Voluntary Force Research Articles

Robot-assisted training with functional electrical stimulation enhances lower extremity function after spinal cord injury.

Functional electrical stimulation (FES) synchronized with robot-assisted lower extremity training is used in spinal cord injury (SCI) rehabilitation to promote residual function. Data of SCI inpatients who trained lower limb mobilization on a stationary robotic system were retrospectively analyzed. The primary outcome was the improvement of muscle strength from the first through to the last training session during FES-induced as well as voluntarily induced flexion and extension. The secondary outcome was the sum score of voluntary muscle function in the lower limbs before and after the training period. Data from 72 patients with SCI (AIS A-D) were analyzed. For extension, FES-assisted strength increased (p < 0.001) from 25.2 to 44.0N, voluntary force (p < 0.001) from 24.4 to 39.9N. For flexion, FES-assisted flexion (p < 0.006) increased from 14.1 to 19.0N, voluntary flexion (p < 0.005) from 12.6 to 17.1N. There was a significant correlation between the increase in FES-assisted force and voluntary flexion (r=0.730, p=0.001) as well as between the increase in FES-assisted force and voluntary extension (r=0.881, p < 0.001). The sum score in muscle test increased from 15 to 24 points. Robot-assisted training with FES seems to support the regeneration of residual functions after SCI. This is evidenced by an improvement in motor function and strength in the lower limbs.

Novel Procedure for Determining the Finger Force in Flexion Depending on the Finger Position

Abstract Introduction: The design and development of a novel dynamic hand orthosis that allows individual and progressive adaptation to the patient’s condition require knowledge about the maximum voluntary contraction forces of the fingers. The following work presents a test setup and procedure for determination of isometric finger contraction forces during flexion depending on various finger positions and finger tasks. Methods: The test setup places hand and fingers in certain positions (position 0: grasping of a plate; position 1-3: circular grasping of cylinders of three different diameters). The force measurement is carried out using pressure sensing: A capacitive force sensor is placed on each fingertip. To perform various finger tasks, the subjects are asked for isometric contraction of defined finger groups and single fingers against the boundary system. For proof of the concept, measurements are performed with six subjects and compared with reference values from the literature. Results: The separated finger force of each finger can be captured during the finger tasks in varying positions. Furthermore, the total finger force of all active fingers can be determined. It is shown that the total finger force during contraction of all fingers (IMRLtask; 78.4N ± 25.8N, d2) is higher than during contraction of the index finger (25.8N ± 3.4N, d2). Furthermore, the single finger force of the index finger is higher than the index finger activity in IMRL-task. The results also show a tendency for the finger contraction force to increase with increasing flexion. Further investigations may require improvements to the method. In this proof of concept, this potential is revealed and discussed. However, the functionality of the test setup and procedure can be demonstrated.

Perceived Muscle Soreness Does Not Modulate Corticospinal Excitability

Soreness due to exercise-induced muscle damage temporarily impairs motor performance. Transcranial magnetic stimulation (TMS) is often used to assess subtle changes in corticospinal excitability (CSE) and motor system input-output properties and demonstrates sensitivity to chronic pain. Nevertheless, the acute effects of muscle soreness on TMS-based measures of corticospinal excitability require further investigation. PURPOSE: To examine the relationship between perceived muscle soreness and CSE of postural and lower-extremity muscles. METHODS: 12 healthy adults (3 W, age: 27.2 ± 5.4 yr, ht: 175.6 ± 11.0 cm, wt: 72.6 ± 13.4 kg) completed three visits with maximal anaerobic lower extremity exercise. At the start of each visit, participants confirmed they abstained from any physical activity 24 hr prior, and rated their overall residual muscle soreness using a 100 mm visual analog scale. Visits were ranked based on muscle soreness with the highest and lowest soreness visits retained for analysis. To assess CSE, electromyographic motor-evoked potentials (MEPs) were recorded from the right rectus abdominis (RA) and vastus lateralis (VL). Active motor thresholds (AMT) were determined for each muscle during 15% of maximal voluntary isometric force using a biphasic stimulator and 96 mm curved double coil. To determine CSE, ten TMS pulses were applied to each M1 hotspot at 120% AMT with the resultant MEPs averaged based on peak-to-peak amplitude from 15-65 ms post-stimulus. Paired-samples t-test were used to assess mean differences in soreness, AMT, and MEP amplitudes. RESULTS: As expected, muscle soreness differed between visits (mean difference: 25.3 mm, t = 5.08, p < 0.01). Similar motor-thresholds were observed for the RA (mean difference: 0.3%, t = 0.26, p = 0.80) and VL (mean difference: 0.5%, t = 0.45, p = 0.66). MEP amplitudes were also similar for the RA (mean difference: 0.13 mV, t = 1.74, p = 0.12) and VL (mean difference: 0.01 mV, t = 0.30, p = 0.77). CONCLUSION: Day-to-day variation in CSE during lower extremity and axial contractions is not explained by differences in muscle soreness. Future work should examine CSE at multiple timepoints after acute exercise and use various submaximal intensities to further clarify whether CSE is responsive to muscle soreness.

