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Objective: The primary objective of this study was to assess the impact of high-intensity deep squat training integrated with various blood flow restriction (BFR) modalities on the activation of lower limb and core muscles. Methods: A randomized, self-controlled crossover experimental design was employed with 12 participants. The exercise protocol consisted of squat training at 75% of one-repetition maximum (1RM), performed in 3 sets of 8 repetitions with a 2-min inter-set rest period. This was conducted under four distinct BFR conditions: continuous low BFR (T1), intermittent medium BFR (T2), intermittent high BFR (T3), and a non-restricted control (C). Surface electromyography (EMG) was utilized to collect EMG signals from the target muscles during the BFR and squat training sessions. The root mean square (RMS) amplitude standard values were calculated for each squat set to quantify muscle activation levels, with these values expressed as a percentage of the maximum voluntary contraction (%MVC). Rating of Perceived Exertion was evaluated after each squat set, and leg circumference measurements were taken. Results: 1) During the first two sets of deep squats, the %MVC of the vastus lateralis and vastus medialis in all compression groups was significantly higher than that in the control group (p < 0.05). Furthermore, in the first set, the %MVC of the vastus lateralis in Group T3 was significantly higher than in Group T2 (p < 0.05). In the third set, the %MVC of the vastus medialis in Groups T1 and T3 was significantly lower than in the first two sets (p < 0.05). 2) Group T1 showed an increased activation of the biceps femoris and semitendinosus muscles in the second and third sets, with %MVC values significantly greater than in the first set (p < 0.05). Group T2 only showed an increase in biceps femoris activation in the third set (p < 0.05). Group T3 significantly increased the activation of the biceps femoris and semitendinosus muscles only in the first set (p < 0.05). 3) No significant differences were observed in the changes of rectus abdominis %MVC among the groups (p > 0.05). In the first set, Group T3's erector spinae %MVC was significantly higher than the control group's; in the second set, it was significantly higher than both Group T2 and the control group's (p < 0.05). 4) After training, a significant increase in thigh circumference was observed in all groups compared to before training (p < 0.05). 5) For RPE values, Group T2's post-squat values were significantly higher than the control group's after all three sets (p < 0.05). Group T1's RPE values were also significantly higher than the control group's after the third set (p < 0.05). Groups T1, T2, and C all had significantly higher RPE values in the second and third sets compared to the first set (p < 0.05). Conclusion: All BFR modalities significantly enhanced the activation level of the anterior thigh muscles, with the continuous low BFR mode demonstrating a more stable effect. No significant differences were found in the activation level of the rectus abdominis among the groups. However, the intermittent high BFR mode was the most effective in increasing the activation level of the erector spinae muscles. While BFR did not further augment leg circumference changes, it did elevate subjective fatigue levels. The RPE was lowest during squatting under the intermittent high BFR condition.

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This study investigates gender differences in core muscle morphology among elite alpine skiers using ultrasonography, highlighting significant disparities that could influence training and injury prevention strategies. METHODS: A cross-sectional design was employed, examining ultrasound imaging (USI) in 22 elite skiers (11 male, 11 female) to assess the thickness of the external oblique (EO), internal oblique (IO), transversus abdominis (TrAb), and rectus abdominis (RA) muscles. RESULTS: Significant differences were noted, with male skiers displaying greater muscle thickness, particularly in the right IO and RA and left IO, EO, TrAb, and RA. CONCLUSIONS: These findings suggest that male and female skiers may require different training approaches to optimize performance and reduce injury risks. This research contributes to a deeper understanding of the physical demands on elite skiers and underscores the need for gender-specific training regimens to enhance athletic outcomes and prevent injuries.

