Skeletal muscle fiber type and TMS-induced muscle relaxation in unfatigued and fatigued knee-extensor muscles.

The force drop after transcranial magnetic stimulation (TMS) delivered to the motor cortex during voluntary muscle contractions could inform about muscle relaxation properties. Because of the physiological relation between skeletal muscle fiber-type distribution and size and muscle relaxation, TMS could be a noninvasive index of muscle relaxation in humans. By combining a noninvasive technique to record muscle relaxation in vivo (TMS) with the gold standard technique for muscle tissue sampling (muscle biopsy), we investigated the relation between TMS-induced muscle relaxation in unfatigued and fatigued states, and muscle fiber-type distribution and size. Sixteen participants (7F/9M) volunteered to participate. Maximal knee-extensor voluntary isometric contractions were performed with TMS before and after a 2-min sustained maximal voluntary isometric contraction. Vastus lateralis muscle tissue was obtained separately from the participants' dominant limb. Fiber type I distribution and relative cross-sectional area of fiber type I correlated with TMS-induced muscle relaxation at baseline (r = 0.67, adjusted P = 0.01; r = 0.74, adjusted P = 0.004, respectively) and normalized TMS-induced muscle relaxation as a percentage of baseline (r = 0.50, adjusted P = 0.049; r = 0.56, adjusted P = 0.031, respectively). The variance in the normalized peak relaxation rate at baseline (59.8%, P < 0.001) and in the fatigue resistance (23.0%, P = 0.035) were explained by the relative cross-sectional area of fiber type I to total fiber area. Fiber type I proportional area influences TMS-induced muscle relaxation, suggesting TMS as an alternative method to noninvasively inform about skeletal muscle relaxation properties.NEW & NOTEWORTHY Transcranial magnetic stimulation (TMS)-induced muscle relaxation reflects intrinsic muscle contractile properties by interrupting the drive from the central nervous system during voluntary muscle contractions. We showed that fiber type I proportional area influences the TMS-induced muscle relaxation, suggesting that TMS could be used for the noninvasive estimation of muscle relaxation in unfatigued and fatigued human muscles when the feasibility of more direct method to study relaxation properties (i.e., muscle biopsy) is restricted.

Downhill running increases markers of muscle damage and impairs the maximal voluntary force production as well as the late phase of the rate of voluntary force development.

PURPOSE: To examined the time-course of the early and late phase of the rate of voluntary force development (RVFD) and muscle damage markers after downhill running. METHODS: Ten recreational runners performed a 30-min downhill run at 10 km h-1 and -20% (-11.3°) on a motorized treadmill. At baseline and each day up to 4 days RVFD, knee extensors maximum voluntary isometric force (MVIC), serum creatine kinase (CK) concentration, quadriceps swelling, and soreness were assessed. The early (0-50 ms) and late (100-200 ms) phase of the RVFD, as well as the force developed at 50 and 200 ms, were also determined. RESULTS: MVIC showed moderate decrements (p < 0.05) and recovered after 4 days (p > 0.05). Force at 50 ms and the early phase were not impaired (p > 0.05). Conversely, force at 200 ms and the late phase showed moderate decrements (p < 0.05) and recovered after 3 and 4 days, respectively (p > 0.05). CK concentration, quadriceps swelling, and soreness increased (p < 0.05) were overall fully resolved after 4 days (p > 0.05). CONCLUSION: Downhill running affected the knee extensors RVFD late but not early phase. The RVFD late phase may be used as an additional marker of muscle damage in trail running.

Performance fatigability and recovery after dynamic multi-joint maximal exercise in elbow flexors versus knee extensors.

