Estimates of persistent inward currents in lower limb motoneurons are larger in females than in males.

Noninvasive recordings of motor unit (MU) spike trains help us understand how the nervous system controls movement and how it adapts to various physiological conditions. The majority of participants in human and nonhuman animal physiology studies are male, and it is assumed that mechanisms uncovered in these studies are shared between males and females. However, sex differences in neurological impairment and physical performance warrant the study of sex as a biological variable in human physiology and performance. To begin addressing this gap in the study of biophysical properties of human motoneurons, we quantified MU discharge rates and estimates of persistent inward current (PIC) magnitude in both sexes. We decomposed MU spike trains from the tibialis anterior (TA), medial gastrocnemius (MG), and soleus (SOL) using high-density surface electromyography and blind source separation algorithms. Ten participants of each sex performed slow triangular (10 s up and down) isometric contractions to a peak of 30% of their maximum voluntary contraction. We then used linear mixed-effects models to determine if peak discharge rate and estimates of PICs were predicted by the fixed effects of sex, muscle, and their interaction. Despite a lack of sex-differences in peak discharge rates across all muscles, estimates of PICs were larger [χ2(1) = 6.26, P = 0.012] in females [4.73 ± 0.242 pulses per second (pps)] than in males (3.81 ± 0.240 pps). These findings suggest that neuromodulatory drive, inhibitory input, and/or biophysical properties of motoneurons differ between the sexes and may contribute to differences in MU discharge patterns.NEW & NOTEWORTHY Sex-related differences in motoneuron analyses have emerged with greater inclusion of female participants, however, mechanisms for these differences remain unclear. Estimates of persistent inward currents (i.e., ΔF) in motoneurons of the lower limb muscles were larger in females than in males. This suggests neuromodulatory drive, monoaminergic signaling, intrinsic motoneuron properties, and/or descending motor commands may differ between the sexes, which provides a potential mechanism underlying previously reported sex-related differences in motoneuron discharge patterns.

Relationship between the hsa miR 150-5p and FTO gene expression in white subcutaneous adipose tissue with overweight/obesity, lipid profile and glycemia.

The overweight population is growing in the world, and the search for obesity-associated mechanisms is important for a better understanding of this disease. Few studies with the FTO gene and miRs show how they associate to obesity and how they can impact this disease. The aim of this study was to verify the relationship between the FTO gene and the hsa-miR-150-5p expression with overweight/obesity, lipid profile, and fast blood glucose. Men and women (18 years older or above), with body mass index ≥ 18.5 kg/m2, were enrolled in the present study and the FTO gene and hsa-miR-150-5p expression, biochemical parameters of blood and anthropometric measurements were analyzed. The results highlight that the FTO gene expression is associated to obesity (p 0.029), LDL-C (p 0.02) and fasting blood glucose (p 0.02), but not with triglycerides (p 0.69), total cholesterol (p 0.21), and HDL-C (p 0.24). The hsa-miR-150-5p is not associated to obesity (p 0.84), triglycerides (p 0.57), total cholesterol (p 0.51), HDL-C (p 0.75), LDL-C (p 0.32), and fasting blood glucose (p 0.42). The FTO gene expression is related to obesity, LDL-C and blood fasting glucose, representing a good molecular marker for obesity.

No-load resistance training as a promising alternative to stop detraining period due to covid-19 lockdown in older adults - Case report.

Restrictions to control the COVID-19 pandemic have caused older adults to stop their usual activities, including physical exercises. The novel approach of isometric no-load resistance training (NLRT) can be an interesting alternative to conventional training to oppose the harmful effects of detraining. We described the design and preliminary evaluation of an eight-week, twice-weekly NLRT program for older adults returning to strength training programs after COVID-19 lockdown. An older woman (66 years, 61.9kg, 158.5cm) and an older man (66 years, 84.1kg, 166.5cm) who were engaged in conventional strength training programs before the first COVID-19 lockdown participated in this case study. We collected muscle thickness measures using a B-mode ultrasound imaging and maximum isometric torque using an isokinetic dynamometer. Our results revealed that NLRT seems to be a good alternative to increase muscle thickness of knee and elbow flexors and extensors muscles in older adults. However, NLRT effects were inconsistent for maximum torque.

Voluntary co-contraction of ankle muscles alters motor unit discharge characteristics and reduces estimates of persistent inward currents.