Age-associated Decline In 20-sec Stepping Test Performance In Independent, Community-dwelling Older Women

PURPOSE: To determine if there is an age-related decline in ST performance in independent, community-dwelling women (age 66-89 yrs; n = 1163). METHODS: Subjects completed an eyes open, 20-sec ST and fitness testing. ST measures included head total movement distance (TMD), head greatest placement (MMD), knee total movement distance (KMD) and stepping rate (STEP) determined with a KINECTTM infrared depth sensor. Ratio of KMD/TMD is an index of upper-body sway relative to lower-body. Fitness was defined by self-selected walking speed (NW), fast-walking speed (FW), timed up and go (UPGO), chair stand five-times (CS), and maximum voluntary knee extension force (MVC). Subjects were divided into age groups 65-69 (n = 178), 70-74 (n = 293), 75-79 (n = 417), 80-84 (n = 251), and > 85 (n = 24) yrs and differences examined by ANOVA; significance p < 0.05. Associations between age and ST measures were evaluated using Pearson product moment correlation. RESULTS: Individuals between 75-79 and 85+ groups were shorter, while body mass declined across each group, leveling off at 80 yrs. % body fat was greater, but equal in 80-84 and 85+ groups. TMD was greatest in 80-84 group; all others were similar. TMD and KMD increased in 75-79 through 85+ group. MMD was not different among groups. KMD/TMD was similar and greater in 75-79 and 80-84 yrs, while, 85+ was greater than all groups. Sway per STEP (TMD/KMD/STEP) increased progressively across groups. There was a progressive reduction in fitness variables beginning with 75-79 group. ST variables, except MMD, were significantly correlated with age, but coefficients were low (r = -0.23-0.12, p < 0.05). CONCLUSIONS: Age-related decline in ST performance observed primarily as a progressive increase in sway (KMD/TMD, and KMD/TMD/STEP) indicates reduced balance in accordance with our previous findings. Progressive reduction in static/dynamic balance negatively affects physical function (e.g. decrements in walking speed, TUG etc.) as observed here. This supports our recent findings that ST differentiates physical disability, indicates risk of falling, and “need for assistance”. Supported by JSPS (Grant number: 20 K11656)

Motor inhibition and its contribution to recovery of dexterous hand use after stroke.

Recovery of dexterous hand use is critical for functional outcome after stroke. Grip force recordings can inform on maximal motor output and modulatory and inhibitory cerebral functions, but how these actually contribute to recovery of dexterous hand use is unclear. This cohort study used serially assessed measures of hand kinetics to test the hypothesis that behavioural measures of motor modulation and inhibition explain dexterity recovery beyond that explained by measures of motor output alone. We also investigated the structural and functional connectivity correlates of grip force control recovery.Eighty-nine adults (median age = 54 years, 26% females) with first-ever ischaemic or haemorrhagic stroke and persistent arm and hand paresis were assessed longitudinally, at 3 weeks, and at 3 and 6 months after stroke. Kinetic measures included: maximal grip force, accuracy of precision and power grip force control, and ability to release force abruptly. Dexterous hand use was assessed clinically with the Box and Block Test and motor impairment with the upper extremity Fugl-Meyer Assessment. Structural and functional MRI was used to assess weighted corticospinal tract lesion load, voxel-based lesion symptom mapping and interhemispheric resting-state functional connectivity.Fifty-three per cent of patients had severe initial motor impairment and a majority still had residual force control impairments at 6 months. Force release at 3 weeks explained 11% additional variance of Box and Block Test outcome at 6 months, above that explained by initial scores (67%). Other kinetic measures did not explain additional variance of recovery. The predictive value of force release remained significant when controlling for corticospinal tract lesion load and clinical measures. Corticospinal tract lesion load correlated with recovery in grip force control measures. Lesions involving the parietal operculum, insular cortex, putamen and fronto-striatal tracts were also related to poorer force modulation and release. Lesions to fronto-striatal tracts explained an additional 5% of variance in force release beyond the 43% explained by corticospinal injury alone. Interhemispheric functional connectivity did not relate to force control recovery.We conclude that not only voluntary force generation but also force release (reflecting motor inhibition) are important for recovery of dexterous hand use after stroke. Although corticospinal injury is a main determinant of recovery, lesions to integrative somatosensory areas and fronto-parietal white matter (involved in motor inhibition) explain additional variance in post-stroke force release recovery. Our findings indicate that post-stroke upper limb motor impairment profiling, which is essential for targeted treatment, should consider both voluntary grasp generation and inhibition.

