Effect of Reduced Feedback Frequencies on Motor Learning in a Postural Control Task in Young Adults.

The effects of the use of reduced feedback frequencies on motor learning remain controversial in the scientific literature. At present, there is still controversy about the guidance hypothesis, with some works supporting it and others contradicting it. To shed light on this topic, an experiment was conducted with four groups, each with different feedback frequencies (0%, 33%, 67%, and 100%), which were evaluated three times (pre-test, post-test, and retention) during a postural control task. In addition, we tested whether there was a transfer in performance to another similar task involving postural control. As a result, only the 67% feedback group showed an improvement in their task performance in the post-test and retention evaluations. Nevertheless, neither group showed differences in motor transfer performance compared to another postural control task. In conclusion, the findings of this paper corroborate the hypothesis of guidance and suggest that the use of a reduced frequency of 67% is a better option for improving motor learning than options that offer feedback at a lower frequency, at all trials or not at all.

Test-Retest Reliability of Task Performance for Golf Swings of Medium- to High-Handicap Players.

Background: Golf swing performance in medium- to high-handicap players must be reliably measured to use this variable in both research studies and in applied settings. Nevertheless, there are no studies published on this topic and test−retest evidence is only available for low-handicap players. The aim of this study was to determine the number of attempts necessary to obtain a reliable measurement protocol for swing performance variables in medium- to high-handicap players. Methods: Ten amateur players (55.67 (13.64) years, 78.4 (11.4) kg, 1.75 (7.95) m) took part in a test−retest study in two experimental sessions one week apart. In each one, fifteen swings with a six iron and a driver were evaluated with a 3D Doppler tracking golf radar. Results: The results showed that variables related to side carry could not be reliably measured in medium- to high-handicap players in only fifteen trials (ICC < 0.26, SEM > 12.05 m and MDC > 33.41 m). The rest of the performance variables related to the club and ball trajectories could be reliably measured with a 3D Doppler radar with between seven and ten swings. Conclusions: At least seven swings are recommended for the driver and ten for the six iron to measure golf swing performance.

The Relevance of Dual Tasking for Improving Trunk Muscle Endurance After Back Surgery.

OBJECTIVE: To determine the effect of dual tasking on trunk muscle endurance in patients after lumbar diskectomy. DESIGN: Cross-sectional study. SETTING: Rehabilitation hospital setting. PARTICIPANTS: Individuals (N=14) undergoing primary lumbar diskectomy. INTERVENTION: Using a randomized design on 2 separate days, muscle endurance was evaluated during prone bridging and Biering-Sorensen tests. Each test was randomly performed under 2 cognitive conditions: single task without cognitive condition and self-regulated dual task (ie, mathematical task). MAIN OUTCOME MEASURES: The primary outcomes were time to failure and pain assessed by the visual analog scale from 0 to 100 mm. The secondary outcomes were kinesiophobia assessed by the Tampa Scale and disability assessed by the Oswestry Disability Index. Associations were tested using a repeated measures analysis of variance with relevant interaction test. RESULTS: A significant interaction between condition, endurance tests, and kinesiophobia (P=.005) was found. The post hoc comparison showed positive effects between cognitive conditions in both endurance tests (prone bridging test: mean difference, 15.7s; 95% confidence interval [CI], 7.5-24s; P=.001; Biering-Sorensen test: mean difference, 7.9s; 95% CI, 1.9-14s; P=.014). The linear regression analysis between the Tampa Scale for Kinesiophobia and the difference of time to failure between cognitive conditions showed a positive correlation only during the Biering-Sorensen test (r=0.80; P=.001). CONCLUSIONS: A self-regulated dual task increases trunk muscle endurance in patients after lumbar diskectomy. The results suggest that the difference observed in time to failure between the single task and dual task is associated with fear avoidance, especially during back extension. This strategy seems especially relevant for patients with high levels of fear avoidance and may be used to improve trunk muscle endurance.

Profiling children longitudinally: A three-year follow-up study of perceived and actual motor competence and physical fitness.