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Dynamic muscular workload assessments of tractor operators are rarely studied or documented, which is critical to improving their performance efficiency and safety. A study was conducted to assess and model dynamic load on muscles, physiological variations, and discomfort of the tractor operators arriving from the repeated clutch and brake operations using wearable non-invasive ergonomic transducers and data-run techniques. Nineteen licensed tractor operators operated three different tractor types of varying power ranges at three operating speeds (4-5 km/h), and on two common operating surfaces (tarmacadam and farm roads). During these operations, ergonomic transducers were utilized to capture the load on foot muscles (gastrocnemius right [GR] and soleus right [SR] for brake operation and gastrocnemius left [GL], and soleus left [SL] for clutch operation) using electromyography (EMG). Forces exerted by the feet during brake and clutch operations were measured using a custom-developed foot transducer. During the process, heart rate (HR) and oxygen consumption rates (OCR) were also measured using HR monitor and K4b2 systems, and energy expenditure rate (EER) was determined using empirical equation. Post-tractor operation cycle, an overall discomfort rating (ODR) for that operation was manually recorded on a 10-point psychophysical scale. EMG-based maximum volumetric contraction (%MVC) measurements revealed higher strain on GR (%MVC = 43%), GL (%MVC = 38%), and SR (%MVC = 41%) muscles which in normal conditions should be below 30%. The clutch and brake actuation forces were recorded in the ranges of 90-312 N and 105-332 N, respectively and were significantly affected by the operating speed, tractor type, and operating surface (p < 0.05). EERs of the operators were measured in the moderate-heavy to heavy ranges (9-24 kJ/min) during the course of trials, suggesting the need to refine existing clutch and brake system designs. Average operator ODR responses indicated 7.8% operations in light, 48.5% in light-moderate, 25.2% in moderate, 10.7% in moderate-high, and 4.9% operations in high discomfort categories. When evaluated for the possibility of minimizing the number of transducers for physical workload assessment, EER showed moderate-high correlations with the EMG signals (rGR = 0.78, rGL = 0.75, rSR = 0.68, rSL = 0.66). Similarly, actuation forces had higher correlations with EMG signals for all the selected muscles (r = 0.70-0.87), suggesting the use of simpler transducers for effective operator workload assessment. As a means to minimize subjectivity in ODR responses, machine learning algorithms, including K-nearest neighbor (KNN), random forest classifier (RFC), and support vector machine (SVM), predicted the ODR using body mass index (BMI), HR, EER, and EMG at high accuracies of 87-97%, with RFC being the most accurate. Such high-throughput and data-run ergonomic evaluations can be instrumental in reconsidering workplace designs and better fits for end-users in terms of agricultural tractors and machinery systems.

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Skin autofluorescence is a useful index to estimate the accumulation of advanced glycation end-products in human tissues. Elderly persons with higher skin autofluorescence have lower muscle mass, muscle strength and muscle power, however, little is known about the relationship between the skin autofluorescence level and each muscle activity. We measured the values of skin autofluorescence from five places on a lower limb, and the signals of surface electromyogram during isometric contractions from five muscles on that, simultaneously. The waveforms of surface electromyogram were analyzed by Daubechies-4 wavelet transformation. The value of skin autofluorescence was increased in the proximal part of the lower limb compared with the value of the distal part. The principal component of surface electromyogram activity in a time-frequency domain was lower in the proximal part compared with that of the distal part. There was a weak negative correlation between the value of skin autofluorescence on the gluteal region and the value of the mean wavelet coefficient of the surface electromyogram signals within the gluteus maximus muscle. The higher accumulation of advanced glycation end-products on the gluteal region might suggest the lower muscle activity in aging without disease and disability.

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Movements of the human biological system have adapted to the physical environment under the 1-g gravitational force on Earth. However, the effects of microgravity in space on the underlying functional neuromuscular control behaviors remain poorly understood. Here, we aimed to elucidate the effects of prolonged exposure to a microgravity environment on the functional coordination of multiple muscle activities. The activities of 16 lower limb muscles of 5 astronauts who stayed in space for at least 3 mo were recorded while they maintained multidirectional postural control during bipedal standing. The coordinated activation patterns of groups of muscles, i.e., muscle synergies, were estimated from the muscle activation datasets using a factorization algorithm. The experiments were repeated a total of five times for each astronaut, once before and four times after spaceflight. The compositions of muscle synergies were altered, with a constant number of synergies, after long-term exposure to microgravity, and the extent of the changes was correlated with the increased velocity of postural sway. Furthermore, the muscle synergies extracted 3 mo after the return were similar in their activation profile but not in their muscle composition compared with those extracted in the preflight condition. These results suggest that the modularity in the neuromuscular system became reorganized to adapt to the microgravity environment and then possibly reoptimized to the new sensorimotor environment after the astronauts were reexposed to a gravitational force. It is expected that muscle synergies can be used as physiological markers of the status of astronauts with gravity-dependent change.NEW & NOTEWORTHY The human neuromuscular system has adapted to the gravitational environment on Earth. Here, we demonstrated that prolonged exposure to a microgravity environment in space changes the functional coordination of multiple muscle activities regarding multidirectional standing postural control. Furthermore, the amount of change led to a greater regulatory balancing activity needed for postural control immediately after returning to Earth and differences in muscular coordination before space flight and 3 mo after the return to Earth.

