Medicine and Science in Sports and Exercise最新文献

Purpose: To examine the effects of 24-h manipulations in energy availability (EA), through altering energy intake (EI) or exercise energy expenditure (EEE), on sleep characteristics and nocturnal heart rate variability (HRV).

Methods: Twenty endurance athletes (10 females, 10 males) undertook five 24-h periods of EA manipulation, separated by 8 d, in a randomized Latin square design. Following 24 h of standardized high EA (45 kcal·kg -1 FFM·d -1 ), athletes then followed a diet providing low EA (15 kcal·kg -1 FFM·d -1 ) either with/without exercise (LEA EX/REST ), high EA (45 kcal·kg -1 FFM·d -1 ) with/without exercise (HEA EX/REST ), and excess EA (75 kcal·kg -1 FFM·d -1 ) without exercise (GEA). Sleep and overnight HRV were assessed using Somfit and Oura ring devices, respectively, pre- and post-EA manipulation.

Results: Total sleep duration was extended by 53-61 min following LEA EX versus non-exercise conditions: GEA ( P = 0.002), HEA REST ( P = 0.003), and LEA REST ( P = 0.020). Time in bed was also increased during LEA EX compared with GEA ( P = 0.006) and HEA REST ( P = 0.023), but without alterations to sleep efficiency between conditions ( P = 0.613). Sleep onset latency increased by 8 min following LEA REST compared with GEA ( P = 0.012), whereas there were no other alterations to objective/subjective sleep characteristics between conditions (all P > 0.05). There was no difference in overnight HRV following the 24-h EA manipulation ( P > 0.05). However, mean overnight HR was lower following LEA REST and HEA REST (-4 ± 3 and -2 ± 3 bpm), compared with LEA EX (+1 ± 3 bpm), HEA EX (0 ± 3 bpm), and GEA (0 ± 3 bpm, all P < 0.01). There was no difference between sexes in the response to EA manipulation across all variables.

Conclusions: Twenty-four hours of exercise-induced LEA extended total sleep time, whereas diet-induced LEA reduced mean overnight HR. The responses to EA manipulations did not differ between sexes.

Purpose: We tested the overarching hypothesis that the expended rate of work above critical power ( W ' Balance) during all-out whole-body exercise is related to a decline in prefrontal cortex (PFC) oxygenation secondary to an organized systemic outstripping of muscle O 2 supply relative to O 2 demand.

Methods: We concomitantly measured ( n = 16 males) skeletal muscle O 2 saturation (vastus lateralis near-infrared spectroscopy (NIRS); %S m O 2 ), pulmonary O 2 uptake (V̇O 2 ), and hemoglobin (Hb) differential (∆[O 2 Hb - HHb]) as an index of PFC O 2 mismatch ( pfc O 2 ) via functional NIRS bilaterally in the ventrolateral (VLPFC), dorsolateral (DLPFC), and orbitofrontal (OFC) cortices during brief all-out cycling exercise (highest instantaneous power for 3 min).

Results: All-out exercise evoked significant changes in %S m O 2 (∆ -28.8% ± 14.1%), V̇O 2 (∆27.7% ± 10.3%), and global pfc O 2 (∆ -7.6% ± 4.8%). Decreases in regional pfc O 2 were greater in the VLPFC (∆ -10.9 ± 6.1 μM) versus DLPFC (∆ -4.8 ± 4.5 μM) or OFC (∆ -5.9 ± 4.2 μM). Spatiotemporal analysis by O 2 measurement location revealed a steep rate of change transition phase followed by a maximal sustaining plateau, and progression of this pattern occurred sequentially first in muscle (~13 s) → pulmonary (~44 s) → PFC (~80 s). Transition phase O 2 indices were strongly correlated with the rate of W ' Balance expended (muscle, R2 = 0.91; pulmonary, R2 = 0.997; PFC, R2 = 0.968), with crossover between regional O 2 mismatches occurring at the same % W ' Balance (end muscle = 71% vs start pulmonary = 65%, P = 0.56; end pulmonary = 26% vs start PFC = 30%, P = 0.83) and end PFC transition phase occurring at complete depletion of W' (end PFC = -0.9%).

Conclusions: We conclude that whole-body all-out exercise tolerance may arise from a progressive O 2 mismatch from skeletal muscle to the brain.