Longitudinal designs enhance our understanding of children's development and its influence on movement behaviors and health. This three-year follow-up study aimed to develop profiles according to perceived and actual motor competence (MC) (locomotion, object control, and overall) and physical fitness in boys and girls longitudinally including children's temporal migrations among clusters in terms of profiling trends. A secondary aim was to compare physical activity participation and weight status at each time point according to these profiles. One hundred and four typically developing Spanish children (45.8% girls) between 4 and 9 years old at baseline participated in this study. Data were collected at three time points one year apart, between January 2016 and May 2018. A self-organizing map and K-means cluster analysis were used to classify and visualize the values and temporal trajectories longitudinally. The study of the profiles in three consecutive years revealed five profiles, three for boys [ie, profile 1 (aligned-high), profile 2 (aligned-partially-low perception-medium actual MC and fitness), and profile 3 (non-aligned-medium perception-low actual MC and fitness)]; and two for girls [ie, profile 4 (aligned-high) and profile 5 (aligned-low)]. For highly perceived and capable children, boys (profile 1) and girls (profile 4), there was a tendency for higher physical activity participation and lower body mass index and waist circumference over time compared to their counterparts who had medium and/or low levels in perception and actual MC and fitness (P < .05). As children age, those with low values in perceived and actual MC and fitness in object control skills will present a higher probability of maintaining unhealthy lifestyles. So, prior intervention, children's profiles identification should be analyzed according to the type of MC.

Perceived movement skill competence in stability: Validity and reliability of a pictorial scale in early adolescents.

Perceived motor competence (PMC) is important to health as it mediates the association between actual motor competence (AMC) and physical activity. Many instruments assess the broader construct of physical self-perception but no scale has been developed to assess PMC in stability. The aim of this study was to develop and analyze the reliability and validity of a new pictorial PMC in stability skill assessment when completed by early adolescents. A Delphi method showed ≥70% of experts' consensus in the seven proposed items. A sample of 904 students (11-14 years old) self-reported PMC in locomotion, object control, and stability using two pictorial scales: Perceived Movement Skill Competence (PMSC) and the newly developed Stability (PMSC_Stability). The Körperkoordinations test for Kinder (KTK) was also administered as a measure of AMC in skills that utilize stability. Two different subsamples were randomly assigned to criterion validity and reliability assessments. Spearman's correlation, confirmatory factor analysis, and a general linear model for sex and age were conducted. The internal consistency (α) and test-retest (intraclass correlation coefficient) reliability values were good (>0.70). A single-factor latent model represented stability and did not differ by sex. Stability perception was associated with AMC (rho = 0.51). Stability is important to the performance of many movement skills (eg, single-leg balance or moving on a narrow surface). Understanding which adolescents have poor stability perception could highlight stability as an area that needs targeting in order to increase physical activity and sport participation.

Validation of Using Smartphone Built-In Accelerometers to Estimate the Active Energy Expenditures of Full-Time Manual Wheelchair Users with Spinal Cord Injury.

This study aimed to investigate the validity of using built-in smartphone accelerometers to estimate the active energy expenditures of full-time manual wheelchair users with spinal cord injury (SCI). Twenty participants with complete SCI completed 10 5-min daily activities that involved the upper limbs, during which their oxygen consumption and upper limb activity were registered using a portable gas analyzer and a smartphone (placed on the non-dominant arm), respectively. Time series of 1-min averaged oxygen consumption and 55 accelerometer variables (13 variables for each of the four axes and three additional variables for the correlations between axes) were used to estimate three multiple linear models, using a 10-fold cross-validation method. The results showed that models that included either all variables and models or that only included the linear variables showed comparable performance, with a correlation of 0.72. Slightly worse general performance was demonstrated by the model that only included non-linear variables, although it proved to be more accurate at estimating the energy expenditures (EE) during specific tasks. These results suggest that smartphones could be a promising low-cost alternative to laboratory-grade accelerometers to estimate the energy expenditure of wheelchair users with spinal cord injury during daily activities.

Different neighborhood walkability indexes for active commuting to school are necessary for urban and rural children and adolescents.