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BACKGROUND: The leg press is one of the most typical exercises for strengthening the lower limbs. The objectives of this study were to compare 5 inclined leg press exercise conditions, varying the feet width stance (100% or 150% hip width), the feet rotation (0° or 45° external rotation) on the footplate and using 2 different movement velocities (MVs; maximum intended, and 2:2 seconds steady-paced velocities) to determine their effect on muscle activation as well as on the kinematic parameters between trained men and trained women. HYPOTHESES: There will be no significant differences in muscle activation with regard to the feet position. The higher the MV, the greater the muscle activation. STUDY DESIGN: A cross-sectional cohort study. LEVEL OF EVIDENCE: Level 3. METHODS: A repeated-measures between-group design was performed to examine muscle activation and kinematic parameters for the different conditions between gender groups. The level of significance was set at alpha = 0.05 for all statistical analyses. RESULTS: Muscle activation presented no differences between conditions regarding feet width stance or feet rotation. Furthermore, muscle activation was greater during positive phases than negative phases of the exercise for all conditions and was also greater under maximum intended velocity conditions compared with steady-paced conditions. Otherwise, the muscle activation pattern presented slight differences by gender. In men, the greatest muscle activation was for the vastus medialis, followed by the vastus lateralis (VL), rectus femoris (RF), and gluteus medialis (GMED), while in women, the greatest muscle activation was for the vastus medialis, followed by the RF, VL, and GMED. Finally, greater mean propulsive velocity, maximum velocity, maximum power, and footplate displacement values were reported for men than for women under all the conditions. CONCLUSION: The inclined leg press exercise produces the highest muscle activation in the vastus medialis, regardless of the velocity, feet stance, or gender. CLINICAL RELEVANCE: Given that there are no differences in muscle activation regarding the feet stance, a participant's preferred feet stance should be encouraged during the inclined leg press exercise. Furthermore, the MV would preferably depend on the session objective (a training or a rehabilitation program), being aware that there is greater muscle activation at higher speeds. The inclined leg press exercise could be performed as a closed kinetic chain exercise when the main objective is to activate the vastus medialis.

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Paired associative stimulation (PAS) is a non-invasive method to modulate the excitability of the primary motor cortex (M1). PAS involves the combination of peripheral nerve stimulation and transcranial magnetic stimulation (TMS) over the primary motor cortex. However, for lower-limb muscles, PAS has only been applied to the few muscles innervated by peripheral nerves that can easily be stimulated. This study used transcutaneous spinal cord stimulation (tSCS) to the posterior root, stimulating the sensory nerves of multiple lower-limb muscles, and aimed to investigate the effect of PAS consisting of tSCS and TMS on corticospinal excitability. Twelve non-disabled men received 120 paired stimuli on two separate days in (1) an individual-ISI condition, using inter-stimulus intervals (ISIs) of paired stimuli individually calculated to send two signals to M1 with individually-adjusted ISI, and (2) a constant-ISI condition, using a constant ISI of 100 ms. Before and after PAS, corticospinal excitability was assessed in the lower-limb muscles. Facilitation of corticospinal excitability in the lower-leg and hamstring muscles was observed up to 30 min after PAS only in the individual-ISI condition (p < 0.05), although there was no significant difference between the individual-ISI and constant-ISI conditions. Additionally, our results revealed a difference in PAS-induced facilitation among lower-limb muscles, suggesting a spatial gradient of PAS-induced facilitation of corticospinal excitability, such that knee flexor muscles have a higher potential for plastic change than knee extensor muscles. These findings will foster a better understanding of the neural mechanisms underlying PAS-induced neuroplasticity, leading to better neurorehabilitation and motor learning strategies.

