Purpose: Ectopic fat in non-adipose tissues is linked to higher chronic-disease risk. Using the UK Biobank, this study examined associations of device-measured physical activity (PA) and sedentary time with ectopic fat. Methods: Liver and pancreas proton density fat fraction (PDFF), and anterior-thigh skeletal muscle fat infiltration (MFI) were assessed by magnetic resonance imaging. Reallocations among accelerometer derived time spent sedentary and in light intensity PA (LPA), and moderate-to-vigorous intensity PA (MVPA) were examined using isotemporal substitution. Multi-variable linear regression was employed with stepwise adjustment for sex, age, height, socioeconomic factors, and counts of cancer and non-cancer illnesses. Sex*activity interaction terms were then added to the models, and sex-stratified analyses were conducted where interactions were significant. Results: The final sample comprised 9,213 participants with liver PDFF, 6,521 participants with pancreatic PDFF, and 9,197 participants with MFI (mean age ~64 years). Replacing 30 minutes of sedentary time with LPA was associated with lower ectopic fat, with relative percentage differences in fully adjusted models of -2.2% [-2.7%, -1.8%] for liver PDFF, 1.9% [-2.4%, -1.3%] for pancreas PDFF, and -0.5% [-0.7%, -0.4%] for MFI. Substituting sedentary time with MVPA showed greater differences (-9.9% [11.0%, 8.7%], 7.9% [-9.2%, -6.6%], and -3.6 % [-3.9%, -3.2%], respectively). Replacing LPA with MVPA was also associated with lower ectopic fat (-7.6% [-8.9%, -6.4%], -6.0% [7.5%, -4.6%], and -3.0% [-3.4%, -2.6%] for liver PDFF, pancreas PDFF, and MFI. Associations were stronger in females for liver and pancreas PDFF and MFI when sedentary time was replaced with LPA or MVPA. Conclusions: Reallocation of sedentary time or lower-intensity PA to higher intensity PA is linked to lower ectopic fat. These relationships are stronger in women than men.
Purpose: The aim of this study was to determine if the linear and nonlinear coefficients of the energy expenditure-walking speed relationship are influenced by body mass index (BMI; kg/m 2 ) and sex. Methods: Participants (n=182; 96 females) ages 18-60 yr walked at 0.89 m/s (2.0 mph), 1.34 m/s (3.0 mph), and 1.79 m/s (4.0 mph) for six min each while oxygen uptake (V̇O 2 ; mL/kg/min) was calculated via indirect calorimetry and converted to energy expenditure (EE; W/kg). Net W/kg was calculated by subtracting standing W/kg from gross W/kg. Polynomial random coefficient regression (PRCR) was employed to produce individual-level linear and quadratic coefficients to assess whether BMI influenced W/kg during walking. Net energy cost of walking (Cw; J/kg/m) was also determined for each walking speed. Results: Net W/kg and Cw were not significantly correlated with BMI at 0.89 m/s and 1.79 m/s, but were weakly inversely correlated (r 2 < 0.03) with BMI at 1.34 m/s. BMI was not significantly correlated with the linear coefficient for net or gross W/kg (both r = 0.07), but was weakly correlated with the quadratic coefficient for net (r = 0.17, P = 0.02) and gross (r = 0.16, P = 0.04) W/kg (r 2 < 0.03 for both). However, PRCR coefficients did not differ between normal weight BMI (n=32; 18.5-<25.0 kg/m 2 ), overweight (n=74; 25-<30.0 kg/m 2 ) and obese (n=76; > 30.0 kg/m 2 ) groups. Females had higher W/kg, but sex differences were eliminated after controlling for height. Conclusions: We conclude that BMI has little impact on the EE of walking at speeds between 0.89 m/s and 1.79 m/s, and that sex differences in walking EE are eliminated after controlling for height.