Motoneuronal persistent inward currents (PICs) are both facilitated by neuromodulatory inputs and highly sensitive to local inhibitory circuits (e.g., Ia reciprocal inhibition). Methods aimed to increase group Ia reciprocal inhibition from the antagonistic muscle have been successful in decreasing PICs, and the diffuse actions of neuromodulators released during activation of remote muscles have increased PICs. However, it remains unknown how motoneurons function in the presence of simultaneous excitatory and inhibitory commands. To probe this topic, we investigated motor unit (MU) discharge patterns and estimated PICs during voluntary co-contraction of ankle muscles, which simultaneously demands the contraction of agonist-antagonist pairs. Twenty young adults randomly performed triangular ramps (10s up and down) of both co-contraction (simultaneous dorsiflexion and plantarflexion) and isometric dorsiflexion to a peak of 30% of their maximum muscle activity from a maximal voluntary contraction. Motor unit spike trains were decomposed from high-density surface electromyography recorded over the tibialis anterior (TA) using blind source separation algorithms. Voluntary co-contraction altered motor unit discharge rate characteristics, decreasing estimates of PICs by 20% (4.47 pulses per second (pps) vs 5.57 pps during isometric dorsiflexion). These findings suggest that, during voluntary co-contraction, the inhibitory input from the antagonist muscle overcomes the additional excitatory and neuromodulatory drive that may occur due to the co-contraction of the antagonist muscle, which constrains PIC behavior.

Muscle Recruitment Strategies in a Redundant Task: Age Differences Through Network Analyses.

There are numerous studies comparing young and old adults in terms of muscle coordination in standard tasks (e.g., walking, reaching) and small variations of them. These tasks might hide differences: individuals would converge to similar behavior as they practice these throughout life. Also, we are unaware of studies that considered the muscle recruitment nested dynamics. For this reason, our study evaluated how young and old women coordinate and control the movement system while performing an unusual redundant motor control task through the network physiology approach. We acquired electromyographic signals from nine leg muscles of the dominant and non-dominant limbs during maximum voluntary isometric contractions (knee extension and flexion) and co-contraction bouts. Our results showed that young participants presented higher peak torque output, with similar EMG variability, compared to older participants. Considering firing rate frequencies, old and young women demonstrated different traits for network clustering and efficiency for the task. Age seems to affect muscle coordination at higher frequencies, even with a similar number of muscle synergies, indicating that younger women might have more integrated synergies than older women. The findings also point to differential muscle coordination adaptability.

Myoelectric activity and improvements in strength and hypertrophy are unaffected by the ankle position during prone leg curl exercise - a within person randomized trial.

To examine the effect of ankle position (i.e. gastrocnemius muscle length) on training outcomes during leg curl exercise, we recruited untrained and trained healthy adults to participate in two separate experiments. In Experiment 1, we studied the acute influence of ankle position on knee flexor myoelectric (EMG) activity during leg curl exercise in a group of trained and a separate group of untrained adults. In Experiment 2, we studied the effects of ankle position on knee flexors muscle thickness and torque across a 10-week training protocol in trained adults. We hypothesized that leg curl exercise with the ankle in a plantarflexed position would enhance EMG activity, muscular strength, and hamstrings muscle thickness. We randomized the legs within a person to perform leg curl exercise with one in a plantarflexed position and the other in a dorsiflexed position. Experiment 1 revealed no significant differences between ankle positions in the EMG activity of hamstring muscle in either group (all p > 0.05). Experiment 2 revealed a significant pre- to post-intervention increase in biceps femoris long head (BFLH) muscle thickness (p = 0.026) and isometric torque (p = 0.03), but there were no significant effects of the ankle position (p = 0.596) or interaction between ankle position and timepoint for these variables (p = 0.420). In sum, the ankle position did not have acute effects on hamstrings EMG activity, nor did it affect strength and hypertrophy adaptations after 10-weeks of leg curl exercise training. Interestingly, however, the limb which performed leg curl exercise in a dorsiflexed position performed a higher total training volume.Highlights Different ankle positions (i.e. dorsiflexion or plantarflexion) do not affect hamstrings EMG activity during prone leg curl exercise.Different ankle positions show similar adaptation in strength and hypertrophy of biceps femoris long head after 10 weeks of training.Training in the plantarflexed position may be useful for time-constrained individuals, allowing similar training adaptations with smaller training volume.