Peak neuromuscular power and endurance are distinct qualities of dynamic exercise performance. Dynamometry is used to assess peak neuromuscular power, often during performance across a single joint, for example, isotonic or isokinetic torque, whereas aptitude for endurance exercise may be inferred by measurement of critical power/speed or cardiopulmonary exercise testing to determine, for example, gas exchange threshold (GET), maximum oxygen uptake (V̇O 2max ), and exercise economy. Specificity is a critical component of any training program, but oversimplification of the specificity principle has contributed to the view that training adaptations to increase peak neuromuscular power or the ability to endure high power outputs are mutually exclusive, due to (i) differences in the types of motor units recruited and their patterns of activation and (ii) induction of distinct, antagonistic molecular signaling pathways in response to resistance and endurance exercise training (the "interference effect").This review explores evidence for reciprocation between peak neuromuscular power and endurance performance in sport, aging, and among general and clinical populations. We also review the molecular events that mediate peak neuromuscular power and endurance training adaptations and their interactions. Finally, we describe the musculo-cardio-pulmonary exercise test (mCPET) to demonstrate that peak neuromuscular power and aerobic mediators of endurance performance are less polar opposites and more willing partners.

Purpose: To investigate the relationship between muscle (co-) activation time series and lower extremity stiffness (leg stiffness [ Kleg ], vertical stiffness [ Kvert ], and joint quasi-stiffness) during running in male recreational runners using statistical parametric mapping (SPM).

Method: Twenty-nine male recreational runners (age: 21 ± 1.17 yr, height: 1.80 ± 0.06 m, weight: 72.1 ± 9.91 kg) ran at 10 and 12 km·h -1 , while kinematic data, ground reaction forces, and surface electromyography signals from nine muscles were collected. SPM analyzed the temporal correlation between muscle (co-) activation time series and lower extremity stiffness across gait cycles.

Results: Higher soleus activation during the initial propulsion phase ( r = 0.506-0.552, 14.5%-21.2% of the gait cycle) and higher gastrocnemius lateralis activation during the mid-stance phase ( r = 0.504-0.527, 12.5%-17.5% of the gait cycle) showed large positive correlations with greater Kleg at 12 km·h -1 . Large correlations were also found between greater Kvert at 12 km·h -1 and higher soleus activation during the initial propulsion phase ( r = 0.508-0.622, 16.5%-24.3% of the gait cycle) and higher gastrocnemius lateralis activation during the mid-stance phase ( r = 0.507-0.601, 9.70%-20.5% of the gait cycle). Vastus lateralis activation during the propulsion phase was moderately to largely negatively correlated with ankle joint quasi-stiffness ( r = -0.595 to -0.464, 30.1%-37.9% of the gait cycle).

Conclusion: Higher ankle plantar flexor activation contributes to greater lower extremity stiffness regulation during stance, particularly during higher speeds. Furthermore, unilateral and distal muscles exhibited a more important role than bilateral and proximal muscles in regulating lower extremity stiffness. The knee extensors primarily regulated ankle joint quasi-stiffness during propulsion at lower speeds.

Purpose: Guardian Cap usage is growing among youth, college, and professional football players. Little on-field data exist describing Guardian Cap effectiveness, with combined published evidence based on less than 1000 Guardian Cap impacts. Our objective was to compare on-field head impact biomechanics (magnitude, location, frequency) between college football athletes wearing a Guardian Cap and teammates not wearing a Guardian Cap during practices and games throughout a season.

Methods: Fifty-four participants from two institutions were enrolled. Eleven (20.4%) wore a Guardian Cap for all contact practices, and 43 (79.6%) did not wear a Guardian Cap for one season. Instrumented mouthguards recorded on-field head impact kinematics. Impact magnitude (linear mixed effects models), frequency, and location (generalized linear mixed models) were analyzed.

Results: A total of 7509 impacts were recorded, including 1379 impacts (18.4%) when the Guardian Cap was worn. There were no significant effects of Guardian Cap use for any impact magnitude outcome ( P ≥ 0.127) or impact frequency ( P = 0.508). The odds of a facemask impact relative to other locations were 36.2% lower among those wearing the Guardian Cap relative to nonwearers ( P = 0.014). The odds of a rear impact relative to other locations were 151.6% greater among those wearing the Guardian Cap relative to nonwearers ( P = 0.001).

Conclusions: The Guardian Cap had no on-field effect on head impact magnitude or frequency, but impact location patterns presented between wearers and nonwearers, suggesting that Guardian Cap usage could influence how players use their head during collisions. Our findings partially align with other published data. The effect of Guardian Cap use on other factors we did not explore (e.g., injury epidemiology, clinical injury management) warrants consideration in the context of the data we present.