Purpose: Optimal healing after a tibia fracture depends on appropriate mechanical loading. Ground reaction force is often used as an indicator of expected tibia load, but it does not account for internal forces placed on the tibia from muscle contractions. Objectives of this study were to 1) characterize peak forces on the distal tibia during common exercises used for rehabilitation after lower extremity injury, 2) compare peak tibial force to peak ground reaction forces for each exercise, and 3) compare rank-ordered exercises based on tibial force to clinician expectations of tibial load. Methods: Participants (10 M/10 F) completed 16 rehabilitation exercises in standardized order while three-dimensional marker data and ground reaction forces were recorded synchronously. Physical therapists (n=12) completed a survey to rank the same exercises in order of expected tibial load. Compressive tibia force was estimated using a musculoskeletal model with ankle joint moment and ground reaction force as inputs. Exercises were ranked by peak tibial force and peak ground reaction force. Survey data were compiled to provide a clinician rank for each exercise. Results: The relationship between peak tibial force and ground reaction force was not consistent across exercises. Clinician ranking of exercises by tibial load differed from the model-estimated order of calculated tibia force. Conclusions: Ground reaction forces are not a suitable surrogate for estimated distal tibia force across exercises, which may result in under- or over-dosing of load relative to recovery trajectory. This study provides a reference data set of estimated tibial force that can support clinicians’ exercise prescription.
Purpose: Physical activity supports cognitive and brain health, however the biological mechanisms underlying these benefits remain unclear. This study investigated changes in salivary alpha-amylase (sAA), a marker of sympathetic nervous system activity, and salivary cortisol (CORT), reflecting hypothalamus-pituitary-adrenal (HPA) axis activity, as candidate mechanisms mediating the effects of acute exercise on brain function, cognition, and academic achievement in children. Methods: In a pre-post randomized crossover design, 104 children (ages 9-10) completed exercise, the Trier Social Stress Test for Children (TSST-C; active control), and seated rest (passive control) conditions, with neuroelectric activity (P3 amplitude and latency), attentional inhibition, and academic achievement as outcomes. Structural equation modeling was performed to examine sAA and CORT as mediators of the relationship between exercise and outcomes. Moderated mediation tested whether the magnitude of the sAA-mediated path varied as a function of pre-intervention baseline CORT. Results: Exercise led to lower sAA than both controls and lower CORT than the TSST-C, controlling for pre-intervention baselines. Post-exercise reductions in sAA mediated reductions in trial-to-trial reaction time variability (SDRT) on incongruent trials, indexing more consistent inhibitory control. Exercise effects on neuroelectric activity (P3 amplitude) varied with baseline CORT. Conclusions: This study is among the first to investigate the biological underpinnings of acute exercise-induced changes in cognition in children using molecular, behavioral, neuroelectric, and academic achievement measures. Findings implicate sAA-indexed sympathetic activity as a candidate mechanism through which acute exercise may support specific aspects of inhibitory control in children, reflected behaviorally as more consistent responding on trials requiring the upregulation of inhibitory control. These findings also suggest that individual differences in baseline HPA axis activity moderate exercise effects on neural markers of attentional inhibition.
PURPOSE:Cognitive-motor dual-task performance is prevalent in many sports and appears to be impaired during high-intensity exercise, in association with central fatigue and cerebral deoxygenation. However, the extent to which these responses differ between males and females remains unknown. METHODS:Forty-eight well-trained adults (16 females) performed an incremental cycling test with a sustained-attention Mackworth task. The protocol consisted of 3-min ramp stages (starting at 1 W·kg -1, +0.4 W·kg -1 per stage) until an "extremely strong" perceived exertion was achieved (Borg CR100, task-failure). At each stage, cognitive performance (Mackworth score), quadriceps isometric maximal voluntary contraction (IMVC), neuromuscular fatigue (peripheral: twitch force, Pt; central: voluntary activation, VA) and prefrontal oxygenation (near-infrared spectroscopy) was assessed. RESULTS:Both sexes reached similar normalised power output (~3.3±0.5 W·kg -1) and heart rate (~175±7 bpm) at task-failure (all P≥0.25). Mackworth score declined at task-failure (P=0.014), with no sex differences (males: -9±28%; females: -4±28%; P=0.56). Prefrontal oxygenation was lower in females versus males (-3.0±2.6%; P=0.031), while females exhibited reduced prefrontal total-haemoglobin at task-failure (-9.1±4.4 ∆µmol; P=0.016). IMVC and Pt declined more in males (all P≤0.014), whereas VA decreased similarly in both sexes (P=0.62), concomitant with comparable increased perceived exertion (P=0.73). CONCLUSIONS:Although high-intensity exercise similarly impaired sustained attention performance and VA, females conjointly exhibited reduced prefrontal total-haemoglobin and less peripheral fatigue for comparable perceived exertion. These results extend the understanding of women's reduced (primarily peripheral) fatigability to whole-body exercise under a challenging dual-task paradigm.
