in individuals with PD.

Introduction: Carbon plates have been used to increase running shoes' longitudinal bending stiffness (LBS), but their effect during a long duration run remains unknown. Our study aimed to identify the effect of LBS on energy cost of running (Cr), biomechanics, and fatigue during a half-marathon.

Methods: Thirteen well-trained male runners (half-marathon time <1 h 40) performed two half-marathons at 95% of the running speed associated with their second ventilatory threshold on two separate visits, with either high-LBS (HLBS) shoes, with carbon plates) or standard-LBS (SLBS) shoes. Before and after the half-marathon, Cr at 12 km·h -1 with both shoes (two 6-min bouts: Cr12) and ankle plantar flexor (PF) force were measured. During the half-marathon, running kinematics, shoe perceived comfort, and Cr were assessed.

Results: During Cr12 measurements before and after the half-marathon, HLBS was 1.0% ± 2.1% more economical than SLBS ( P < 0.001). During the half-marathon, Cr increased with running duration ( P = 0.048), but there was no distance×condition effect. HLBS increased contact time (+3%, P = 0.01), decreased metatarsophalangeal joint dorsiflexion (-9%, P = 0.01), and was perceived less comfortable than SLBS, independently from running duration. At the end of the half-marathon, HLBS shoes led to higher PF force loss (-20.0% ± 9.8% vs -13.3% ± 11.0%, P = 0.048).

Conclusions: Adding curved carbon plates in the running shoes slightly improved Cr during short running bouts at low intensity but not during a half-marathon. This discrepancy may be explained by day-to-day Cr variability and variation in shoe comfort. PF fatigue was higher with HLBS shoes, but the accentuated fatigue did not further impact the biomechanical perturbations induced by the plates. Our results suggest that carbon plates alone do not provide a significant advantage for half-marathon performance.

Purpose: Achilles tendinopathy is associated with altered tendon's morphological and mechanical properties, yet it is unclear whether these properties are reversed upon mechanical loading to promote tendon healing. This study aims to determine the extent to which pathological tendon's morphological and mechanical properties adapt throughout a 12-wk eccentric rehabilitation protocol.

Methods: Forty participants with midportion Achilles tendinopathy were recruited and participated in a 12-wk eccentric rehabilitation program. Function and symptoms were recorded through the Victorian Institute of Sports Assessment-Achilles (VISA-A) and hopping. The tendon's morphological (i.e., volume, midportion cross-sectional area (CSA) and anteroposterior (AP) diameter) and mechanical (i.e., stiffness, Young's modulus, and tendon nonuniform displacement) properties were measured at baseline and at 6 and 12-wk of the intervention.

Results: Significant functional improvements were observed, with VISA-A scores and hopping results showing marked improvements ( P < 0.001). Morphologically, no significant changes in volume, midportion CSA, or AP diameter were found, although a trend toward decreased CSA between 30% and 70% of tendon length was noted. Mechanically, significant increases in Achilles tendon stiffness ( P = 0.001) and Young's modulus ( P < 0.001) were observed over the course of the rehabilitation program. No differences in tendon nonuniform displacement were found after a 12-wk rehabilitation program.

Conclusions: These findings suggest that tendon adaptation in response to mechanical loading primarily involves changes in mechanical properties rather than morphology, highlighting the complexity and variability in tendon adaptation. Clinically, these mechanical properties could be considered in the load progression throughout rehabilitation as potentially higher strains will be induced when clinical improvements precede mechanical adaptations.

Introduction: Force plate systems are increasingly utilized in the armed forces that claim to identify individuals at risk of musculoskeletal injury. However, factors influencing injury risk scores from a force plate system (SpartaScience™) and the effects of experimental perturbations on these scores remain unclear.

Methods: Healthy males ( n = 823; 22.7 ± 3.9 yr) performed a countermovement jump (CMJ) on SpartaScience™ force plates. Multiple regression analysis was used to identify predictors of the system's proprietary Musculoskeletal (MSK) Health score, which were then experimentally perturbed. Twelve males (30.9 ± 4.3 yr) participated in a test-retest reliability study, performing three standard CMJs and one experimentally manipulated jump (50% effort) due to the observed relationship between the MSK Health score, vertical jump height, and body weight.

Results: The MSK Health score was negatively correlated with vertical jump height and positively with body weight ( R2 = 0.59, P < 0.001). Each inch increase in jump height decreased the MSK Health score by an average of 1.27 units (95% confidence interval, 1.17-1.36), whereas each pound of body weight increased it by 0.12 units (95% confidence interval, 0.11-0.13). Notably, 83% of participants in the reliability study improved their MSK Health score on the 50% effort jump.

Conclusions: The study revealed atypical relationships between MSK Health scores, vertical jump height, and body weight, with vertical jump height playing a majority role in predicting the principal output (MSK Health score). Findings indicated a higher injury risk with greater jump height but a lower risk with increased body weight. In addition, MSK Health scores paradoxically improved with lower effort (i.e., lower vertical jump height), which highlights the dangers of using undisclosed and unvetted algorithms for the prediction of health outcomes.