The Pre-Exhaustion Method Does Not Increase Muscle Activity in Target Muscle During Strength Training in Untrained Individuals.

This study investigated the effects of the pre-exhaustion method on electromyographic activity (root mean square and median frequency) at different interval sets. Twenty adults with little or no experience in strength training performed the seated row exercise until muscular failure, with or without completing a previous pre-exhaustion set in a pullover exercise. Surface electrodes were placed over the latissimus dorsi, teres major, biceps brachii, and posterior deltoid muscles of the dominant side. The results showed no effect of pre-exhaustion on EMG activity of latissimus dorsi target muscle for any interval sets. Regarding median frequency, our results showed a consistent decrease throughout the sets (p>0.05). Also, our results revealed a decrease in posterior deltoid median frequency with pre-exhaustion (p=0.001). We conclude that the pre-exhaustion method seems ineffective in increasing the EMG activity of the desired muscle throughout all repetitions of strength training. Furthermore, pre-exhaustion seems to be a good way to increase fatigue in the posterior deltoid muscle.

Mind-Muscle Connection: Verbal Instructions Alter Electromyographic Activity for Elbow Flexors and Extensors During Co-Contraction Training.

Co-contraction training has demonstrated similar electromyographic (EMG) activity levels compared to conventional strength training. Since verbal instructions can increase EMG activity on target muscles during conventional exercises, the same should occur during co-contraction. In this study we analyzed whether different verbal instructions would alter the EMG activity of target muscles - biceps brachii (BB) and triceps brachii lateral head (TB) - during co-contraction training for the elbow joint. Seventeen males with experience in strength training performed a co-contraction set in two verbal instruction conditions to emphasize either elbow flexion or elbow extension. Surface electrodes were fixed over biceps brachii and triceps brachii lateral head muscles. We measured EMG mean amplitude and analyzed data with 2-way ANOVA. We found a significant interaction between muscle and verbal instruction (p = 0.002). Post hoc tests indicated that verbal instructions (p = 0.001) influenced the BB EMG activity (elbow flexion: M = 68.74, SD = 17.96%; elbow extension: M = 53.47, SD = 16.13%); and also showed difference (p = 0.006) in the EMG activity between BB and TB with verbal instruction emphasizing the elbow extension (BB: M = 53.47, SD = 16.13%; TB: M = 69.18, SD = 21.79%). There was a difference in the EMG ratio of BB/TB (p = 0.001) when focusing on elbow flexion (M = 1.09, SD = 0.30) versus elbow extension (M = 0.81, SD = 0.25). As verbal instruction modified the magnitude of muscle recruitment during co-contractions for elbow joint muscles, there is a clear mind-muscle connection of importance to this method of training. Also, of importance to trainers, verbal instructions seemed to affect individuals differentially.

Force stability training decreased force variability of plantar flexor muscles without reducing postural sway in female older adults.

BACKGROUND: Previous studies reported a relationship between postural sway and force variability of the plantar flexor muscles (PFM), such that less force variability related to lower postural sway; however, this association does not seem to exist in older adults. RESEARCH QUESTION: This study investigated the effect of force stability training of the PFM on force variability (FV) of these muscles and postural sway in female older adults. METHODS: Thirty female older adults were divided into three groups: TG5 (n = 10), who trained at 5% of maximum voluntary isometric contraction (MVIC) of the PFM; TG10 (n = 10), who trained at 10 % of MVIC of the PFM; and CG (n = 10) who did not perform any specific training for the PFM. Postural sway was evaluated during upright bipodal posture. Postural sway and FV of the PFM were assessed before and after the training period. Participants trained once a week for four weeks. RESULTS: After the training period, the FV decreased significantly for both TG5 (pre = 3.26 ± 0.83; post = 2.53 ± 0.60 N) and TG10 (pre = 3.50 ± 0.72; post = 2.85 ± 0.86 N), but the mean sway amplitude increased for both TG5 (pre = 0.017 ± 0.03; post = 0.19 ± 0.04 cm) and TG10 (pre = 0.14 ± 0.04; post = 0.16 ± 0.04 cm). SIGNIFICANCE: The force stability training decreased the FV of the PFM, but this decrease was insufficient to reduce postural sway in female older adults.

Mind-Muscle Connection: Limited Effect of Verbal Instructions on Muscle Activity in a Seated Row Exercise.