Elbow flexors (EFs) and knee extensors (KEs) have shown differences in performance fatigability and recovery of neuromuscular function after isometric and isotonic single-joint fatiguing contractions. However, dynamic multi-joint movements are more representative of real-world activities. The aim of the study was to assess central and peripheral mechanisms of fatigability after either arm-cranking or cycling. Ten physically active men performed maximal incremental arm-cranking and cycling until task failure. Maximal voluntary isometric contraction (MVIC) and electrically evoked forces of both EF and KE were assessed before (PRE) and 1 (POST) and 20 (POST20) min after exercise. At POST, MVIC decreased similarly to 76 ± 8% and 81 ± 7% (both P < 0.001) of PRE for EF and KE, respectively. MVIC force remained lower than PRE at POST20 for both EF and KE (85 ± 8% vs. 95 ± 3% of PRE, P ≤ 0.033), having recovered less in EF than in KE (P = 0.003). Electrically evoked forces decreased similarly from PRE to POST in EF and KE (all P > 0.05). At POST20, the ratio of low-to-high frequency doublets was lower in EF than in KE (75 ± 13% vs. 85 ± 10% of PRE; P ≤ 0.034). Dynamic maximal incremental exercise acutely induced similar magnitudes of MVIC and evoked force loss in EF and KE. However, at POST20, impaired MVIC recovery and lower ratio of low-to-high frequency doublets in EF than in KE suggest the recovery of neuromuscular function after dynamic maximal exercises is specific to and dependent on changes within the muscles investigated.

Downhill running affects the late but not the early phase of the rate of force development.

PURPOSE: This study aimed to evaluate the acute changes in the knee extensors maximum voluntary isometric contraction force (MVIC), rate of force development (RFD), and rate of EMG rise (RER) following a bout of downhill running. METHODS: MVIC and RFD at 0-50, 50-100, 100-200, and 0-200 ms were determined in thirteen men (22 ± 2 yr) before and after 30 min of downhill running (speed: 10 km h-1; slope: - 20%). Vastus lateralis maximum EMG (EMGmax) and RER at 0-30, 0-50, and 0-75 ms were also recorded. RESULTS: MVIC, RFD0-200, and EMGmax decreased by ~ 25% [Cohen's d = - 1.09 (95% confidence interval: - 1.88/- 0.24)], ~ 15% [d = - 0.50 (- 1.26/0.30)], and ~ 22% [d = - 0.37 (- 1.13/0.42)] (all P < 0.05), respectively. RFD100-200 was also reduced [- 25%; d = - 0.70 (- 1.47/0.11); P < 0.001]. No change was observed at 0-50 ms and 50-100 ms (P ≥ 0.05). RER values were similar at each time interval (all P > 0.05). CONCLUSION: Downhill running impairs the muscle capacity to produce maximum force and the overall ability to rapidly develop force. No change was observed for the early phase of the RFD and the absolute RER, suggesting no alterations in the neural mechanisms underlying RFD. RFD100-200 reduction suggests that impairments in the rapid force-generating capacity are located within the skeletal muscle, likely due to a reduction in muscle-tendon stiffness and/or impairments in the muscle contractile apparatus. These findings may help explain evidence of neuromuscular alterations in trail runners and following prolonged duration races wherein cumulative eccentric loading is high.

Internal Tibial Forces and Moments During Graded Running.

The stress experienced by the tibia has contributions from the forces and moments acting on the tibia. We sought to quantify the influence of running grade on internal tibial forces and moments. Seventeen participants ran at 3.33 m/s on an instrumented treadmill at 0 deg, ±5 deg, and ±10 deg while motion data were captured. Ankle joint contact force was estimated from an anthropometrically-scaled musculoskeletal model using inverse dynamics-based static optimization. Internal tibial forces and moments were quantified at the distal 1/3rd of the tibia, by ensuring static equilibrium with all applied forces and moments. Downhill running conditions resulted in lower peak internal axial force (range of mean differences: -9% to -16%, p < 0.001), lower peak internal anteroposterior force (-14% to -21%, p < 0.001), and lower peak internal mediolateral force (-14% to -15%, p < 0.001), compared to 0 deg and +5 deg. Furthermore, downhill conditions resulted in lower peak internal mediolateral moment (-11%to -21%, p < 0.001), lower peak internal anteroposterior moment (-13% to -14%, p < 0.001), and lower peak internal torsional moment (-9% to -21%, p < 0.001), compared to 0 deg, +5 deg, and +10 deg. The +10 deg condition resulted in lower peak internal axial force (-7% to -9%, p < 0.001) and lower peak internal mediolateral force (-9%, p = 0.004), compared to 0 deg and +5 deg. These findings suggest that downhill running may be associated with lower tibial stresses than either level or uphill running.