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Sarcopenia is a major comorbidity in chronic obstructive pulmonary (COPD). Whether deficient muscle repair mechanisms and regeneration exist in the vastus lateralis (VL) of sarcopenic COPD remains debatable. In the VL of control subjects and severe COPD patients with/without sarcopenia, satellite cells (SCs) were identified (immunofluorescence, specific antibodies, anti-Pax-7, and anti-Myf-5): activated (Pax-7+/Myf-5+), quiescent/regenerative potential (Pax-7+/Myf-5-), and total SCs, nuclear activation (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling [TUNEL]), and muscle fiber type (morphometry and slow- and fast-twitch, and hybrid fibers), muscle damage (hematoxylin-eosin staining), muscle regeneration markers (Pax-7, Myf-5, myogenin, and MyoD), and myostatin levels were identified. Compared to controls, in VL of sarcopenic COPD patients, myostatin content, activated SCs, hybrid fiber proportions, TUNEL-positive cells, internal nuclei, and muscle damage significantly increased, while quadriceps muscle strength, numbers of Pax-7+/Myf-5- and slow- and fast-twitch, and hybrid myofiber areas decreased. In the VL of sarcopenic and nonsarcopenic patients, TUNEL-positive cells were greater, whereas muscle regeneration marker expression was lower than in controls. In VL of severe COPD patients regardless of the sarcopenia level, the muscle regeneration process is triggered as identified by SC activation and increased internal nuclei. Nonetheless, a lower regenerative potential along with significant alterations in muscle phenotype and damage, and increased myostatin were prominently seen in sarcopenic COPD.

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This study examined the characteristics of lower limb muscle activity in elderly persons after ergometric pedaling exercise for 1 month. To determine the effect of the exercise, surface electromyography (SEMG) of lower limb muscles was subjected to Daubechies-4 wavelet transformation, and mean wavelet coefficients were compared with the pre-exercise coefficients and the post-exercise coefficients in each wavelet level. The characteristics of muscle activity after pedaling exercise were also compared between the elderly subjects and young subjects. For the elderly subjects, the mean wavelet coefficients were significantly decreased in the tibialis anterior and the gastrocnemius medialis at wavelet levels of 3, 4, and 5 (125-62.5, 62.5-31.25, and 31.25-15.625 Hz, respectively), by pedaling exercise. However, the mean power of wavelet levels of 2 and 3 (250-125 and 125-62.5 Hz) within the rectus femoris and the biceps femoris were significantly increased in the young subjects. The effect of pedaling exercise is different from the effects of heavy-resistance training. It was suggested that the muscle coordination, motor unit (MU) firing frequency, and firing fiber type of lower limb muscles are changed with the different characteristics between elderly and young persons by pedaling exercise for 1 month.

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BACKGROUND: Surface electromyography (sEMG) can provide information on muscle activation patterns during gait. OBJECTIVES: To characterize electromyographic activity during gait in shallow water and during deep-water running compare to on land and to review and analyse underwater surface-electromyographic (sEMG) procedures. SEARCH METHODS: Eight databases (MEDLINE, EMBASE, WEB OF SCIENCE, SPORT Discus, CINAHL, SCOPUS, SCIELO, and LILACS) were searched from their inception to the December of 2019. SELECTION CRITERIA: The selected studies had to be related to electromyographic analysis of gait in an aquatic environment. DATA COLLECTION AND ANALYSIS: The studies that met the inclusion criteria were reviewed by two independent reviewers and divided into four groups. RESULTS: Ten studies met the inclusion criteria. Lower muscle activation was found with treadmill water walking compared to treadmill land walking. With deep-water running, the leg muscles (tibialis anterior and gastrocnemius lateralis) have lower muscle activation when compared to on land running, but the trunk and thigh muscles have higher activation. CONCLUSION: If gait is performed on an aquatic treadmill, the muscles assessed had lower muscle activation when compared to land. During deep-water running activities, lower activation of the distal leg muscles and a higher activation thigh muscles were found when compared to on land. Studies did not follow standard processes in sEMG procedures.

