Brazilian Journal of Motor Behavior

Individual Control Strategies in Training: Myoelectric activity and recruitment strategies in the co-contraction training

Nilson R. S. Silva — 2023-09-30

BACKGROUND: The literature in motor control has abundant evidence on within-/between-person variability when it comes to control strategies in several behaviors - which largely influences intervention outcomes. Despite being an intervention itself, strength training paradigms are yet to be analyzed beyond the average behavior. Based on myoelectric activity (EMG) analyses, this study emerges as a descriptive analysis on how the co-contraction training paradigm provides stimuli for strength training of knee extensors and flexors.

AIM: Considering the potential large interindividual variability in muscle activation patterns during resistance training, we explored the co-contraction paradigm considering the individual characteristics.

METHOD: Ten active male adults participated in two days of co-contraction training paradigm with their EMG activity collected (sartorius, biceps femoris long and short heads, semitendinosus, semimembranosus, rectus femoris, vastus lateralis and medialis and tensor fascia-latae).

RESULTS: On average, participants recruit 36% of their maximum EMG amplitude, decay 0.41% per repetition but increase 7.45% between sessions. The training stimulated similarly the knee flexors and extensors EMG ratio of all participants. However, participants demonstrated different average muscle recruitment patterns with few individuals modifying, largely, their recruitment over repetitions/days. Between and within-variability in recruitment pattern was maintained throughout repetitions and days.

CONCLUSION: Thus, the co-contraction training demonstrated sufficient muscle activation to be employed and evoked similar muscular recruitment between agonists and antagonists. To the best of our knowledge, this is a pioneer study encompassing the complexity of movement control in evaluating a strength training protocol.

Fascicle shortening upon activation in voluntary human muscle contractions

Heiliane de Brito Fontana — 2023-09-30

BACKGROUND: The dependence of fascicle length on complex interactions with joint angle and force challenges the interpretation of in vivo joint mechanics, muscle mechanical properties, contractile behavior, and muscle function.

AIM: The purpose of this study was to determine the complex interaction between muscle activation, joint angle, and fascicle length for isometric contractions of the human vastus lateralis muscle (VL).

METHOD: Knee extensor torques, joint angles, EMG activation, and fascicle lengths were determined in nine healthy subjects during maximal and submaximal isometric contractions.

RESULTS: Fascicle shortening during isometric contractions depended on muscle-tendon unit length/joint angle and activation, reaching a maximum between angles where VL had its maximum force potential and minimum resistance to fascicle shortening. Maximal fascicle shortening shifted to shorter muscle-tendon unit lengths with decreasing activation.

CONCLUSION: Fascicle shortening upon activation depends crucially on the force generating potential and stiffness of the muscle and can reach 30% of the resting fascicle length. Not accounting for the complex interactions between muscle length, force potential, muscle structure, and muscle stiffness has led to erroneous interpretations of the function and properties of healthy and diseased muscles.

Different levels of physical activity and postural balance in women with multiple sclerosis

Eduarda F. A. Machado — 2023-09-30

BACKGROUND:Multiple Sclerosis (MS) presents some clinical manifestations that may indicate motor, sensory and cognitive dysfunctions. Motor dysfunctions in MS are related to balance impairment, muscle weakness, gait, and fatigue and can lead to a significant decrease in quality of life. Postural balance is crucial for daily life activities and can be assessed by posturography.

AIM:The primary objective was to evaluate the influence of different levels of habitual physical activity (PA) on postural balance in women with MS. Additionally, we included an evaluation of walking, mobility, fatigue, and quality of life.

METHOD:This is a cross-sectional study with 25 women with MS. Habitual PA was measured using the Baecke-Questionnaire, separated into low-level (LL) and high-level (HL) PA. Posturography was used to evaluate postural balance and obtain displacement of the center of pressure (CoP-speed, CoP-area). We evaluated gait spatiotemporal-parameters (GAITRite), walking performance (6MWT), functional mobility (TUG), fatigue (FSS, MFIS), and quality-of-life (FAMS).

RESULTS:The difference in CoP-speed and CoP-area was significant (p<0.05) with LL group presented greater values than the HL group. We found a medium effect size CoP-speed (Cohen’s d=0.6) and higher CoP-area (Cohen’s d=1.1). No significant differences with the other variables were found.

CONCLUSION:The results showed that the group with a LL PA presented worse postural balance compared to the group HL. Although level of PA and balance seem to be related, the results of this cross-sectional study could not confirm a causal inference. It is important to develop different strategies to increase PA levels and posture balance in women with MS.

Study of cerebral cortico-cortical coherence during motor practice

Tércio Apolinário-Souza — 2023-09-30

BACKGROUND: Coherence is one of the neural mechanisms related to communication and plasticity. The literature presents two divergent results regarding coherence and motor practice. One result suggests a decrease in coherence during practice, while the other indicates an increase in coherence throughout practice.