Objective: Most children in developed countries fail to meet public health recommendations for physical activity. This study identified home, parent and family factors that are associated with physical activity in a large and diverse sample of U.S. children. Methods: Field staff conducted structured interviews with child/parent dyads (n=5138, mean age (SD) =9.28 (2.65) years) sampled from 130 U.S. communities. Children and/or parents reported children’s participation in moderate to vigorous physical activities. Home, parent, neighborhood and child factors that were hypothesized to be associated with child physical activity were assessed. The study involved secondary analysis of data collected in 2013-2015. Data were analyzed in 2023-2025 using classification and regression trees (CART) to identify home-based factors that were cross-sectionally associated with children’s MVPA. Results: CART showed that children tended to be more physically active if they participated frequently in structured physical activity programs, rated themselves and their friends as physically active, and had parents who regularly provided transportation for them to be active. Conclusions: Future interventions to increase children’s physical activity should focus on promotion of children’s participation in structured physical activity programs and parental provision of transportation of children to physical activity programs.
INTRODUCTION:Body composition and anthropometric measurements are valuable for predicting health and performance outcomes. Three-dimensional body scanners provide a portable, cost-effective, and rapid method for collecting anthropometric and body composition metrics; however, their accuracy must be validated against clinical reference methods to ensure that the outputs are reliable and valid. METHODS:This study evaluated the reliability and validity of a portable 3D body scanner (Styku S100X) compared to manual anthropometry and dual-energy X-ray absorptiometry (DXA). Fifty participants (25 male, 25 female) underwent manual anthropometric assessments, two 3D full-body scans, and a full-body DXA scan. Reliability was assessed using intra-class correlations (ICC; k = 3, absolute agreement, two-way mixed-effects model), while validity was examined using Pearson's r correlations with manual anthropometry and DXA measurements. Data were stratified by sex, body mass index, body mass, stature, and age to provide exploratory insight into the potential influence of these factors on the 3D scanner's accuracy. For each group, mean difference with 95% CI, root mean square error (RMSE), and mean absolute percentage error (MAPE) were calculated. RESULTS:The 3D body scanner demonstrated excellent reliability for segment circumferences and body composition (ICC > 0.95, p < 0.001) and good to excellent reliability for segment lengths and widths (ICC = 0.80-0.97, p < 0.001). Segment circumference estimates showed very large to nearly perfect correlations with manual anthropometry (r = 0.78-0.99, MAPE < 8%), but length and width estimates did not accurately reflect ISAK-standard measurements due to differences in landmark identification (r = 0.09-0.81, MAPE: 6-42%). Lean mass estimates demonstrated the strongest agreement with DXA (r = 0.61-0.95, MAPE < 8%), whereas body fat percentage (MAPE: 11-29%), fat mass (MAPE: 11-29%), and android and gynoid fat mass (MAPE: 59-74%) showed poor agreement. CONCLUSIONS:These findings suggest that while the 3D scanner is suitable for tracking anthropometric and body composition measurements over time, body composition estimates (aside from lean mass) should not be considered accurate representations of an individual's body composition. Caution is advised when using 3D body scanner estimates for body composition assessment in clinical, sport, or fitness settings.
PURPOSE:This study examined the impact of pre-exercise caffeine supplementation on post-exercise torque reduction, an indirect marker of exercise-induced muscle damage (EIMD), while focusing on the changes in eccentric load induced by the ergogenic effects of caffeine. METHODS:In double-blind, crossover trials, 15 healthy young men ingested 6 mg/kg caffeine or placebo, followed by an eccentric exercise task at 30-120° of knee extension: 100 isokinetic eccentric maximal voluntary knee extensions in Study 1 (i.e., variable eccentric load by caffeine) and 100 isoload (fixed at 120% of concentric one-repetition maximum) eccentric leg extensions in Study 2 (i.e., invariable eccentric load by caffeine). Maximal voluntary isometric torque (MVIT) of the knee extensors, an indirect EIMD marker, was evaluated at 24 and 48 h after exercise. RESULTS:In Study 1, caffeine supplementation resulted in higher eccentric torques during exercise (P ≤ 0.001), but lower post-exercise MVITs (P < 0.001) than placebo. Conversely, in Study 2, there were no significant differences in post-exercise MVITs between the conditions (P = 0.242). In Study 1, post-exercise MVITs were negatively correlated with the total torque-time integral (rrm = -0.53; P = 0.034). CONCLUSIONS:Pre-exercise caffeine supplementation induces greater exercise-induced torque reduction during the 48-h post-exercise period after eccentric exercise, potentially suggesting greater EIMD. Additionally, increased eccentric load in accordance with caffeine's ergogenic effect may contribute to this greater post-exercise torque-reduction. Therefore, the potential impact on post-exercise muscle function should be considered when caffeine is used as a preworkout supplement for resistance exercise.