Use of transcranial magnetic stimulation to assess relaxation rates in unfatigued and fatigued knee-extensor muscles.

We examined whether transcranial magnetic stimulation (TMS) delivered to the motor cortex allows assessment of muscle relaxation rates in unfatigued and fatigued knee extensors (KE). We assessed the ability of this technique to measure time course of fatigue-induced changes in muscle relaxation rate and compared relaxation rate from resting twitches evoked by femoral nerve stimulation. Twelve healthy men performed maximal voluntary isometric contractions (MVC) twice before (PRE) and once at the end of a 2-min KE MVC and five more times within 8 min during recovery. Relative (intraclass correlation coefficient; ICC2,1) and absolute (repeatability coefficient) reliability and variability (coefficient of variation) were assessed. Time course of fatigue-induced changes in muscle relaxation rate was tested with generalized estimating equations. In unfatigued KE, peak relaxation rate coefficient of variation and repeatability coefficient were similar for both techniques. Mean (95% CI) ICC2,1 for peak relaxation rates were 0.933 (0.724-0.982) and 0.889 (0.603-0.968) for TMS and femoral nerve stimulation, respectively. TMS-induced normalized muscle relaxation rate was - 11.5 ± 2.5 s-1 at PRE, decreased to - 6.9 ± 1.2 s-1 (- 37 ± 17%, P < 0.001), and recovered by 2 min post-exercise. Normalized peak relaxation rate for resting twitch did not show a fatigue-induced change. During fatiguing KE exercise, the change in muscle relaxation rate as determined by the two techniques was different. TMS provides reliable values of muscle relaxation rates. Furthermore, it is sufficiently sensitive and more appropriate than the resting twitch evoked by femoral nerve stimulation to reveal fatigue-induced changes in KE.

Spinal contribution to neuromuscular recovery differs between elbow-flexor and knee-extensor muscles after a maximal sustained fatiguing task.

Data from studies of elbow-flexor (EF) or knee-extensor (KE) muscles suggest that a fatigue-related decrease in motoneuron excitability only occurs in EF. It is unknown how motoneuron excitability changes after sustained fatiguing maximal voluntary isometric contractions (MVICs) in EF and KE in the same participants. In two sessions, eight healthy men performed a 2-min MVIC of EF or KE to induce fatigue with brief MVICs before and six times after the 2-min MVIC. Electromyographic responses elicited by corticospinal tract stimulation at the transmastoid [cervicomedullary motor-evoked potential (CMEP)] or thoracic [thoracic motor-evoked potential (TMEP)] level were recorded from EF and KE, respectively. To account for muscle excitability, CMEPs and TMEPs were normalized to maximal M-wave (Mmax) elicited by peripheral nerve stimulation during each brief MVIC. Immediately after the 2-min MVIC, biceps brachii and brachioradialis CMEP/Mmax were 88% (SD 11%) (P = 0.026) and 87% (SD 12%) (P = 0.029) of pre-MVIC (PRE) values, respectively, and remained lower than PRE after 5 s of recovery [91% (SD 8%), P = 0.036 and 87% (SD 13%), P = 0.046, respectively]. No subsequent time points differed from PRE (all P ≥ 0.253). TMEP/Mmax for rectus femoris and vastus lateralis were not different from PRE at any time during the recovery period (all P > 0.050). A different recovery pattern in motoneuron excitability occurred in EF as it recovered by 60 s whereas KE motoneurons were unaffected by the fatiguing task. The present findings may contribute to better understand muscle-specific neurophysiological differences in spinal excitability.NEW & NOTEWORTHY By comparing the changes in motoneuron excitability in elbow-flexor and knee-extensor muscles after sustained fatiguing maximal voluntary contractions, this study shows that motoneuron recovery behavior depends on the muscle performing the exercise. A different recovery pattern in motoneuron excitability occurs in elbow flexors as it recovered by 60 s whereas knee extensors were unaffected by fatigue. This finding can help to increase understanding of the effect of a fatigue and subsequent recovery on neural processes.