AIM: Considering these two divergent results in the literature, this study aimed to examine the role of coherence in motor practice. We hypothesize that electrode pairs related to C3 (C3-P3 and C3-F3) show an increase of coherence during practice, while electrodes less related to motor action (F4, C4, and P4) may exhibit decreased.

METHOD: Twenty-four right-handed participants practice 120 trials of a sequential key-pressing task.

RESULTS: The results indicated, in the alpha upper and theta bands, from initiation to end of practice, the coherence increased in the F3-C3 electrode pair and decreased in the C3-C4, C3-P3, P3-P4, F3-P3, and C4-P4 electrodes pairs.

CONCLUSION: The results partially confirmed the hypothesis. The coherence increases in the electrode pairings related to the motor execution and decreases between the lesser related. During the motor learning process, communication reduction occurred in groups of neurons not associated with the stimulus, and the potentiation of synaptic plasticity within groups of neurons associated with the stimulus occurred.

Is the rate of force development scaling factor associated with the rate of agonist muscle activation scaling factor and the level of agonist-antagonist coactivation?

Hebberty M. Saavedra-Barbosa — 2023-09-30

BACKGROUND: Rate of force development scaling factor (RFD-SF) is used to assess neuromuscular quickness across submaximal levels. It has been suggested that such metric would be associated with the magnitude of the agonist muscle activation and with the level of simultaneous antagonist muscle group activation, i.e., agonist-antagonist coactivation.

AIM: To examine the associations between 1) the RFD-SF and the rate of agonist muscle activation scaling factor (RAgMA-SF) and 2) the RFD-SF and the agonist-antagonist coactivation.

METHOD: Eleven healthy and physically active subjects (7 men and 4 women, aged between 18 and 22 years) performed maximal strength tests of the knee extensors and flexors and a test that involved the production of brief submaximal force pulses of the knee extensors. The force exerted was recorded by a load cell and the electromyographic activities of the vastus lateralis and biceps femoris muscles were obtained during the tests. In the brief force pulses test, individuals were asked to produce around 120 submaximal force pulses that ranged between 20 to 80% of their maximum force value, while trying to produce each force pulse as fast as possible. The values of RFD-SF, RAgMA-SF of the vastus lateralis muscle, and a coactivation index (I_COA) were computed.

RESULTS: The RFD-SF is strongly associated with the RAgMA-SF (r=0.74; p=0.009) but not with the I_COA (r=0.29; p=0.38).

CONCLUSION: The RFD-SF is directly associated with the rate of agonist muscle activation and is not affected by the degree of coactivation between agonist and antagonist muscles.

Effects of anxiety, visual target predictability and pain on gaze behavior during a visuomotor task

Maysa P. G. Leopoldo — 2023-09-30

BACKGROUND: Attention and cognitive effort during postural control can be influenced by under threatening situations, such as pain, particularly in anxious individuals when visually tracking a target.

AIM: This study aimed to investigate the effects of anxiety, visual target type, and acute lumbar muscle pain on gaze behavior during a visual pursuit/postural control task.

METHOD: Nine young adult participants underwent testing over three time periods: (1) pre-infusion, (2) intramuscular (multifidus muscles) infusion of hypertonic (acute pain)/isotonic (placebo) solution, and (3) post-infusion (after 40 minutes after pain is vanished). The two sessions were separated by one week, in a counterbalanced order. During each session, participants performed a postural control task with visual pursuit, focusing on three targets (fixed, stochastic, and deterministic - 3 trials per target) while wearing an eye-tracker. STAI/IDATE was used to assess the participants' level of state anxiety: n=4 high-anxious and n=5 low-anxious. Continuous time of gaze on target (CTGT) and pupil diameter variability (PDV) were grouped into blocks of 3 trials.

RESULTS: High-anxious participants exhibited greater variability in PDV during the infusion period. The deterministic target required less visual attention (shorter CTGT) compared to the fixed and stochastic targets. Both injected solutions (hypertonic and isotonic) had similar effects on CTGT and PDV.

CONCLUSION: During the postural control task with visual pursuit: (1) high-anxious participants exerted greater cognitive effort, (2) participants deflected visual attention on the deterministic target, (3) acute and placebo muscle pain did not affect visual attention and cognitive effort.

Michael Turvey: A Legacy of Scientific Excellence and Kindness

Vitor L. S. Profeta — 2023-09-30

Michael Turvey’s research in motor control and coordination influenced many generations of movement scientists, Brazilian scholars included. Throughout his career, Michael Turvey aimed for excellence in research, teaching, and mentoring while treating students and colleagues with kindness.