BACKGROUND:Musculoskeletal injuries (MSKIs) pose a major threat to military readiness, affecting nearly 40% of personnel annually, driving over 5 million medical visits and 24 million limited duty days. Validated methods for identifying and preventing injuries are a priority for the Department of Defense. PURPOSE:To externally validate a previously developed prediction model for identifying MSKI risk in a U.S. Army airborne infantry brigade. STUDY DESIGN:Prospective cohort; model validation study. METHODS:U.S. Army paratroopers newly assigned to the 173rd Airborne Brigade (Nov 2022-Aug 2023) underwent baseline screening with a published risk prediction algorithm. The primary outcome was a duty-limiting MSKI within one year, identified through the Army's e-Profile database from the Medical Operations Data System. Model performance was assessed for discrimination, calibration, calibration-in-the-large, overall fit, and decision curve analysis, with internal validation using 2,000 bootstrap interactions. Performance was compared with the original model. RESULTS:308 paratroopers were prospectively followed for one year (93,636 military exposure days), during which 30.7% sustained a duty-limiting musculoskeletal injury. The model demonstrated poor discrimination (AUC 0.59, 95% CI 0.52-0.66) and only marginal net benefit over a treat-all strategy. CONCLUSIONS:The model failed to discriminate injury risk (AUC 0.59) and did not provide reliable calibration or meaningful net benefit. This model does not justify implementation for injury risk screening in this specific setting.
BACKGROUND:Hip and pelvic bone stress injuries (BSIs) represent a small but clinically significant subset of overuse injuries sustained during U.S. Army Basic Combat Training (BCT). However, the long-term military service and healthcare implications remain unclear. This study examined the impact of hip and pelvic BSIs sustained during BCT on subsequent military career outcomes and musculoskeletal healthcare utilization. METHODS:In this case-control study, BCT graduates from fiscal years 2015 to 2017 were analyzed. Cases included 895 BCT graduates with MRI-confirmed hip or pelvic BSI, representing 63.6% of all BSI-diagnosed trainees; controls (n=2,685) were BCT graduates without BSI, matched 3:1 by age and sex. Adjusted logistic regression models evaluated differences in Advanced Individual Training (AIT) graduation, service retention, and satisfactory completion of obligated service. Time-to-discharge was analyzed using Cox proportional hazards models, and annual musculoskeletal healthcare encounters were compared using negative binomial regression. RESULTS:Compared with controls, trainees with MRI-confirmed hip and pelvic BSIs had significantly worse career and healthcare outcomes. BSI cases had significantly lower odds of graduating from AIT (OR = 0.27, 95% CI: 0.18-0.41) and lower odds of satisfactory completion of obligated service (OR = 0.62, 95% CI: 0.48-0.79) compared to controls. BSI cases had a higher risk of early discharge (HR = 1.44, 95% CI: 1.30-1.60). Female cases demonstrated higher attrition and lower graduation rates than males. Musculoskeletal healthcare utilization was 2.6 times higher among BSI cases during the first post-BCT year (RR = 2.61, 95% CI: 2.31-2.96) and remained elevated through year three. CONCLUSIONS:Trainees who sustain hip or pelvic BSIs during BCT experience lasting negative impacts on military retention and healthcare utilization, despite successfully graduating from BCT. These injuries impose a disproportionate long-term burden, particularly among female trainees. Targeted prevention and comprehensive rehabilitation strategies are essential to mitigate their career and readiness impacts.