Purpose: Integrating musculoskeletal (MSK) modeling with inertial measurement units (IMUs) offers a promising approach for analyzing joint and muscle function during locomotion. This study examined the validity of combining IMUs, MSK modeling, and inverse dynamics to estimate lower-limb joint moments and hamstring musculotendon (MT) mechanics during treadmill running at varying speeds.

Methods: Eighteen healthy young adults ran on a treadmill at 70% (5.21 ± 0.62 m·s -1 ), 80% (5.96 ± 0.71 m·s -1 ), 85% (6.33 ± 0.76 m·s -1 ), 90% (6.70 ± 0.80 m·s -1 ), 95% (7.07 ± 0.84 m·s -1 ), and 100% (7.44 ± 0.89 m·s -1 ) of their maximal sprinting speed. Kinematic data were simultaneously collected using both an optical motion capture (OMC) system (Vicon) and an IMU system (Xsens), whereas electromyographic data recorded hamstring activity. MSK modeling was applied to both kinematic measurements to calculate lower-limb joint moments and hamstring MT mechanics, with estimated muscle activations validated against the electromyographic data.

Results: IMU-based estimations closely matched OMC-based calculations, with coefficient of multiple correlations exceeding 0.85 for hip and knee joint moments during swing and 0.95 for hamstring MT kinematics across full stride cycles at all speeds. MT force estimations varied among hamstring muscles, with semimembranosus showing the highest agreement (0.96 < coefficient of multiple correlation < 0.98) across all speeds. Linear mixed models showed for each 1 m·s -1 speed increase, root mean square errors between the two systems increased by less than 0.25 N·m for joint moments and 0.05 body weight for hamstring MT forces.

Conclusions: IMU-MSK integration is a valid alternative to OMC for estimating sagittal-plane joint moments and hamstring MT mechanics during treadmill running, although differences in peak hip moment during terminal swing warrant caution in field-based applications.

Purpose: This study aimed to assess the effect of ingesting a single bolus of hydrolyzed collagen or free amino acids on myofibrillar and muscle connective protein synthesis rates.

Methods: In a randomized, double-blind, parallel design, 45 young male ( n = 21) and female ( n = 24) adults (age, 23 ± 3 yr; BMI, 22.3 ± 2.2 kg·m -2 ) received intravenous infusions with L-[ ring - 13 C 6 ]-phenylalanine. After unilateral resistance exercise, participants ingested either 30 g hydrolyzed collagen (COLL, n = 15), 30 g free amino acids reflecting the collagen amino acid profile (AA, n = 15), or a noncaloric placebo (PLA, n = 15). Blood and muscle tissue samples were collected over 6 h to assess myofibrillar and muscle connective protein synthesis rates and associated signaling responses.

Results: Both collagen and free amino acid ingestion substantially increased circulating plasma amino acids concentrations and affected collagen turnover proteins. Collagen and free amino acid ingestion did not significantly increase myofibrillar protein synthesis rates in the rested (0.039 ± 0.011, 0.037 ± 0.010, and 0.036 ± 0.015%·h -1 in PLA, COLL, and AA, respectively) or the exercised (0.049 ± 0.010, 0.048 ± 0.011, and 0.045 ± 0.013%·h -1 ) leg ( P > 0.05). Similarly, both collagen and free amino acid ingestion did not significantly increase muscle connective protein synthesis rates in the rested (0.065 ± 0.014, 0.063 ± 0.017, and 0.061 ± 0.025%·h -1 in PLA, COLL, and AA, respectively) or the exercised (0.098 ± 0.023, 0.092 ± 0.028, and 0.085 ± 0.024%·h -1 ) leg ( P > 0.05).

Conclusions: The ingestion of a single bolus of collagen hydrolysate or free amino acids substantially increases circulating amino acids concentrations, particularly glycine, but does not further increase myofibrillar or muscle connective protein synthesis rates at rest or during recovery from exercise in healthy, recreationally active young men and women.

Purpose: Individuals with chronic ankle instability (CAI) are believed to rely more heavily on visual input during postural control due to impaired somatosensory function; however, the neural mechanisms underlying sensory reweighting in CAI are not well understood. This study explored the neural and behavioral correlates of increased visual reliance in CAI through functional connectivity (FC) analysis.

Methods: This cross-sectional study enrolled 37 patients with CAI and 36 healthy individuals. Participants underwent postural stability assessments using the single-leg stance test, both with their eyes open and closed. Traditional and modified Romberg ratios were calculated. Resting-state functional magnetic resonance imaging was used to estimate FC between the superior parietal cortex (SPC) and visual, sensorimotor, and cerebellar regions, as well as the coefficient of variation of these FCs.