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OBJECTIVES: The excitability of some neural circuits involved in walking and affected in individuals with chronic stroke can be modulated during and/or immediately after anodal transcranial direct current stimulation (a-tDCS). This study was designed to investigate the effects of a-tDCS during and immediately after application on leg muscle activity during gait, and on spatiotemporal and kinematic gait parameters in patients with chronic stroke. METHODS: This study was randomized, sham-controlled and double-blinded with a cross-over design and included 24 individuals with chronic stroke. Each participant underwent one 30-minute session each of effective a-tDCS at 2mA and sham tDCS. In both sessions, the anode was placed over the leg motor cortex of the affected hemisphere and the cathode over the contralateral orbit. Six gait trials were performed before, during and immediately after each effective/sham tDCS session. Electromyographic activity of leg muscles, as well as spatiotemporal (e.g. gait speed) and kinematic (e.g. peak knee flexion and ankle dorsiflexion in the swing phase of gait) gait parameters were recorded. Genotyping for the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism was undertaken since this gene may influence motor skill learning and the effects of tDCS. RESULTS: No significant effects of a-tDCS on gait parameters were found either for the total group or for the Val66Met (N=10) and Val66Val (N=14) subgroups. CONCLUSION: A single session of a-tDCS delivered to the leg motor cortex did not immediately improve gait parameters in individuals with chronic stroke, regardless of their BDNF genotype.

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Impaired muscle strength and mass (sarcopenia) are common in patients with respiratory cachexia, namely chronic obstructive pulmonary disease (COPD) and in lung cancer (LC)-cachexia. Misfolded/unfolded proteins in endoplasmic reticulum (ER) induce the compensatory unfolded protein response (UPR). Expression of ER stress and UPR markers may be differentially upregulated in vastus lateralis (VL) of patients with respiratory sarcopenia associated with either a chronic condition (COPD) or subacute (LC)-cachexia. In VL specimens from 40 COPD patients (n = 21, sarcopenic, fat-free mass index [FFMI] 16 kg/m2 and n = 19, nonsarcopenic, FFMI 18 kg/m2 ), 13 patients with LC-cachexia (FFMI 17 kg/m2 ), and 19 healthy controls (FFMI 19 kg/m 2 ), expression markers of ER stress, UPR (protein kinase-like ER kinase [PERK], activating transcription factor [ATF] 6, and inositol-requiring enzyme [IRE] 1-α), oxidative stress, autophagy, proteolysis, and apoptosis (reverse transcription polymerase chain reaction and immunoblotting), and fiber atrophy (histology) were assessed. Atrophy and muscle wasting and weakness were seen in both groups of sarcopenic patients. Compared to healthy controls, in muscles of LC-cachexia patients, expression of ER stress markers and UPR (three arms) was significantly upregulated, while in sarcopenic COPD, expression of a few ER stress markers and IRE1-α arm was upregulated. ER stress and an exaggerated UPR were observed in the VL muscle of patients with respiratory sarcopenia. The three branches of UPR were similarly upregulated in muscles of cancer cachectic patients, whereas in sarcopenic COPD patients, only IRE1 was upregulated. The differential profile of muscle UPR in chronic and subacute respiratory conditions offers a niche for the design of specific novel therapeutic approaches.

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Exercise-based training decreases hospitalizations in heart failure patients but such patients have exercise intolerance. The objectives of the study were to evaluate the effect of 12 weeks of Tai Chi exercise and lower limb muscles' functional electrical stimulation in older chronic heart failure adults. A total of 1,084 older adults with chronic systolic heart failure were included in a non-randomized clinical trial (n=271 per group). The control group did not receive any kind of intervention, one group received functional electrical stimulation of lower limb muscles (FES group), another group practiced Tai Chi exercise (TCE group), and another received functional electrical stimulation of lower limb muscles and practiced Tai Chi exercise (FES & TCE group). Quality of life and cardiorespiratory functions of all patients were evaluated. Compared to the control group, only FES group had increased Kansas City Cardiomyopathy Questionnaire (KCCQ) score (P<0.0001, q=9.06), only the TCE group had decreased heart rate (P<0.0001, q=5.72), and decreased peak oxygen consumption was reported in the TCE group (P<0.0001, q=9.15) and FES & TCE group (P<0.0001, q=10.69). FES of lower limb muscles and Tai Chi exercise can recover the quality of life and cardiorespiratory functions of older chronic heart failure adults (trial registration: Research Registry 4474, January 1, 2015).