Effect of leg dominance on ipsilateral and contralateral limb training adaptation in middle-aged women after unilateral sensorimotor and resistance exercise training

ABSTRACT The aim was to examine the directionality of global training effects in middle-aged women after unilateral training. Thirty-nine middle-aged female volunteers (59.4 ± 5.4 years) were randomly assigned to one of three groups: 1. Unilateral Dominant Lower Limb Training (UDLT); 2. Unilateral Non-Dominant Lower Limb Training (UNDLT) or 3. Control group. Outcome measures assessing isometric strength, static and dynamic balance were recorded at baseline, and 1 week after 12 weeks (post-test) of training or no-intervention. The net cross education adaptation changes of the contralateral quadriceps isometric maximum voluntary (MVC) force (F2,34 = 4.33; p = 0.022), Stork balance score (F2,34 = 4.26; p = 0.023) and the Star Excursion Balance test score (F2,34 = 11.80; p = 0.001) were asymmetrical in the UNDLT group and on average, exceeded the UDLT group. The results demonstrated asymmetrical cross education training adaptations with unilateral training of non-dominant leg (UNDLT) to contralateral homologous and heterologous muscles, with the exception of knee flexor MVC. The results of this study provide a novel exercise or rehabilitation strategy that can be employed when one of the limbs is affected.

Acute neuromuscular and hormonal responses to 20 versus 40% velocity loss in males and females before and after 8 weeks of velocity‐loss resistance training

New Findings What is the central question of this study? Do males and females differ in fatiguability during dynamic loadings, and what are the acute neuromuscular and hormonal responses to 20 versus 40% velocity‐loss resistance loadings? How does an 8‐week velocity‐loss resistance training period modify acute neuromuscular and hormonal responses in males and females? What is the main finding and its importance? Using resistance training methods that regulated the within‐set fatigue limit, males appeared to be more susceptible to fatigue than females before the training period. This between‐sex difference was diminished after training. The predominant mechanisms of fatigue from 20 and 40% velocity‐based resistance training appear to be within the musculature. Scientific examination of velocity‐based resistance training (VBRT) has increased recently, but how males and females respond to different VBRT protocols or how these acute responses are modified after a period of training is unknown. Habitually resistance‐trained males and females followed either a 20 or 40% velocity‐loss programme for 8 weeks. Acute squat loading tests (five sets, 70% one‐repetition maximum load, 3 min rest) were performed before and after the training period. Tests of maximum neuromuscular performance and blood sampling were conducted before, within 10 min of completion (POST) and 24 h after each acute loading test. Testing included countermovement jump, resting femoral nerve electrical stimulation and bilateral isometric leg press. Blood samples were analysed for whole‐blood lactate, serum testosterone, cortisol, growth hormone and creatine kinase concentrations. Countermovement jump height, maximum isometric bilateral leg‐press force and the force from a 10 Hz doublet decreased in all groups at POST after 20 and 40% velocity loss. Only males showed reduced force from the 100 Hz doublet and voluntary force over 100 ms at POST before training. The 40% velocity loss led to increased blood lactate and growth hormone responses before training in both males and females. After training, more systematic and equivalent responses in force over 100 ms, force from a 100 Hz doublet and blood lactate were observed regardless of sex/VBRT protocol. Overall, acute responses were greater from 40% VBRT, and males were more susceptible to acute loss in force production capacity before the training period. These VBRT protocol‐ and sex‐related differences were diminished after training.