Biomechanics of graded running: Part I - Stride parameters, external forces, muscle activations.

Biomechanical alterations with graded running have only been partially quantified, and the potential interactions with running speed remain unclear. We measured spatiotemporal parameters, ground reaction forces, and leg muscle activations (EMG) in nineteen adults (10F/9M) running on an instrumented treadmills at 2.50, 3.33, and 4.17 m·s-1 and 0, ±5°, and ±10°. Step frequency illustrated a significant speed × grade interaction (P < .001) and was highest (+3%) at the steepest grade (+10°) and fastest speed (4.17 m·s-1 ) when compared to level running (LR) at the same speed. Significant interaction was also observed for ground reaction forces (all P ≤ .047). Peak ground reaction forces in the normal direction increased with running speed during downhill running (DR) only (+9% at -10° and 4.17 m·s-1 ). Impulse in the normal direction decreased at fastest speed and steepest DR (-9%) and uphill running (UR) (-17%) grades. Average normal loading rate increased and decreased at fastest speed and steepest DR (+52%) and UR (-28%) grades, respectively. Negative parallel impulse increased and decreased at fastest speed and steepest DR (+166%) and UR (-90%), respectively. Positive parallel impulse decreased and increased at fastest speed and steepest DR (-75%) and UR (+111%), respectively. EMG showed comparable u-shaped curves across the grades investigated, although only a change in vastus lateralis and tibilias anterior activity was detectable at the steepest grades and fastest speed. Overall, running grade and speed significantly influences spatiotemporal parameters, ground reaction forces, and muscle activations.

Biomechanics of graded running: Part II-Joint kinematics and kinetics.

Compared to level running (LR), different strategies might be implemented by runners to cope with specific challenges of graded running at different speeds. The changes in joint kinetics and kinematics associated with graded running have been investigated, but their interactions with speed are unknown. Nineteen participants ran on an instrumented treadmill at five grades (0°, ±5° and ± 10°) and three speeds (2.50, 3.33 and 4.17 m/s), while 3D motion and forces were recorded. Three speed × five-grade repeated-measures ANOVA was used to analyze kinetic and kinematic variables. A speed × grade interaction was observed for hip range of motion (ROM). Downhill running (DR) at fastest speed did not reduce ROM at the hip, compared to LR. Compared to LR, it was observed that the hip joint was responsible for a greater contribution of energy generation while running at the fastest speed at +10°. Speed × grade interactions were also observed for the energy absorption, peak moment, and peak power at the knee. Contrary to LR, running faster during UR did not require higher peak power at the knee. Finally, DR at the fastest speed did not increase peak negative power at the knee compared to LR. This study demonstrates that ankle, knee, and hip joint kinetics depend on speed and grade of running, while the effect of grade on joint kinematics was not substantially modulated by speed.

Defining Off-road Running: A Position Statement from the Ultra Sports Science Foundation.

Off-road running continues to grow in popularity, with differing event categories existing, and terminologies are often used interchangeably and without precision. Trail running, mountain running, skyrunning, fell running, orienteering, obstacle course racing and cross-country running all take place predominantly in off-road terrain. Ultramarathon running refers to any running event over marathon distance conducted in any terrain and surface. Although some overlap may exist between these running events, mainly through the common denominator of off-road terrain, distinct features need to be recognised. As scientific interest in these activities grows, it becomes important to clarify these terms and develop a universal language for discussing these events. Similarly, off-road running athletes are generally not properly defined within the scientific literature, which makes intra- and inter-study comparisons difficult. The current position statement of the Ultra Sports Science Foundation highlights the different off-road running events and recommends clear reference to distance, surface, elevation change and altitude, type of event (continuous vs. staged), type of support, name and year of the event, governing body, and guidance on terminology. We further recommend to describe off-road running athletes by basic data, physiological determinants, training and competition characteristics in the scientific literature in order to facilitate and guide further research and practice.