BACKGROUND: Literature focusing on youth has reported limited evidence and non-conclusive associations between neighborhood walkability measures and active commuting to and from school (ACS). Moreover, there is a lack of studies evaluating both macro- and micro-scale environmental factors of the neighborhood when ACS is analyzed. Likewise, most studies on built environment attributes and ACS focus on urban areas, whereas there is a lack of studies analyzing rural residential locations. Moreover, the relationship between built environment attributes and ACS may differ in children and adolescents. Hence, this study aimed to develop walkability indexes in relation to ACS for urban and rural children and adolescents, including both macro- and micro-scale school-neighborhood factors. METHODS: A cross-sectional study of 4593 participants from Spain with a mean age of 12.2 (SD 3.6) years was carried out. Macro-scale environmental factors were evaluated using geographic information system data, and micro-scale factors were measured using observational procedures. Socio-demographic characteristics and ACS were assessed with a questionnaire. Several linear regression models were conducted, including all the possible combinations of six or less built environment factors in order to find the best walkability index. RESULTS: Analyses showed that intersection density, number of four-way intersections, and residential density were positively related to ACS in urban participants, but negatively in rural participants. In rural children, positive streetscape characteristics, number of regulated crossings, traffic calming features, traffic lanes, and parking street buffers were also negatively related to ACS. In urban participants, other different factors were positively related to ACS: number of regulated crossings, positive streetscape characteristics, or crossing quality. Land use mix acted as a positive predictor only in urban adolescents. Distance to the school was a negative predictor on all the walkability indexes. However, aesthetic and social characteristics were not included in any of the indexes. CONCLUSIONS: Interventions focusing on improving built environments to increase ACS behavior need to have a better understanding of the walkability components that are specifically relevant to urban or rural samples.

Effects of dual-task demands on the complexity and task performance of submaximal isometric handgrip force control.

PURPOSE: To determine the effect of cognitive-motor dual-task load on temporal structure irregularity (complexity) of motor output and task performance of submaximal isometric contractions. METHODS: Twelve young, sedentary subjects performed handgrip isometric contractions until failure at 50% of maximal voluntary contraction under mathematical self-regulated dual-task (own pace; SDT), regulated dual-task (imposed pace; RDT), and control. Force signal complexity was calculated by sample entropy at the initial, middle, and final thirds. Task performance was assessed by muscle fatigue (time to failure and rate of median frequency of the radial flexor of the carpus), force and math task error, and self-perceived difficulty. RESULTS: Only RDT decreased complexity with respect to control (17.4% ± 12.6%, p = 0.005), all conditions decreased complexity by the final third (Control: 52.8% ± 18.7%, p < 0.001; SDT: 41.1% ± 32.1%, p = 0.003; RDT: 19.1% ± 21.9%, p = 0.035). Conditions did not affect time to failure, and only RDT decreased the rate of median frequency (0.1%/s ± 0.1%/s, p = 0.020). Inferior force error rate was increased by conditions (SDT: 1.5% ± 0.8%, p < 0.001; RDT: 2% ± 1.5%, p = 0.002). Math error was only augmented by RDT (from 9.9 ± 6.7 to 51.7 ± 18.8, p < 0.001), categorized as "very hard" in 85.7% of participants (p = 0.015). CONCLUSION: Only the RDT condition reduced complexity and neuromuscular fatigue while increasing force error rate of the handgrip's motor output, without affecting time to failure. A highly demanding dual-task may become a strategy to modify the organization of the hand force motor output, which may contribute to its motor adaptations.

Profiling movement behaviours in pre-school children: A self-organised map approach.

Application of machine learning techniques has the potential to yield unseen insights into movement and permits visualisation of complex behaviours and tangible profiles. The aim of this study was to identify profiles of relative motor competence (MC) and movement behaviours in pre-school children using novel analytics. One-hundred and twenty-five children (4.3 ± 0.5y, 1.04 ± 0.05 m, 17.8 ± 3.2 kg, BMI: 16.2 ± 1.9 kg.m2) took part in this study. Measures included accelerometer-derived 24-h activity, MC (Movement Assessment Battery for Children second edition), height, weight and waist circumference, from which zBMI were derived. Self-Organised Map (SOM) analysis was used to classify participants' profiles and a k-means cluster analysis was used to classify the neurons into larger groups according to the input variables. These clusters were used to describe the individuals' characteristics according to their MC and PA compositions. The SOM analysis indicated five profiles according to MC and PA. One cluster was identified as having both the lowest MC and MVPA (profile 2), whilst profiles 4 and 5 show moderate-high values of PA and MC. We present a novel pathway to profiling complex tenets of human movement and behaviour, which has never previously been implemented in pre-school children, highlighting that the focus should change from obesity monitoring, to "moving well".Abbreviations: MC: Motor competence; PA: Physical activity; MVPA: Moderate-to-vigorous physical activity; SOM: Self-organized map; BMI: Body mass index; MABC2: Movement assessment battery for children 2nd edition; MANOVA: Multiple analysis of variance.

Impact of Visual Biofeedback of Trunk Sway Smoothness on Motor Learning during Unipedal Stance.