Slouched and Erect Sitting Postures Affect Upper Limb Maximum Voluntary Force Levels and Fatiguability: A Randomized Experimental Study

OCCUPATIONAL APPLICATIONS Modifying the spinal curvature is an empirical approach to treating upper limb musculoskeletal disorders, often attributed to the balance between physical stress and individual functional capacities. We completed an experimental biomechanical study to quantify the effect of seated spinal posture on upper limb functional capacities. Isometric maximum muscle voluntary forces (MVFs) were measured at participants’ shoulder, elbow, and wrist. Fatiguability was also assessed during a repetitive painting task. Participants were asked to assume both slouched and erect spinal postures, in a random order. In the erect posture, participants achieved higher shoulder and elbow isometric MVF levels and took longer to reach a fatigue threshold. Thus, spinal posture tends to remotely influence upper limb functional capacities, especially at the shoulder and elbow. Ergonomists should consider spinal posture even when focusing on musculoskeletal disorders of the upper limb.

Strength Asymmetries Are Muscle-Specific and Metric-Dependent.

We investigated if dominance affected upper limbs muscle function, and we calculated the level of agreement in asymmetry direction across various muscle-function metrics of two heterologous muscle groups. We recorded elbow flexors and extensors isometric strength of the dominant and non-dominant limb of 55 healthy adults. Participants performed a series of explosive contractions of maximal and submaximal amplitudes to record three metrics of muscle performance: maximal voluntary force (MVF), rate of force development (RFDpeak), and RFD-Scaling Factor (RFD-SF). At the population level, the MVF was the only muscle function that showed a difference between the dominant and non-dominant sides, being on average slightly (3–6%) higher on the non-dominant side. At the individual level, the direction agreement among heterologous muscles was poor for all metrics (Kappa values ≤ 0.15). When considering the homologous muscles, the direction agreement was moderate between MVF and RFDpeak (Kappa = 0.37) and low between MVF and RFD-SF (Kappa = 0.01). The asymmetries are muscle-specific and rarely favour the same side across different muscle-performance metrics. At the individual level, no one side is more performative than the other: each limb is favoured depending on muscle group and performance metric. The present findings can be used by practitioners that want to decrease the asymmetry levels as they should prescribe specific exercise training for each muscle.

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

PurposeThis 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.MethodsMVIC 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.ResultsMVIC, 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).ConclusionDownhill 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.

Resistance exercise with different workloads have distinct effects on cellular respiration of peripheral blood mononuclear cells.

Little is known how acute exercise‐induced inflammation and metabolic stress affect immune cell bioenergetics and the portion of its components. Therefore, we investigated acute effects of eccentric‐only (E), concentric‐only (C) and combined eccentric‐concentric resistance exercise (E + C) bouts on cellular respiration of peripheral blood mononuclear cells (PBMCs). Twelve strength‐trained young men performed bench press resistance exercises in randomized order. Venous blood samples were drawn at pre‐, 5 min post‐ and 24 h post‐exercise. Several PBMC respiration states were measured using high‐resolution respirometry. Levels of leukocytes, interleukin 6 (IL‐6), C‐reactive protein (CRP), creatine kinase (CK), blood lactate and maximum voluntary isometric force were measured from the same time points. Effects of blood lactate and pH change on bioenergetics of PBMCs were investigated ex vivo. PBMC routine respiration (p = 0.017), free routine capacity (p = 0.025) and ET‐capacity (p = 0.038) decreased immediately after E + C. E responded in opposite manner 5 min post‐exercise compared to E + C (p = 0.013) and C (p = 0.032) in routine respiration, and to E + C in free routine activity (p = 0.013). E + C > C > E was observed for increased lactate levels and decreased isometric force that correlated with routine respiration (R = −0.369, p = 0.035; R = 0.352, p = 0.048). Lactate and pH change did not affect bioenergetics of PBMCs. Acute resistance exercise affected cellular respiration of PBMCs, with training volume and the amount of metabolic stress appear influential. Results suggest that acute inflammation response does not contribute to changes seen in cellular respiration, but the level of peripheral muscle fatigue and metabolic stress could be explaining factors.

Does neuromuscular fatigue generated by trail running modify foot-ground impact and soft tissue vibrations?