Do aerobic characteristics explain isometric exercise-induced neuromuscular fatigue and recovery in upper and lower limbs?

This study investigated the relationships between aerobic characteristics and (i) neuromuscular fatigue induced by 2-min sustained isometric maximal voluntary contractions (MVC) and (ii) subsequent recovery, in the upper and lower limbs. In a pseudo-randomized order, eleven healthy males completed four sessions on different days: maximal incremental cycling test (100 W + 40 W every 2 min); maximal arm-cranking test (50 W + 20 W every 2 min); and 2-min sustained isometric MVCs of the knee extensors (KE) and elbow flexors (EF). Neuromuscular assessment was performed with transcranial magnetic and peripheral nerve stimulation to evaluate central and peripheral neuromuscular factors of fatigue and the subsequent recovery. Peak oxygen uptake, gas exchange threshold and the corresponding power outputs were correlated with recovery of voluntary force after the 2-min KE MVC. Regression analysis showed that power output at the gas exchange threshold alone explained 72% of the variability in ∆recovery of KE voluntary force. No relationships with fatigue or recovery in EF were observed. These results suggest that participants with greater aerobic capacities experience the same amount of fatigue and faster recovery of voluntary force in KE but not EF. The potential reasons behind the relationship in KE but not EF are discussed.

Changes in Muscle Architecture of Vastus Lateralis Muscle After an Alpine Snowboarding Race.

Vernillo, G, Pisoni, C, Sconfienza, LM, Thiébat, G, and Longo, S. Changes in muscle architecture of vastus lateralis muscle after an alpine snowboarding race. J Strength Cond Res 31(1): 254-259, 2017-This study aimed to assess acute changes of vastus lateralis (VL) muscle architecture after an alpine snowboarding simulated race and to compare architecture characteristics between the front and rear legs on elite alpine snowboarders. Using ultrasonography, VL muscle thickness (MT), pennation angles (θ), and fascicle lengths (Lf) were assessed in 8 elite alpine snowboarders (25.6 ± 4.4 years; stature: 178.4 ± 9.8 cm; body mass: 78.1 ± 12.1 kg) before and directly after an alpine snowboarding simulated race under competition rules. Muscle thickness, θ, and Lf showed no meaningful changes (P > 0.05, differences reported as trivial) after the race for both legs. The rear leg tended to have a 14.0% lower θ (P = 0.04, differences rated as moderate) and a 13.6% higher Lf (P = 0.04, differences rated as moderate) compared with the front leg. Changes in muscle architecture are not observable immediately after an alpine snowboarding simulated race. The ∼14.0% difference in muscle architecture between the front and the rear leg suggests the presence of a morphological asymmetry in elite alpine snowboarders with direct implications for injury prevention and training prescription.

Fatigue associated with prolonged graded running.

Scientific experiments on running mainly consider level running. However, the magnitude and etiology of fatigue depend on the exercise under consideration, particularly the predominant type of contraction, which differs between level, uphill, and downhill running. The purpose of this review is to comprehensively summarize the neurophysiological and biomechanical changes due to fatigue in graded running. When comparing prolonged hilly running (i.e., a combination of uphill and downhill running) to level running, it is found that (1) the general shape of the neuromuscular fatigue-exercise duration curve as well as the etiology of fatigue in knee extensor and plantar flexor muscles are similar and (2) the biomechanical consequences are also relatively comparable, suggesting that duration rather than elevation changes affects neuromuscular function and running patterns. However, 'pure' uphill or downhill running has several fatigue-related intrinsic features compared with the level running. Downhill running induces severe lower limb tissue damage, indirectly evidenced by massive increases in plasma creatine kinase/myoglobin concentration or inflammatory markers. In addition, low-frequency fatigue (i.e., excitation-contraction coupling failure) is systematically observed after downhill running, although it has also been found in high-intensity uphill running for different reasons. Indeed, low-frequency fatigue in downhill running is attributed to mechanical stress at the interface sarcoplasmic reticulum/T-tubule, while the inorganic phosphate accumulation probably plays a central role in intense uphill running. Other fatigue-related specificities of graded running such as strategies to minimize the deleterious effects of downhill running on muscle function, the difference of energy cost versus heat storage or muscle activity changes in downhill, level, and uphill running are also discussed.