PURPOSE:To examine the effects of exercise timing (morning [AX] vs evening [PX]) on functional capacity, psychological outcomes, and sleep-related measures in cancer patients undergoing treatment. METHODS:Forty-four cancer patients undergoing treatment participated in a supervised exercise intervention at the University of Northern Colorado Cancer Rehabilitation Institute (UNCCRI). Participants self-selected exercise timing as AX (0700-0900) or PX (1600-1800) and completed a range of pre- and post-intervention physical and psychological assessments. A subset of participants (n=24) completed objective sleep and recovery monitoring using a wearable tracker. RESULTS:Both AX and PX groups demonstrated significant improvements in functional capacity, with no significant differences between groups for these variables (p > 0.05). In contrast, exercise timing was associated with significant differences in psychological and autonomic outcomes. The AX group demonstrated greater reductions in Beck Depression scores (-4.86 ± 5.72 vs -1.02 ± 4.48; p < 0.05) and greater improvements in PSQI scores (-3.76 ± 3.39 vs 0.08 ± 1.83; p < 0.001) compared to the PX group. The AX group exhibited a substantially greater increase in heart rate variability (8.01 ± 6.31 ms) compared to a decrease in the PX group (-4.49 ± 6.79 ms; p < 0.001), representing a marked divergence in autonomic adaptation between groups. These differences were supported by moderate-to-large to very large effect sizes, indicating clinically relevant improvements in autonomic and psychological outcomes. No other objective sleep variables differed significantly between groups. CONCLUSIONS:A 12-week supervised exercise intervention improved functional capacity in cancer patients undergoing treatment, independent of exercise timing. However, morning exercise was associated with greater improvements in autonomic function, sleep quality, and depressive symptoms compared to afternoon/evening exercise.
PURPOSE:The relationship between exercise and brain function has been studied extensively; however, whether different exercise modalities promote hippocampal neurogenesis and cognitive function through shared or distinct biological pathways remains unclear. This study examined the effects of endurance training (ET), resistance training (RT), and high-intensity interval training (HIIT) on hippocampal neurogenesis, spatial memory, and neurotrophic factors. METHODS:Forty 3-month-old male C57BL/6J mice were randomized to control (SED), ET, RT, or HIIT groups. Following the training intervention, adult hippocampal neurogenesis was assessed in the dentate gyrus using BrdU⁺/NeuN⁺ immunolabeling. Hippocampal measures of neurotrophic factors, including brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and fibronectin type III domain-containing protein (FNDC5), were quantified. Spatial memory was evaluated using the Barnes maze. RESULTS:All exercise modalities increased the number of BrdU⁺/NeuN⁺ cells compared with sedentary controls (RT, p<0.001; ET, p=0.001; HIIT, p=0.016). Each modality produced a distinct molecular profile. RT elicited the greatest increases in hippocampal BDNF compared to all groups (RT vs. ET, p=0.007; RT vs. HIIT, p<0.001; RT vs. SED, p<0.001) and increased IGF-1 levels (RT vs. SED, p=0.014). ET increased hippocampal FDNC5 (ET vs. SED, p=0.033), whereas HIIT did not alter measured neurotrophic or myokine levels. Only RT and ET improved spatial learning. CONCLUSIONS:Although all exercise modalities increased hippocampal neurogenesis, only those associated with elevations in neurotrophic factors demonstrated improvements in spatial learning. These findings suggest that different exercise modalities may promote hippocampal plasticity through distinct biological profiles and that increases in neurogenesis alone may not be sufficient to enhance cognitive function.
PURPOSE:To compare changes in running biomechanics between two gait modifications: cues to run softly and quietly (SOF) and shifting to a forefoot strike pattern (FFS). METHODS:Thirty-eight individuals completed testing, including running with habitual gait (HAB) and the two gait modifications, while biomechanical data were collected. Variables of interest included joint angles and moments, knee stiffness, and ground reaction forces. Repeated measures analysis of variance was used to compare gait conditions. RESULTS:The SOF condition showed higher peak knee flexion angles and excursion, foot strike angles (vs. HAB and FFS), and higher peak and initial contact ankle dorsiflexion angles, peak eversion angles, and lower initial contact ankle inversion angles (vs. FFS). The FFS condition resulted in a more plantarflexed and inverted ankle at initial contact, as well as a more plantarflexed foot. The SOF condition resulted in reduced peaks and loading rates for vertical and posterior forces, however FFS led to reduced vertical loading rates compared to HAB and SOF. For joint moments, the SOF condition showed increased hip flexion and extension moments and reduced knee stiffness (vs. HAB and FFS), and reduced ankle plantarflexion moments (vs. FFS). The FFS condition also showed increased knee flexion and ankle plantarflexion moments compared to HAB. CONCLUSIONS:The SOF modification was shown to be a viable alternative to FFS for reducing several key aspects of biomechanical loading during running, including sagittal knee and ankle moments and knee stiffness, as well as peaks and loading rates for vertical and posterior ground reaction forces. However, the increases in hip joint moments should lead to some caution and warrant further investigation.