ABSTRACT The purpose of the study was to assess the influence of a preceding mountain ultramarathon on the impact between the foot and the ground and the resulting soft tissue vibrations (STV). Two sessions of measurements were performed on 52 trail runners, before and just after mountain trail running races of various distances (from 40 to 171 km). Triaxial accelerometers were used to quantify the foot-ground impact (FGI) and STV of both gastrocnemius medialis (GAS) and vastus lateralis (VL) muscles during level treadmill running at 10 km·h−1. A continuous wavelet transform was used to analyze the acceleration signals in the time–frequency domain, and the maps of coefficients as well as the frequency and damping properties of STV were computed. Fatigue was assessed from isometric maximal voluntary contraction force loss of knee extensors (KE) and plantar flexors (PF) after each race. Statistical nonParametric Mapping and linear mixed models were used to compare the means between the data obtained before and after the races. FGI amplitude and GAS STV were not modified after the race, while VL STV amplitude, frequency and damping significantly decreased whatever the running distance. A significant force loss was observed for the PF (26 ± 14%) and KE (27 ± 16%), but this was not correlated to the changes observed in STV. These results might reveal a protection mechanism of the muscles, indicating that biomechanical and/or physiological adaptations may occur in mountain ultramarathons to limit STV and muscle damage of knee extensors. Trial registration: ClinicalTrials.gov identifier: NCT04025138..

Etiology and Recovery of Neuromuscular Function Following Academy Soccer Training.

Aim: To profile the etiology and recovery time-course of neuromuscular function in response to a mixed-content, standard training week in professional academy soccer players. We concurrently examined physical performance, cognitive function, and perceptual measures of mood and wellness states to identify a range of simple tests applied practitioners could use in the field as surrogate measures of neuromuscular function. Methods: Sixteen professional academy soccer players completed a range of neuromuscular, physical, perceptual, mood, and cognitive function tests at baseline and after a strenuous training day (pitch and gym), with retest at 24, 48, and 72 h, and further pitch and gym sessions after 48 h post-baseline. Maximal voluntary contraction force (MVC) and twitch responses to electrical stimulation (femoral nerve) during isometric knee-extensor contractions and at rest were measured to assess central nervous system (voluntary activation, VA) and muscle contractile (potentiated twitch force, Qtw,pot) function. Results: Strenuous training elicited decrements in MVC force post-session (−11%, p = 0.001) that remained unresolved at 72 h (−6%, p = 0.03). Voluntary activation (motor nerve stimulation) was reduced immediately post-training only (−4%, p = 0.03). No change in muscle contractile function (Qtw,pot) was observed post-training, though was reduced at 24 h (−13%, p = 0.01), and had not fully recovered 72 h after (−9%, p = 0.03). Perceptions of wellness were impaired post-training, and recovered by 24 h (sleepiness, energy) and 48 h (fatigue, muscle soreness, readiness to train). Countermovement jump performance declined at 24 h, while RSI (Reactive Strength Index) decrements persisted at 48 h. No changes were evident in adductor squeeze, mood, or cognitive function. Conclusion: Elite youth soccer training elicits substantial decrements in neuromuscular function, which are still present 72 h post-strenuous exercise. Though central processes contribute to post-exercise neuromuscular alterations, the magnitude and prolonged presence of impairments in contractile function indicates it is the restitution of muscular function (peripheral mechanisms) that explains recovery from strenuous training in academy soccer players.

A Low-Cost Wireless Bite Force Measurement Device.

Assessing maximum voluntary bite force is important to characterize the functional state of the masticatory system. Due to several factors affecting the estimation of the maximum bite force, a unique solution combining desirable features such as reliability, accuracy, precision, usability, and comfort is not available. The aim of the present study was to develop a low-cost bite force measurement device allowing for subject-specific customization, comfortable bite force expression, and reliable force estimation over time. The device was realized using an inexpensive load cell, two 3D printed ergonomic forks hosting reusable subject-specific silicone molds, a read-out system based on a low-cost microcontroller, and a wireless link to a personal computer. A simple model was used to estimate bite force taking into account individual morphology and device placement in the mouth. Measurement reliability, accuracy, and precision were assessed on a calibration dataset. A validation procedure on healthy participants was performed to assess the repeatability of the measurements over multiple repetitions and sessions. A 2% precision and 2% accuracy were achieved on measurements of forces in the physiological range of adult bite forces. Multiple recordings on healthy participants demonstrated good repeatability (coefficient of variation 11%) with no significant effect of repetition and session. The novel device provides an affordable and reliable solution for assessing maximum bite force that can be easily used to perform clinical evaluations in single sessions or in longitudinal studies.

Operation behaviours of surgical forceps in continuous curvilinear capsulorhexis.