Verbal instruction increases electromyographic (EMG) activity in the first three repetitions of an exercise, but its effect on an entire exercise set until failure is unknown. Once there are changes in motor unit recruitment due to fatigue, the effect of verbal instructions can change during different intervals of a set. This study analyzed whether verbal instruction emphasized the contraction of back muscles (i.e., myoelectric activity) during initial, intermediate, and final exercise repetitions performed until failure. Twenty participants with little or no experience in strength training performed a seated row exercise with and without verbal instruction. Surface electrodes were fixed over the latissimus dorsi, teres major, biceps brachii, and posterior deltoid (PD) muscles. Myoelectric activity was computed by mean amplitude and by the median frequency. We analyzed data with repeated measures multivariate analysis of variance and found that, with verbal instruction, there was increased EMG mean amplitude in the latissimus dorsi (15.21%, p = .030) and reduced EMG mean amplitude in the PD (14.39%, p = .018) on initial repetitions. Other muscle EMG amplitudes did not change. On intermediate repetitions, there was reduced signal amplitude only in the PD (15.03%, p = .022). The verbal instruction did not interfere with signal amplitude on final repetitions nor in the median frequency throughout the series. Verbal instruction seems to have little effect on increasing myoelectric activity of these targeted muscles in an entire set of a resistance training.

The variability of the force produced by the plantar flexor muscles does not associate with postural sway in older adults during upright standing.

The force variability of the plantar flexor muscles (PFM) appears to be directly related to the control of upright standing. Nevertheless, this association is still uncertain in older adults. This study aimed to evaluate the relationship between PFM force variability and postural sway in the upright standing in older women. Forty older women performed submaximal plantar flexion movements measured by force transducers coupled to an experimental chair. They performed this task during three sets of 20 s at 5% and 10% of their maximum voluntary isometric contraction with and without the aid of visual feedback of the force produced. The volunteers then stood barefoot, with eyes closed and feet parallel on a force platform, which allowed the measurement of the center of pressure displacement in the anteroposterior direction. The results did not indicate a significant association between force variability of the PFMs and postural sway in older women. It can be inferred that the force variability of the PFM does not play an important role in controlling the posture in this population, suggesting that other factors may influence the functioning of the postural control system in older adults.

Training Level Does Not Affect Auditory Perception of The Magnitude of Ball Spin in Table Tennis.

Identifying the trajectory and spin of the ball with speed and accuracy is critical for good performance in table tennis. The aim of this study was to analyze the ability of table tennis players presenting different levels of training/experience to identify the magnitude of the ball spin from the sound produced when the racket hit the ball. Four types of "forehand" contact sounds were collected in the laboratory, defined as: Fast Spin (spinning ball forward at 140 r/s); Medium Spin (105 r/s); Slow Spin (84 r/s); and Flat Hit (less than 60 r/s). Thirty-four table tennis players of both sexes (24 men and 10 women) aged 18-40 years listened to the sounds and tried to identify the magnitude of the ball spin. The results revealed that in 50.9% of the cases the table tennis players were able to identify the ball spin and the observed number of correct answers (10.2) was significantly higher (χ2 = 270.4, p <0.05) than the number of correct answers that could occur by chance. On the other hand, the results did not show any relationship between the level of training/experience and auditory perception of the ball spin. This indicates that auditory information contributes to identification of the magnitude of the ball spin, however, it also reveals that, in table tennis, the level of training does not interfere with the auditory perception of the ball spin.

Analysis of postural control and muscular performance in young and elderly women in different age groups.

BACKGROUND: muscle strength and power are two factors affecting balance. The impact of muscle strength and power on postural control has not been fully explored among different age strata over sixty. OBJECTIVES: the aim of the present study was to assess the muscle strength and power of elderly women in different age groups and determine their correlation with postural control. METHOD: eighty women were divided into four groups: the young 18-30 age group (n=20); the 60-64 age group (n=20); the 65-69 age group (n=20); and the 70-74 age group (n=20). The participants underwent maximum strength (one repetition maximum or 1-RM) and muscle power tests to assess the knee extensor and flexor muscles at 40%, 70%, and 90% 1-RM intensity. The time required by participants to recover their balance after disturbing their base of support was also assessed. RESULTS: the elderly women in the 60-64, 65-69, and 70-74 age groups exhibited similar muscle strength, power, and postural control (p>0.05); however, these values were lower than those of the young group (p<0.05) as expected. There was a correlation between muscle strength and power and the postural control performance (p<0.05). CONCLUSION: despite the age difference, elderly women aged 60 to 74 years exhibited similar abilities to generate strength and power with their lower limbs, and this ability could be one factor that explains the similar postural control shown by these women.