PURPOSE:Although perceptual scales are widely used to prescribe endurance training, whether aerobic training status influences perceptual responses to heavy-intensity exercise remains unclear. Thus, this study investigated the effects of aerobic training status on perceptual responses during cycling performed at the maximal metabolic steady state (MMSS). METHODS:Thirty-two participants (untrained, n = 18; trained, n =14) performed:1) step-ramp-step to determine maximal oxygen uptake (V̇O2max) and, 2) MMSS estimated intensity, followed by at least two 30 min constant workload rides to confirm the MMSS. The MMSS was defined as the highest exercise intensity at which oxygen uptake and blood lactate concentration were stable between the 15 th and 30 th min of exercise (change <120 mL·min -1 and <1 mmol·L -1, respectively). During the MMSS ride, rating of perceived exertion (RPE, 6-20), fatigue, leg pain, and dyspnea scales (0-10) were recorded at baseline and every 5 min until the end of exercise. RESULTS:V̇O2max (36.2 ± 6.6 mL·kg -1·min -1) and MMSS intensity (134 ± 40 W) were lower in untrained than trained group (V̇O2max: 54.0 ± 3.4 mL·kg -1·min -1; MMSS intensity: 209 ± 46 W) (p<0.001). Group×time interactions were observed for RPE (p≤0.001), fatigue (p=0.003), leg pain (p=0.009), and dyspnea (p=0.0018).Compared with the trained, the untrained group reported higher fatigue from 15 to 30 min (Δ= 2 a.u vs 1 a.u) and higher RPE (Δ= 2 a.u vs 1 a.u), leg pain (Δ= 2 a.u vs 1 a.u), and dyspnea from 20 to 30 min (Δ= 2 a.u vs 1 a.u) (post hoc p ≤0.04). CONCLUSIONS:Training status modulates the time course of perceptual drift at MMSS, with higher perceptual responses in untrained than trained individuals. Between-group differences emerged around 15 min, highlighting the importance of considering exercise duration when using perceptual scales to guide exercise at MMSS.
PURPOSE:This study aimed to develop and validate Elastic Net-based predictive models using simple anthropometric measurements to estimate dual-energy X-ray absorptiometry (DXA)-derived body composition variables in older women. METHODS:Body mass, skinfolds, circumferences, and DXA measures of total and regional fat mass (FM) and lean soft tissue (LST) were obtained from 523 older women. Elastic Net regression developed models for total body, upper- and lower-limb FM and LST, and android and gynoid FM. The sample was split into training, validation, and independent testing sets. RESULTS:Elastic Net models demonstrated high predictive accuracy for DXA-derived body composition. Coefficients of determination were strong for total FM and LST (R² ≥ 0.884), and good for regional compartments (R²≥ 0.711). Root mean square errors were low across outcomes (0.272-1.858 kg). Bland-Altman analyses showed minimal mean bias for most variables, except for lower-limb FM and android FM, which presented small but significant biases (≤ 2.78 %). Proportional bias was identified in some models, although the explained variance remained low (≤22%). Limits of agreement were narrow for total body estimates (≤11.73%), while wider limits were observed for segmental measures. CONCLUSIONS:Elastic Net-based models provide accurate estimates of total body composition and acceptable estimates of regional compartments, although regional predictions showed greater individual variability than total body estimates. However, these prediction equations should be interpreted as internally validated models intended primarily for screening and research applications.