Results: Compared with healthy individuals, patients with CAI displayed significantly higher visual reliance, as indicated by the traditional and modified Romberg ratios of sway length (Cohen's d = 0.47-0.57). Patients with CAI also exhibited stronger FC between the SPC and higher-level visual cortices (Cohen's d = 0.56-0.62) and more unstable coefficient of variation for FC between the SPC and the cerebellar anterior lobe (Cohen's d = 0.64). Subregion analysis revealed that variability in FC between subregions I-IV of the cerebellar anterior lobe and anterior lateral area 7 of the SPC was negatively correlated with the modified Romberg ratio in the anterior-posterior direction ( r = -0.35) among the patients.

Conclusions: The study revealed high visual reliance, strong yet variable SPC-based connections with visual cortices, and variable SPC-based connections with the cerebellum among patients with CAI, suggesting that neural changes associated with sensory reweighting mechanisms underlie increased visual reliance during postural stability.

Background: Longitudinal monitoring of blood parameters is used in sports drug testing within the hematological module of athlete's biological passport to detect alterations that may indicate blood doping. Glucocorticoids (GC) can act in an early stage of erythropoiesis stimulating the self-renewal of burst-forming unit erythroid and, therefore, might affect the hematological parameters.

Objective: The aim of the present work was to evaluate the effect of repeated oral doses of GC on the hematological passport.

Methods: Dexamethasone (DEX) was administered to healthy volunteers using a multi-dose oral treatment (2 mg/12 h for 5 d, n = 8 males). A control group with four male volunteers that did not receive the DEX treatment was included in the study. Blood samples were collected on different days before administration to set baseline values, and post-administration samples were collected up to day 8 from the first dose. All the parameters included in the hematological passport were measured using a Sysmex XN instrument and were used to estimate the hemoglobin mass and plasma volume using a multiparametric model. Variations in all parameters were statistically evaluated and compared with the physiological variations of the control group.

Results: A significant increase in reticulocyte-related parameters, along with a marked reduction in OFF score, was observed in the DEX group, particularly 48-72 h after the last dose. Hemoglobin concentration showed a transient decrease during the treatment, and Abnormal Blood Profile Score exhibited isolated fluctuations without a consistent pattern. By contrast, hemoglobin mass remained stable throughout the study. The control group showed no relevant changes over time, with all hematological parameters remaining remarkably stable.

Conclusions: Our results show that multiple oral doses of DEX affect the erythropoiesis, and therefore, they can lead to atypical hematological profiles. Additional studies are necessary to evaluate the effect in hemoglobin longer after administration.

Aim: We examined bench press adaptations to three widely used strength training methods: maximal strength training (MST), hypertrophy training (HT), and explosive strength training (EST). To reflect how these methods are typically applied by practitioners, MST and EST were volume matched, whereas HT was performed at higher volume.

Methods: Sixty-three moderately trained subjects (32 males, 31 females) were assigned into 8 wk of MST, HT, EST, or control (CON), three sessions per week. MST performed 4 × 4 repetitions bench press at ≥85% of one-repetition maximum (1RM). HT performed 3 × 8-12 repetitions at ∼70%-80% of 1RM. EST performed 4 × 6-7 repetitions bench press throws at 40% of 1RM. Maximal, explosive, and endurance strength characteristics were assessed, as well as muscle hypertrophy.

Results: 1RM increased more after MST (+21.5%) and HT (+17.9%) compared with EST (+5.9%) and CON (all P ≤ 0.001). Rate of force development (RFD) at 50% of 1RM increased more after MST (+58.4%) and HT (+38.9%) compared with CON ( P ≤ 0.001 and P ≤ 0.05, respectively). Mean propulsive velocity (MPV) increased more after MST and HT compared with CON across all loads (20%-80% of 1RM), and more than EST at 80% and 60% (all P ≤ 0.05-0.001). MST increased MPV more than EST at 40% of 1RM ( P ≤ 0.05). Δ1RM correlated with ΔMPV at all loads of the load-velocity (L-v) profile ( r = 0.40-0.56, P ≤ 0.001).

Conclusion: MST and HT were more effective than EST for improving maximal strength and concentric velocity against moderate and high loads. At low loads, EST was not more effective than MST and HT, despite high degree of velocity specificity. Changes in muscle strength appear to be more important than velocity specificity to increase performance across the L-v profile.