Strength Asymmetry Between Front and Rear Leg in Elite Snowboard Athletes.

OBJECTIVE: To examine possible bilateral strength asymmetries between the front (FL) and the rear leg (RL) in elite snowboard athletes due to the imposed asymmetrical position on the board. DESIGN: Observational study. SETTING: Department of Biomedical Sciences for Health, University of Milan. PARTICIPANTS: Thirty-three elite male snowboarders: 12 alpine athletes (SBalp), 11 snowboardcross athletes (SBx), and 10 freestyle athletes (SBfs). INTERVENTION: Open and closed kinetic chain exercises. MAIN OUTCOME MEASURES: Maximal isometric voluntary contraction (MVC) and vertical jump force (VJFT). RESULTS: Only SBalp athletes presented MVC and VJFT values in RL 9.9% and 11.3% greater than the corresponding value in FL (P < 0.001), respectively. No significant differences were observed in SBx and SBfs. CONCLUSIONS: A muscle strength asymmetry between FL and RL was detected only in elite SBalp. This asymmetry is lower than the ±15% cutoff interval used to define clinically relevant bilateral strength asymmetry and is likely to be explained by technical aspects. Indeed, only SBalp athletes naturally distributed the center of mass, and thus, the weight toward RL to have a good board control. This feature likely reflects a greater adaptation of the muscle characteristics.

Postexercise autonomic function after repeated-sprints training.

PURPOSE: We examined the effects of an 8-week repeated-sprint (RS) training protocol on postexercise parasympathetic reactivation (PNSr) in healthy adults. METHODS: Eighteen male adults (24.3 ± 3.7 years) were assigned to either of two groups. One group (n = 9) performed RS training (EXP, 3 times week(-1), 18 maximal all-out 15-m sprints interspersed with 17 s of passive recovery); the other served as the control group (CON, n = 9). Performance before, during, and after was assessed by measuring RS ability time (S dec) and total sprint time. The subjects were then seated for 10 min immediately after each trial and postexercise HR recovery (HRR), and vagal-related HR variability (HRV) indices were measured. RESULTS: All subjects demonstrated a decrease in S dec. However, only EXP showed a decrease in total sprint time (-10.5 % of baseline value). Using a qualitative statistical analysis method, we found a likely to almost certain positive effect of RS training on HR. The mean of each HRR and HRV index indicated a greater change in PNSr in EXP than in CON (e.g. with a 78/22/1 % chance to demonstrate a positive/trivial/negative effect on HRR60s after RS training; 74/21/5 % on LN rMSSD5-10min). Large correlations were noted between the changes in S dec [r = 0.59, 90 % CI (0.43)], total sprint time [r = -0.61 (0.42)] and HRR60s. CONCLUSION: RS training seems to be an effective method to improve postexercise PNSr in healthy adults. Also, HRR60s appears to be a method for evaluating positive adaption to RS training.

Energy cost and kinematics of level, uphill and downhill running: fatigue-induced changes after a mountain ultramarathon.

This study aimed to determine whether the fatigue induced by a mountain ultramarathon (MUM) led to changes in energy cost and kinematic during level and graded running. Pre- and post-race, 14 ultratrail runners ran on a level, uphill (5%) and downhill (5%) treadmill at 10 km · h(-1). Kinematic data were acquired using a photocell system. Post-race, the downhill energy cost increased by 13.1% (P < 0.001). No change was noted in level and uphill running. Duty factor and stride frequency were increased, whereas swing time, cycle time and stride length were decreased in all conditions (P < 0.05). Contact time was increased and the rate of force generation was decreased only in the uphill and downhill conditions (P < 0.05). Positive correlations were observed between performance time and the pre- to post-changes in the energy cost of level (r = 0.52, P = 0.04) and uphill running (r = 0.50, P = 0.04). MUM-induced fatigue resulted in physiological and spatiotemporal changes, though the response to fatigue varied considerably between running conditions. These changes resulted in a significant increment only in the downhill energy cost. Incorporating downhill locomotion in the training programmes of ultratrailers may help to improve performance-related physiological and biomechanical parameters.