OBJECTIVES:Assess differences in lower limb strength between adolescents with and without patellofemoral pain (PFP) and explore the association between strength and pain in adolescents with PFP. DESIGN:Cross-sectional. METHODS:One hundred and two male and female (n=24) adolescents aged 12-19 (mean=17 years ± 2) participated in this cross-sectional study (n=51 with PFP and n=51 age- and sex-matched controls). Strength was measured as peak isometric torque (Nm) using an isokinetic dynamometer during knee extension/flexion, and ankle plantar flexion. The worst pain in the previous week was rated on an 11-point numerical rating scale (0=no pain, 10=worst pain imaginable). Differences in strength between participants with and without PFP, as well as associations between strength measures and pain in adolescents with PFP, were investigated using separate linear regression models, unadjusted and adjusted for age, sex, and body weight. RESULTS:Adjusted mean (95% confidence interval [CI]) knee extension strength was 18.2 (3.6-32.8)Nm less in adolescents with PFP than in controls. For every one-point increase in pain, there was a mean (95% CI) adjusted reduction of 8.0 (15.4-0.6)Nm and an unadjusted reduction of 12.6 (23.5-1.7)Nm of knee extension torque in the PFP group. There were no between-group differences or associations between strength and pain for the other strength measures. CONCLUSIONS:Adolescents with PFP may have lower knee extension strength than their pain-free counterparts. Higher pain may be associated with lower knee extension strength in adolescents with PFP. Future research may investigate whether increases in knee extension strength in adolescent PFP mediate improvements in pain.
INTRODUCTION:Caffeine is well recognized to acutely enhance repeated sprint performance during intermittent exercise involving brief, repeated efforts. However, it remains unclear whether a single pre-exercise dose improves repeated sprint performance, and whether it alters noradrenergic, cardiorespiratory, and perceptual responses over several hours. METHODS:12 healthy young adults (4 females) completed two randomized, double-blind trials ingesting caffeine (5.5 mg·kg⁻¹) or placebo. Approximately 60 min after ingestion, participants performed three repeated sprint sets over a 3.5 h protocol. Each set consisted of 5 min of moderate-intensity cycling followed by 6 × 5 s sprints. Plasma samples were collected for caffeine and noradrenaline concentration analysis. Ratings of perceived exertion (RPE), leg muscle pain, respiratory variables, and heart rate were recorded. Middle cerebral artery mean blood velocity (MCAVmean), an index of cerebral blood flow, was measured using transcranial Doppler, and carotid artery blood flow was assessed using ultrasound. RESULTS:Caffeine increased mean sprint power across repeated sprint sets compared with placebo (P < 0.05), with modest but consistent effects sustained up to 3.5 h post-ingestion (0.5-2.4%). Peak power was also enhanced in the second and third sets, with increases of up to 3.7% (P < 0.05). These effects were accompanied by higher plasma noradrenaline concentrations (P < 0.05) and lower RPE and leg muscle pain (P < 0.05). Caffeine also reduced partial pressure of end-tidal CO2 and MCAVmean, and increased heart rate (P < 0.05). CONCLUSIONS:A single pre-exercise dose of caffeine (5.5 mg·kg⁻¹) sustains ergogenic effects across multiple repeated sprint bouts over 3.5 h post-ingestion. These improvements were observed alongside increased noradrenergic activity, reduced perceptual strain, and concomitant cardiorespiratory responses.
PURPOSE:The world's fastest vertical kilometer course in Fully (Switzerland) is comprised of stairs at a very steep grade (~31°). The aim was to determine whether stair ascent, with and without poles, lowered physiological, mechanical, and neuromuscular demands compared with continuous uphill ramp locomotion at VK-relevant slopes. METHODS:Twenty-two endurance-trained participants completed randomized treadmill trials at a constant vertical speed (800 m·h-1) in three conditions: uphill ramp (R), stairs (S), and stairs with poles (SP), each performed at six slopes (18-38°). Metabolic power (MP), heart rate (HR), minute ventilation (V̇E), rating of perceived exertion (RPE), internal mechanical work, step frequency, and lower-limb electromyography were measured. RESULTS:At 18°, S elicited greater MP (6%), HR (4%), and V̇E (7%) compared to R (all P<0.001), with no difference in RPE. From 26° to 38°, S elicited less MP (6-10%), HR (5-10%), V̇E, and RPE relative to R (all P≤0.05). Across 26-38°, S involved less internal mechanical work (23-45%, P<0.001), lower step frequency (P<0.001), and reduced gastrocnemius lateralis activity (P<0.001) compared with R. Relative to S, SP reduced gastrocnemius lateralis and vastus lateralis activity (P<0.05) but did not change MP, HR, V̇E, or RPE (all p≥0.09). CONCLUSIONS:On very steep slopes, stairs improve uphill economy and reduce rate of perceived exertion, likely through reductions in internal mechanical work and plantar-flexor demand. These findings provide a mechanistic explanation for exceptional performances on VK courses featuring extended stair sections. Using poles on stairs altered the activation of the measured lower-limb muscles, particularly by reducing gastrocnemius lateralis activity, without clear physiological or perceptual benefit at the tested intensity.