Continuous curvilinear capsulorhexis (CCC) is a delicate ophthalmic procedure which may benefit from robot technology. Measuring the behaviours (physiological tremor, operation force) of surgeons provides baseline data to develop assistive CCC robot. A forceps with fibre bragg grating and inertial sensors is used to measure the surgeons' behaviours while experts/novices perform CCC on ex-vivo pig eyes, in-vivo rabbit eyes and ex-vivo human lens. In pig/rabbit tests, the root-mean-square (RMS) tremor amplitude is 35.26/59.04μm (expert/novice, transverse), 13.3/20.55μm (axial). The RMS voluntary force (VF) and involuntary force (IF) are 8.97/17.16mN, and 0.66/1.90mN, respectively. In human lens test, the RMS tremor amplitude is 24.0μm (transverse, expert only), 9.88μm (axial). The RMS VF and RMS IF are 9.04mN (expert only) and 0.17mN, respectively. The expert surgeons have better precision and less operation force.

Faster early rate of force development in warmer muscle: an in vivo exploration of fascicle dynamics and muscle-tendon mechanical properties.

Although heat exposure has been shown to increase the skeletal rate of force development (RFD), the underlying processes remain unknown. This study investigated the effect of heat on gastrocnemius medialis (GM) muscle-tendon properties and interactions. Sixteen subjects performed electrically evoked and voluntary contractions combined with ultrafast ultrasound under thermoneutral [control (CON): 25.8 ± 1.8°C, core temperature 37.0 ± 0.3°C, muscle temperature 34.0 ± 1.1°C] and passive heat exposure [hot (HOT): 47.4 ± 1.8°C, core temperature 38.4 ± 0.3°C, muscle temperature 37.0 ± 0.8°C] conditions. Maximal voluntary force changes did not reach statistical significance (-5.0 ± 11.3%, P = 0.052) whereas voluntary activation significantly decreased (-4.6 ± 8.7%, P = 0.038) in HOT. Heat exposure significantly increased voluntary RFD before 100 ms from contraction onset (+48.2 ± 62.7%; P = 0.013), without further changes after 100 ms. GM fascicle dynamics during electrically evoked and voluntary contractions remained unchanged between conditions. Joint velocity at a given force was higher in HOT (+7.1 ± 6.6%; P = 0.004) but the fascicle force-velocity relationship remained unchanged. Passive muscle stiffness and active tendon stiffness were lower in HOT than CON (P ≤ 0.030). This study showed that heat-induced increases in early voluntary RFD may not be attributed to changes in contractile properties. Late voluntary RFD was unaltered, possibly due to decreased soft tissues' stiffness in heat. Further investigations are required to explore the influence of neural drive and motor unit recruitment in the enhancement of explosive strength elicited by heat exposure.

Growth curves for mandibular range of motion and maximum voluntary bite force in healthy children.

Mandibular range of motion and bite force are indispensable variables for the evaluation of mandibular function. There are a variety of medical and dental conditions that can negatively affect mandibular function. Values for mandibular range of motion (i.e., active and passive maximum interincisal mouth opening, protrusion, and laterotrusion) and anterior maximum voluntary bite force (AMVBF) in healthy children and adolescents can help in recognizing temporomandibular dysfunction. In this longitudinal study, 169 healthy children aged 6–18 years were included. They were examined at four time points over 1 year. Mixed model analysis was performed to produce growth curves of mandibular range of motion and AMVBF. Average active maximum interincisal mouth opening was significantly higher in boys with 50.0 mm compared to 47.8 mm in girls. Boys also had a significantly higher AMVBF than girls with an average of 169.0 N versus 140.0 N, respectively. Growth curves of active and passive maximum interincisal mouth opening showed an increase with age, albeit levelling off through puberty. The growth curves of AMVBF in girls reach a plateau phase at ages 12–14 years, after which the curve descends; in boys, the AMVBF tended to increase up to 18 years of age, although a slow‐down after 14 years of age was noted.

Effect of Caffeine Ingestion on Indirect Markers of Exercise-Induced Muscle Damage: A Systematic Review of Human Trials.