The influence of vision and support base on balance during quiet standing in patients with adolescent idiopathic scoliosis before and after posterior spinal fusion.

BACKGROUND CONTEXT: Scoliosis is the most common postural alteration in adolescence and is characterized by deviations of the spine in three planes. Surgical treatment based on arthrodesis has been developed, but the effects of such restructuring on the systems involved in postural control need to be better understood. PURPOSE: To assess the influence of vision and the support base on balance in the quiet standing position in adolescents awaiting surgical treatment for idiopathic scoliosis. STUDY DESIGN/SETTING: Longitudinal study/Ribeirão Preto Clinics Hospital (HC-FMRP-USP) and Laboratory of Assessment and Rehabilitation of Equilibrium at the FMRP-USP. PATIENT SAMPLE: Adolescent idiopathic scoliosis patients and controls. OUTCOME MEASURES: Center of pressure (CoP) sway area of the 95% confidence ellipse. METHODS: Thirty female adolescents were divided into two groups according to their spinal alignment: control (n=15) and scoliosis groups (SGs) (n=15). The subjects with scoliosis were evaluated before and 7, 30, 60, and 90 days after surgery; the controls were evaluated once. The area of CoP oscillation was measured with the eyes open and closed and with two different support bases (feet apart or together). The force platform was purchased with funding support (US $8,375.00) provided by the Research Foundation of São Paulo (FAPESP). The study sponsors had no involvement in the study. Data were collected from the force platform and then statistically assessed through a linear model analysis of mixed effects. RESULTS: Data reveal that subjects in the SG oscillated more than controls, and postsurgery subjects had more oscillation than presurgery subjects. The results also indicated that both groups (control and scoliosis) showed more oscillation among those subjects with feet apart and eyes closed, but subjects with scoliosis were more affected by vision deprivation than by a reduced support base. CONCLUSIONS: Our results indicate that adolescents with idiopathic scoliosis are more dependent on visual information and that surgical correction does not change this relationship.

Analysis of postural control and muscular performance in young and elderly women in different age groups

BACKGROUND: muscle strength and power are two factors affecting balance. The impact of muscle strength and power on postural control has not been fully explored among different age strata over sixty. OBJECTIVES: the aim of the present study was to assess the muscle strength and power of elderly women in different age groups and determine their correlation with postural control. METHOD: eighty women were divided into four groups: the young 18-30 age group (n=20); the 60-64 age group (n=20); the 65-69 age group (n=20); and the 70-74 age group (n=20). The participants underwent maximum strength (one repetition maximum or 1-RM) and muscle power tests to assess the knee extensor and flexor muscles at 40%, 70%, and 90% 1-RM intensity. The time required by participants to recover their balance after disturbing their base of support was also assessed. RESULTS: the elderly women in the 60-64, 65-69, and 70-74 age groups exhibited similar muscle strength, power, and postural control (p>0.05); however, these values were lower than those of the young group (p<0.05) as expected. There was a correlation between muscle strength and power and the postural control performance (p<0.05). CONCLUSION: despite the age difference, elderly women aged 60 to 74 years exhibited similar abilities to generate strength and power with their lower limbs, and this ability could be one factor that explains the similar postural control shown by these women. .

Postural control in down syndrome: the use of somatosensory and visual information to attenuate body sway.

The purpose of this study was to examine the effects of visual and somatosensory information on body sway in individuals with Down syndrome (DS). Nine adults with DS (19-29 years old) and nine control subjects (CS) (19-29 years old) stood in the upright stance in four experimental conditions: no vision and no touch; vision and no touch; no vision and touch; and vision and touch. In the vision condition, participants looked at a target placed in front of them; in the no vision condition, participants wore a black cotton mask. In the touch condition, participants touched a stationary surface with their right index finger; in the no touch condition, participants kept their arms hanging alongside their bodies. A force plate was used to estimate center of pressure excursion for both anterior-posterior and medial-lateral directions. MANOVA revealed that both the individuals with DS and the control subjects used vision and touch to reduce overall body sway, although individuals with DS still oscillated more than did the CS. These results indicate that adults with DS are able to use sensory information to reduce body sway, and they demonstrate that there is no difference in sensory integration between the individuals with DS and the CS.