Influence of the world's most challenging mountain ultra-marathon on energy cost and running mechanics.

PURPOSE: To examine the effects of the world's most challenging mountain ultra-marathon (Tor des Géants(®) 2012) on the energy cost of three types of locomotion (cycling, level and uphill running) and running kinematics. METHODS: Before (pre-) and immediately after (post-) the competition, a group of ten male experienced ultra-marathon runners performed in random order three submaximal 4-min exercise trials: cycling at a power of 1.5 W kg(-1) body mass; level running at 9 km h(-1) and uphill running at 6 km h(-1) at an inclination of +15 % on a motorized treadmill. Two video cameras recorded running mechanics at different sampling rates. RESULTS: Between pre- and post-, the uphill-running energy cost decreased by 13.8 % (P = 0.004); no change was noted in the energy cost of level running or cycling (NS). There was an increase in contact time (+10.3 %, P = 0.019) and duty factor (+8.1 %, P = 0.001) and a decrease in swing time (-6.4 %, P = 0.008) in the uphill-running condition. CONCLUSION: After this extreme mountain ultra-marathon, the subjects modified only their uphill-running patterns for a more economical step mechanics.

Evaluation of the SenseWear Mini Armband to assess energy expenditure during pole walking.

The current study aimed to show the validity of a portable motion sensor, the SenseWear Armband (SWA), for the estimation of energy expenditure during pole walking. Twenty healthy adults (mean ± SD: age 30.1 ± 7.2 year, body mass 66.1 ± 10.6 kg, height 172.4 ± 8.0 cm, BMI 22.1 ± 2.4 kg · m(-2)) wore the armband during randomized pole walking activities at a constant speed (1.25 m · s(-1)) and at seven grades (0%, ± 5%, ± 15% and ± 25%). Estimates of total energy expenditure from the armband were compared with values derived from indirect calorimetry methodology (IC) using a 2-way mixed model ANOVA (Device × Slope), correlation analyses and Bland-Altman plots. Results revealed significant main effects for device, and slope (p < .025) as well as a significant interaction (p < .001). Significant differences between IC and SWA were observed for all conditions (p < .05). SWA generally underestimate the EE values during uphill PW by 0.04 kcal · kg(-1) · min(-1) (p < .05). Whereas, a significant overestimation has been detected during flat and downhill PW by 0.01 and 0.03 kcal · kg(-1) · min(-1) (p < .05), respectively. The Bland-Altman plots revealed bias of the armband compared with the indirect calorimetry at any condition examined. The present data suggest that the armband is not accurate to correctly detect and estimate the energy expenditure during pole walking activities. Therefore, the observed over- and under-estimations warrants more work to improve the ability of SWA to accurately measure EE for these activities.

Sex differences in neuromuscular and biological determinants of isometric maximal force.

AIM: Force expression is characterized by an interplay of biological and molecular determinants that are expected to differentiate males and females in terms of maximal performance. These include muscle characteristics (muscle size, fiber type, contractility), neuromuscular regulation (central and peripheral factors of force expression), and individual genetic factors (miRNAs and gene/protein expression). This research aims to comprehensively assess these physiological variables and their role as determinants of maximal force difference between sexes. METHODS: Experimental evaluations include neuromuscular components of isometric contraction, intrinsic muscle characteristics (proteins and fiber type), and some biomarkers associated with muscle function (circulating miRNAs and gut microbiome) in 12 young and healthy males and 12 females. RESULTS: Male strength superiority appears to stem primarily from muscle size while muscle fiber-type distribution plays a crucial role in contractile properties. Moderate-to-strong pooled correlations between these muscle parameters were established with specific circulating miRNAs, as well as muscle and plasma proteins. CONCLUSION: Muscle size is crucial in explaining the differences in maximal voluntary isometric force generation between males and females with similar fiber type distribution. Potential physiological mechanisms are seen from associations between maximal force, skeletal muscle contractile properties, and biological markers.