Purpose: To examine the associations of physical activity (PA) and physical fitness with executive function among disabled children and adolescents, and explore potential differences across disability types and gender. Methods: Two hundred and forty-one participants (64.3% boys; mean age: 12.96 ± 3.29 years) with physical disabilities (PD, n = 112), intellectual disabilities (ID, n = 119), and hearing impairment (n = 10) were recruited from 19 special schools. PA was measured with wrist-worn accelerometers. Physical fitness, including body composition, muscular strength, muscular endurance, and flexibility, was assessed using the Brockport Physical Fitness Test. Executive function was evaluated through computer-based tasks that measured mean accuracy and reaction time. Results: Linear mixed models revealed that higher PA and better muscular fitness were positively associated with the accuracy of executive function tests. Both light PA (LPA, B = 0.03; 95% confidence intervals [CI]: 0.00, 0.06; d = 0.295) and moderate-to-vigorous PA (MVPA; B = 0.25; 95%CI: 0.14, 0.36; d = 0.611) showed significant associations with accuracy. Muscular fitness, including curl-ups ( B = 0.58; 95% CI: 0.16, 1.00; d = 0.285) and handgrip strength ( B = 0.74; 95% CI: 0.42, 1.07; d = 0.587), demonstrated positive associations with accuracy. Disability-specific analyses indicated that MVPA and handgrip strength were consistently associated with accuracy in both PD and ID groups, while PA was associated with reaction time only in the PD group. Gender-stratified analyses revealed that muscular fitness showed stronger associations with executive function in PD boys, whereas MVPA demonstrated stronger associations with accuracy in PD girls. Conclusions: Promoting PA and improving muscular fitness may enhance executive function in disabled children and adolescents, with patterns varying by disability type and gender. However, the cross-sectional design precludes causal inferences, and future longitudinal studies are needed to establish causality and explore potential mediating mechanisms.
PURPOSE:Greater moderate-to-vigorous physical activity (MVPA) and light physical activity (LPA), with lower sedentary behavior (SED) during pregnancy are associated with more favorable maternal-child health. There is limited research examining the co-occurrence of these behaviors and who may be at risk for less optimal activity patterns across pregnancy. This study identifies and examines predictors of distinct activity profiles across pregnancy. METHODS:The present study is a secondary analysis of the Pregnancy 24/7 prospective cohort study (n=470). Participants wore a thigh-mounted accelerometer for up to 7 full days in each trimester to measure waking minutes per day of SED, LPA, and MVPA. Latent profile analysis identified distinct longitudinal activity patterns across pregnancy. Stepwise multinomial logistic regression examined predictors of profile membership. RESULTS:Five latent profiles were identified: High Sedentary (22%), Mixed Sedentary (34%), Mixed Active (25%), and High LPA (7%), High MVPA (12%). Activity patterns were stable across trimesters but differed substantially between profiles. Living with one or more children under age 5 (Relative risk ratio [RRR]: 2.15-3.84) and standing or active occupations (RRR: 9.25-45.77) were associated with greater likelihood of belonging to Mixed Active or High LPA profiles. Pre-pregnancy body mass index ≥30 kg/m² was associated with lower likelihood of membership in all more active profiles, particularly High MVPA (RRR: 0.13), compared to High Sedentary. Multiparous individuals were more likely to belong to higher LPA profiles, whereas nulliparous individuals were more likely to exhibit higher MVPA. CONCLUSIONS:Distinct patterns of activity occur across pregnancy. Those without children under age 5, in sedentary occupations, and with pre-pregnancy BMI ≥30 kg/m 2 had less favorable patterns and may benefit from targeted physical activity interventions to promote maternal-child health.