The effect of caffeine on mitigating exercise-induced muscle damage (EIMD) is still poorly understood, but it was hypothesized that caffeine could contribute to decreasing delayed onset muscle soreness, attenuating temporary loss of strength, and reducing circulating levels of blood markers of muscle damage. However, evidence is not conclusive and beneficial effects of caffeine ingestion on EIMD are not always observed. Factors, such as the type of exercise that induces muscle damage, supplementation protocol, and type of marker analyzed contribute to the differences between the studies. To expand knowledge on the role of caffeine supplementation in EIMD, this systematic review aimed to investigate the effect of caffeine supplementation on different markers of muscle damage. Fourteen studies were included, evaluating the effect of caffeine on indirect muscle damage markers, including blood markers (nine studies), pain perception (six studies), and MVC maximal voluntary contraction force (four studies). It was observed in four studies that repeated administration of caffeine between 24 and 72 h after muscle damage can attenuate the perception of pain in magnitudes ranging from 3.9% to 26%. The use of a single dose of caffeine pre-exercise (five studies) or post-exercise (one study) did not alter the circulating blood levels of creatine kinase (CK). Caffeine supplementation appears to attenuate pain perception, but this does not appear to be related to an attenuation of EIMD, per se. Furthermore, the effect of caffeine supplementation after muscle damage on strength recovery remains inconclusive due to the low number of studies found (four studies) and controversial results for both dynamic and isometric strength tests.

Modulation of subjective peripheral sensation, F-waves, and somatosensory evoked potentials in response to unilateral pinch task measured on the contractile and non-contractile sides.

Depression of the sensory input during voluntary muscle contractions has been demonstrated using electrophysiological methods in both animals and humans. However, the association between electrophysiological responses of the sensory system and subjective peripheral sensation (SPS) during a voluntary muscle contraction remains unclear. This study aimed to describe the changes in SPS, spinal α-motoneuron excitability (F-wave to M-wave amplitude), and somatosensory evoked potentials (SEPs) during a unilateral pinch-grip task. Outcome variables were measured on the side ipsilateral and contralateral to the muscle contraction and at rest (control). Participants were 8 healthy men aged 20.9±0.8 years. The isometric pinch-grip task was performed at 30% of the maximum voluntary isometric force measured for the right and left hands separately. The appearance rate of the F-wave during the task was significantly higher for the ipsilateral (right) hand than for the contralateral (left) hand and control condition. Although there was no difference in the F-wave latency between hands and the control condition, the amplitude of the F-wave was significantly higher for the ipsilateral (right) hand than for the contralateral (left) hand and the control condition. There was no difference in the amplitude of the SEP at N20. However, the amplitude at P25 was significantly lower for the ipsilateral (right) hand than for the contralateral (left) hand and the control condition. The accuracy rate of detecting tactile stimulation, evaluated for 20 repetitions using a Semmes–Weinstein monofilament at the sensory threshold for each participant, was significantly lower during the pinch-grip task for both the ipsilateral (right) and contralateral (left) hands than in the control condition. Overall, our findings show that SPS and neurophysiological parameters were not modulated in parallel during the task, with changes in the subjective sensation preceding changes in electrophysiological indices during the motor task. Our findings provide basic information on sensory-motor coordination.

Mechanisms of Neuromuscular Fatigability in People with Cancer-Related Fatigue.

Cancer-related fatigue (CRF) is a debilitating symptom that affects around one-third of people for months or years after cancer treatment. In a recent study, we found that people with posttreatment CRF have greater neuromuscular fatigability. The aim of this secondary analysis was to examine the etiology of neuromuscular fatigability in people with posttreatment CRF. Ninety-six people who had completed cancer treatment were dichotomized into two groups (fatigued and nonfatigued) based on a clinical cut point for fatigue. Alterations in neuromuscular function (maximal voluntary contraction peak force, voluntary activation, potentiated twitch force, and EMG) in the knee extensors were assessed across three common stages of an incremental cycling test. Power outputs during the fatigability test were expressed relative to gas exchange thresholds to assess relative exercise intensity. The fatigued group had a more pronounced reduction in maximal voluntary contraction peak force and potentiated twitch force throughout the common stages of the incremental cycling test (main effect of group: P < 0.001, ηp2 = 0.18 and P = 0.029, ηp2 = 0.06, respectively). EMG was higher during cycling in the fatigued group (main effect of group: P = 0.022, ηp2 = 0.07). Although the relative intensity of cycling was higher in the fatigued group at the final common stage of cycling, this was not the case during the initial two stages, despite the greater impairments in neuromuscular function. Our results suggest that the rapid impairments in neuromuscular fatigability in people with CRF were primarily due to disturbances at the level of the muscle rather than the central nervous system. This could affect the ability to tolerate daily physical activities.