The assessment of trunk sway smoothness using an accelerometer sensor embedded in a smartphone could be a biomarker for tracking motor learning. This study aimed to determine the reliability of trunk sway smoothness and the effect of visual biofeedback of sway smoothness on motor learning in healthy people during unipedal stance training using an iPhone 5 measurement system. In the first experiment, trunk sway smoothness in the reliability group (n = 11) was assessed on two days, separated by one week. In the second, the biofeedback group (n = 12) and no-biofeedback group (n = 12) were compared during 7 days of unipedal stance test training and one more day of retention (without biofeedback). The intraclass correlation coefficient score 0.98 (0.93-0.99) showed that this method has excellent test-retest reliability. Based on the power law of practice, the biofeedback group showed greater improvement during training days (p = 0.003). Two-way mixed analysis of variance indicates a significant difference between groups (p < 0.001) and between days (p < 0.001), as well as significant interaction (p < 0.001). Post hoc analysis shows better performance in the biofeedback group from training days 2 and 7, as well as on the retention day (p < 0.001). Motor learning objectification through visual biofeedback of trunk sway smoothness enhances postural control learning and is useful and reliable for assessing motor learning.

Identifying profiles of children at risk of being less physically active: an exploratory study using a self-organised map approach for motor competence.

This study aims to develop profiles in children according to physical fitness, actual and perceived motor competence, and to examine the level of engagement in physical activity and weight status according to these profiles. In the study, 156 typically developing Spanish children (47.4% girls) of primary school age (5-11 years-old) participated voluntarily. Children's perceived and actual motor competence, physical fitness, physical activity participation and weight status were assessed. A Self-Organising Map and K-means cluster analysis were used to classify and visualise the values. Four profiles were found: profile 2 was aligned - high capacity, high perception, profile 1 was partially aligned - medium capacity and perception, profile 3 and 4 were both non-aligned - low capacity, medium perception and medium capacity, low perception; respectively. Children in profile 2 were more active than children in profile 3 and 4 (P < .05). In profile 2 there was a lower frequency of overweight/obese children than normal-weight children. On the contrary, in profiles 1, 3 and 4 a similar distribution of normal-weight and overweight/obese children was found. High capable children with high perception exhibited higher physical activity participation and were more likely to be of normal-weight compared to those with low capacity and/or perception.

Ski Boots Do Not Impair Standing Balance by Restricting Ankle-Joint Mobility.

OBJECTIVE: This study was undertaken in order to provide new insight into sensorimotor control of posture when wearing high-shaft (HS) boots as ski boots. BACKGROUND: Previous studies into the effects of HS boots on postural control have produced controversial results. Some studies reported postural control impairments with ski boots in bipedal postural tasks due to ankle movement restrictions without quantifying the actual restrictive effect of these boots and specifying the adaptations of the postural control system. METHOD: Eighteen young healthy subjects took part in the experiment. Bilateral postural control was assessed on stable and unstable surfaces, while standing barefoot or wearing ski boots. Center of pressure (COP) parameters, ankle, knee, and hip joints movements were calculated and EMG activity from main postural muscles was recorded. RESULTS: Ski boots did not restrict the amplitude of ankle angular movements and largely impacted COP parameters and EMG activity on stable ground. In conditions of mediolateral instability, COP data illustrated an enhanced postural control in the frontal plane when wearing ski boots. CONCLUSIONS: Ski boots do not affect bipedal postural balance by restricting the ankle angular motions but induce complex adaptations of the postural control system which combine factors of a mechanical, motor, and sensorial nature. They impede postural control mainly when standing on stable ground without producing similar deleterious effects on unstable surfaces. APPLICATION: Our results show that HS boots as ski boots can improve lateral balance on unstable surfaces, which can contribute to prevent fall risk and ankle sprain.

Fatigue does not conjointly alter postural and cognitive performance when standing in a shooting position under dual-task conditions.

This study investigated the effects of fatigue on balance control and cognitive performance in a standing shooting position. Nineteen soldiers were asked to stand while holding a rifle (single task - ST). They also had to perform this postural task while simultaneously completing a cognitive task (dual task - DT). Both the ST and DT were performed in pre- and post-fatigue conditions. In pre-fatigue, participants achieved better balance control in the DT than in the ST, thus suggesting that the increased cognitive activity associated with the DT improves balance control by shifting the attentional focus away from a highly automatised activity. In post-fatigue, balance control was degraded in both the ST and DT, while reaction time was enhanced in the first minutes following the fatiguing exercise without affecting the accuracy of response in the cognitive task, which highlights the relative independent effects of fatigue on balance control and cognitive performance.