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INTRODUCTION: Chronic obstructive pulmonary disease (COPD) is a common preventable and treatable disease and a leading cause of morbidity and mortality worldwide. In COPD, comorbidities, acute exacerbations, and systemic manifestations negatively influence disease severity, prognosis, and progression regardless of the respiratory condition. AREAS COVERED: Several factors and biological mechanisms are involved in the pathophysiology of COPD muscle dysfunction. The non-coding microRNAs were shown to be differentially expressed in the respiratory and limb muscles of patients with COPD. Moreover, a differential expression profile of muscle-specific microRNAs has also been demonstrated in the lower limb muscles of COPD patients with and without muscle mass loss and weakness. All these features are reviewed herein. The most relevant articles on the topic in question were selected from PubMed to write this review. Expert commentary: MicroRNAs are excellent targets for the design of specific therapeutic interventions in patients with muscle weakness. Selective enhancers of microRNAs that promote myogenesis (proliferation and differentiation of satellite cells) should be designed to alleviate the negative impact of skeletal muscle dysfunction and mass loss in COPD regardless of the degree of the airway obstruction.

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PURPOSE: The aim of this study was to evaluate concomitantly the changes in leg-spring behavior and the associated modifications in the lower limb muscular activity during a constant pace run to exhaustion at severe intensity. METHODS: Twelve trained runners performed a running test at the velocity associated with VO(2max) (5.1 ± 0.3 ms(-1); mean time to exhaustion: 353 ± 69s). Running step spatiotemporal parameters and spring-mass stiffness were calculated from vertical and horizontal components of ground reaction force measured by a 6.60 m long force platform system. The myoelectrical activity was measured by wireless surface electrodes on eight lower limb muscles. RESULTS: The leg stiffness decreased significantly (-8.9%; P<0.05) while the vertical stiffness did not change along the exhaustive exercise. Peak vertical force (-3.5%; P<0.001) and aerial time (-9.7%; P<0.001) decreased and contact time significantly increased (+4.6%; P<0.05). The myoelectrical activity decreased significantly for triceps surae but neither vastus medialis nor vastus lateralis presented significant change. Both rectus and biceps femoris increased in the early phase of swing (+14.7%; P<0.05) and during the pre-activation phase (+16.2%; P<0.05). CONCLUSION: The decrease in leg spring-stiffness associated with the decrease in peak vertical ground reaction force was consistent with the decline in plantarflexor activity. The biarticular rectus femoris and biceps femoris seem to play a major role in the mechanical and spatiotemporal adjustments of stride pattern with the occurrence of fatigue during such exhaustive run.

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Objective To observe the surface electromyogram(sEMG)characteristics of the lower limbs muscles in stroke patients and healthy subjects during the passive and active-assisted anti-resistance movements.Methods Twenty four stroke patients and 17 healthy individuals(control group) participated in this study.sEMG of rectus femoris(RF),vastus lateralis(VL),ventralis medialis(VM)and biceps femoris(BF)was recorded during passive and active-assisted anti-resistance of knee joint in both groups.Average EMG(AEMG),mean power frequency(MPF)and median frequency(MF) were analyzed.Results Multiple factor ANOVA showed that very significant differences in the values of MF,MPF and AEMG between non-paretic and the paretic limbs appeared(P

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Task-dependent changes in the cutaneous reflex in the upper and lower leg muscles were examined in normal human subjects (n=11) . After instruction, the subjects were asked to selectively contract agonist muscles (SC task) and to co-contract antagonistic muscles (CC task) for the ankle or knee joint while standing. The cutaneous reflex was elicited by applying non-noxious electrical stimulation to the superficial peroneal nerve at the ankle joint (200 Hz, 5 pulses) . The EMG signal was rectified, averaged (n=10), cumulatively summated up to 150ms after the end of the stimulation artifact, and then divided by the time interval for the summation (ACRE<SUB>150</SUB>) . A strong inhibitory effect was determined at a latency of 50 ms and was followed by a facilitatory effect after the electrical stimulation during the SC task in all muscles. In contrast, it was found that the early inhibition and the later facilitation tended to be decreased and increased during the cc task, respectively. A linear regression analysis between the ACRE<SUB>150</SUB> and the background EMG revealed that the regression slopes were significantly decreased during CC task except for the tibialis anterior (TA) and biceps femoris. The reflex ratio (ACRE<SUB>150</SUB>/background EMG) was also negative for the SC task in all muscles tested, but was significantly reduced or showed a positive value for the CC task. These results suggest that the brain may control the cutaneous reflex pathways to enhance the facilitatory effects of the thigh and ankle extensor muscles during the CC task. This reflex action during the CC task may serve to prevent an undesirable fall in the center of gravity in response to a sudden tactile sensation to the dorsal surface of the foot.