The difficulty of postural tasks amplifies the effects of fatigue on postural stability.

PURPOSE: It was supposed that the difficulty of postural tasks accentuates the effects of fatigue on postural stability. The aim of this work was to compare the effects of fatiguing running on three different postural conditions presenting different levels of difficulty: a standing still position with the eyes open (EO condition), a standing still position with the eyes closed (EC condition) and a shooting position with the eyes open (SP condition). The SP condition required a rifle to be held horizontally with the arms and a standing posture with the non-dominant foot ahead of the dominant foot. METHODS: Thirty-two male soldiers 32.2 ± 3.8 years old completed a maximal incremental protocol on a treadmill by running until they reached a state of fatigue. The three postural conditions were evaluated in a randomized order before and after the fatiguing exercise with the use of a force platform which recorded the displacements of the centre of foot pressure. RESULTS: Following the fatiguing running exercise, postural stability was affected to a greater extent in the SP condition than in the EO condition and the EC condition. CONCLUSION: The requirements of the SP condition modify the entire postural organization and this challenges balance control to a greater extent than when in EO and EC standing still positions, following fatiguing exercise. The difficulty of postural tasks thus amplifies the effects of fatigue on postural stability.

Physical activity, physical fitness and academic achievement in adolescents: a self-organizing maps approach.

The relationship among physical activity, physical fitness and academic achievement in adolescents has been widely studied; however, controversy concerning this topic persists. The methods used thus far to analyse the relationship between these variables have included mostly traditional lineal analysis according to the available literature. The aim of this study was to perform a visual analysis of this relationship with self-organizing maps and to monitor the subject's evolution during the 4 years of secondary school. Four hundred and forty-four students participated in the study. The physical activity and physical fitness of the participants were measured, and the participants' grade point averages were obtained from the five participant institutions. Four main clusters representing two primary student profiles with few differences between boys and girls were observed. The clustering demonstrated that students with higher energy expenditure and better physical fitness exhibited lower body mass index (BMI) and higher academic performance, whereas those adolescents with lower energy expenditure exhibited worse physical fitness, higher BMI and lower academic performance. With respect to the evolution of the students during the 4 years, ∼25% of the students originally clustered in a negative profile moved to a positive profile, and there was no movement in the opposite direction.

POSTURAL CONTROL MECHANISMS IN HEALTHY ADULTS IN SITTING AND STANDING POSITIONS.

This study explored differences in the center of pressure in healthy people in a sitting and standing position and with eyes open and closed. With this purpose, 32 healthy participants (16 men, 16 women; M age=25.2 yr., SD=10.0, range=18-55) were measured with an extensiometric force plate. Using a two-way repeated-measures multivariate analysis of variance (MANOVA), the root mean square, velocity, range, and sway, in both visual conditions, had higher values in the standing task than in the sitting task. In the frequency domain, the low-frequency band had higher values during the standing task. For control mechanism variables, mean distance and time were greater when standing while mean peaks were greater when sitting. Thus, stability is worse in the standing position and more neuromuscular activity is required to maintain balance.

Use of heart rate variability in monitoring stress and recovery in judo athletes.

The main objective of this study was to examine the effect of different judo training loads on heart rate variability (HRV) measurements, to determine if they can be used as valid indicators in monitoring stress and recovery in judo athletes. Fourteen male national-standard judo athletes were randomly divided into 2 groups, and each group followed a different type of training, namely, a high training load (HTL) and a moderate training load program (MTL). Data collection included HRV measurements, a Recovery Stress Questionnaire for athletes (RESTQ-SPORT), and strength measurements, 4 weeks before and after the training program. The HTL group had lower square root of the mean squared difference of successive RR intervals, very low frequency, high frequency, short-term variability, short-range scaling exponents, general recovery, sport-specific recovery, general stress, maximum strength, maximum power, and higher low/high frequency ratio at posttest compared with pretest (p ≤ 0.05). The HTL group showed lower short-range and long-range scaling exponents, general recovery, sport-specific recovery, and higher general stress than the MTL group in posttest measurements (p ≤ 0.05). In conclusion, judo athletes enrolled in an HTL program showed an imbalance of the autonomic nervous system with decreased vagal modulation, together with a decrease in strength parameters, higher markers for stress, and a lower perception of recovery.

Construct and concurrent validation of a new resistance intensity scale for exercise with thera-band® elastic bands.

The construct and concurrent validity of the Thera-Band Perceived Exertion Scale for Resistance Exercise with elastic bands (EB) was examined. Twenty subjects performed two separate sets of 15 repetitions of both frontal and lateral raise exercise over two sessions. The criterion variables were myoelectric activity and heart rate. One set was performed with an elastic band grip width that permitted 15 maximum repetitions in the selected exercise, and another set was performed with a grip width 50% more than the 15RM grip. Following the final repetition of each set, active muscle (AM) and overall body (O) ratings of perceived exertion (RPE) were collected from the Thera-Band® resistance exercise scale and the OMNI-Resistance Exercise Scale of perceived exertion with Thera-Band® resistance bands (OMNI-RES EB). Construct validity was established by correlating the RPE from the OMNI-RES EB with the Thera-Band RPE scale using regression analysis. The results showed significant differences (p ≤ 0.05) in myoelectric activity, heart rate, and RPE scores between the low- and high-intensity sets. The intraclass correlation coefficient for active muscles and overall RPE scale scores was 0.67 and 0.58, respectively. There was a positive linear relationship between the RPE from the OMNI-RES EB and the Thera-Band scale. Validity coefficients for the RPE AM were r(2) = 0.87 and ranged from r(2) = 0.76 to 0.85 for the RPE O. Therefore, the Thera-Band Perceived Exertion Scale for Resistance Exercise can be used for monitoring elastic band exercise intensity. This would allow the training dosage to be better controlled within and between sessions. Moreover, the construct and concurrent validity indicates that the OMNI-RES EB measures similar properties of exertion as the Thera-Band RPE scale during elastic resistance exercise. Key pointsThis new resistance intensity scale is an appropriate and valid tool for assessing perceived exertion during strength training with elastic bands.This scale can be used without reducing the accuracy of the dosage prescribed during training/rehabilitation sessions and while carrying out medium and/or long-term periodization programs or therapeutic interventions.Populations with specific physical or physiological needs could have access to an easy-to-use resource that allows them to carry out their training/rehabilitation programs with greater efficacy and without any risk to health.

Test-retest reliability of putting-related variables in medium-to-high handicap golf players.

This manuscript aims to study the reliability of different variables related to performance and acceleration during the golf putt in players with medium-to-high handicaps and to determine the number of attempts necessary to find reliable values for these variables. Eight males and two females [55.67 (13.64) years, 78.4 (11.4) kg, 1.75 (7.95) m] participated in two experimental sessions separated by one week. In these sessions, they performed three blocks of 10 putts trying to stop the golf ball at the center of a dartboard painted 2 m away. The performance was assessed depending on the area of the dartboard where the ball stopped, and the acceleration signals were acquired using the Xsens Dot. The results showed that to evaluate performance, 18 trials were necessary to reach reliable values using the 0-10 scoring system, and 28 trials were necessary for the 0-3 scoring system. Regarding the reliability of the accelerometer-related variables, 7 attempts were necessary to obtain good-to-excellent reliability values for most of the variables. It could be concluded that putting in medium-to-high handicap golf players can be reliably measured using the abovementioned protocol.

Detection of intermuscular coordination based on the causality of empirical mode decomposition.

Considering the stochastic nature of electromyographic (EMG) signals, nonlinear methods may be a more accurate approach to study intermuscular coordination than the linear approach. The aims of this study were to assess the coordination between two ankle plantar flexors using EMG by applying the causal decomposition approach and assessing whether the intermuscular coordination is affected by the slope of the treadmill. The medial gastrocnemius (MG) and soleus muscles (SOL) were analyzed during the treadmill walking at inclinations of 0°, 5°, and 10°. The coordination was evaluated using ensemble empirical mode decomposition, and the causal interaction was encoded by the instantaneous phase dependence of time series bi-directional causality. To estimate the mutual predictability between MG and SOL, the cross-approximate entropy (XApEn) was assessed. The maximal causal interaction was observed between 40 and 75 Hz independent of inclination. XApEn showed a significant decrease between 0° and 5° (p = 0.028), between 5° and 10° (p = 0.038), and between 0° and 10° (p = 0.014), indicating an increase in coordination. Thus, causal decomposition is an appropriate methodology to study intermuscular coordination. These results indicate that the variation of loading through the change in treadmill inclination increases the interaction of the shared input between MG and SOL, suggesting increased intermuscular coordination.