Infographic: Developmental Coordination Disorder (Part II) – Recommendations for Motor Interventions

Priscila Tamplain — 2023-09-30

Children with Developmental Coordination Disorder (DCD) have motor coordination below expectations for their chronologic age and are commonly described as clumsy¹. The goal of this infographic is to provide information on recommendations for motor intervention of DCD based on information available on a recent study². Overall, the literature affirms that children with a diagnosis of DCD should receive intervention. Both physical and occupational therapy are recommended and can help children perform everyday tasks. According to the international clinical practice guidelines³, when planning a program of intervention, it is recommended that both the strengths and weaknesses of the individual in their environmental context should be taken into account in order to improve motor function, activity, and participation.

Smits-Engelsman and colleagues² classified motor interventions with basis on the International Classification of Functioning (ICF) framework: 1) body function and structure (BF) oriented, where the activity engaged in is designed to improve targeted body functions considered to underlie the reported functional motor problem; 2) activity oriented where the activity engaged in is designed to improve performance in that activity; and 3) participation oriented, where the activity engaged in is designed to improve participation in that activity in an everyday life situation. Overall, positive benefits were evident for activity-oriented approaches, body function-oriented when combined with activities, active video games, and small group programs². However, the authors explained the need for more rigorous RCTs with follow-up to demonstrate sustained change rather than just short-term gains in performance.

A specific approach that shows overall effectiveness is the Cognitive Orientation to daily Occupational Performance (CO-OP), which is an individualized, task-specific (activity-oriented), cognitive-based, problem-solving approach for individuals experiencing difficulties performing the skills they want or need to do. A recent randomized waitlist-control trial showed that CO-OP was effective in achieving and maintaining functional motor goals after 3 months for children with DCD⁴.

Other specific recommendations involve the incorporation of physical fitness (cardiorespiratory fitness and functional strength) protocols, Neuromotor Task Training (NTT), and the use of motor imagery training³. The severity of motor impairment affects not only the presentation of DCD but also participation, which has important implications for treatment³. Different interventions may be required at key stages of development or periods of transition to target participation⁵. Overall, it is recommended that individuals with DCD are given ample opportunity to practice movement skills to learn them and to participate in daily activities (e.g., at home, school, in community and leisure settings, and in sports).

Editorial: Fatigue Role in Modulating Motor Skills and Muscular Responses

Bruno L. S. Bedo — 2023-09-30

This editorial beckons readers to the intricate relationship between fatigue and motor control skills. This theme is explored in the ensuing special issue through the lens of esteemed researchers in the field. The articles within this issue provide a comprehensive and insightful analysis of how fatigue acts as a silent saboteur, subtly undermining the efficiency and efficacy of motor responses and skills. Through a tapestry of carefully conducted studies and thought-provoking findings, contributors shed light on how fatigue insidiously affects neuromuscular responses, from altering muscle activation during specific tasks to influencing the onset of muscle soreness. This special issue, therefore, serves as a launching pad for a much-needed research agenda. It invites scholars and practitioners alike to engage with and further investigate the relationship between fatigue and motor control skills, thereby contributing to our growing understanding and knowledge of this pivotal area.

Does footedness affect bilateral plantar flexor responses to sudden stance perturbations under unilateral lower leg muscular fatigue?

Carla D. P. Rinaldin — 2023-09-30

BACKGROUND: Analysis of performance asymmetries has indicated that the right and left cerebral hemispheres are specialized for specific functions of motor control.

AIM: In the current investigation, we aimed to evaluate the effect of leg dominance on electrical activation of the plantar flexor muscles in responses to unanticipated stance perturbations in a state muscular fatigue of the dominant leg.

METHOD: Fatigue was induced through ankle isometric contraction targeting 40% of maximum voluntary contraction. Muscle activation of the triceps surae of the dominant and non-dominant legs were compared in reactive responses to unanticipated load released from the trunk, leading to forward body sway. Muscular responses were analyzed in two states: pre-fatigue and fatigue of the triceps surae muscles of the dominant leg only.

RESULTS: Analysis of magnitude of muscular activation for balance recovery following perturbations revealed fatigue-related compensatory activation in the lateral gastrocnemius muscle, as indicated by over-activation of the non-fatigued/non-dominant leg to compensate for the low muscular activation of the dominant/fatigued leg in the unilateral fatigue state.

CONCLUSION: Compensatory behavior between the legs was not evident in the medial gastrocnemius and soleus muscles. Lack of effects related to leg dominance indicates that footedness did not affect automatic muscular responses either in the pre-fatigue or fatigue states.

Fatigue effect on muscle coactivation during inversion movement in females with chronic ankle instability

Thiago T. Teruya — 2023-09-30

BACKGROUND: An ankle sprain is a relevant public health issue. Fatigue changes the neuromuscular response in people with chronic ankle instability (CAI).

AIM: To evaluate the muscle co-activation on people with chronic ankle instability using cross-correlation analysis.

METHOD: Twenty-four healthy women were selected and divided into stability and instability groups. Ankle sprain was simulated with a mechanical platform. Electrical muscle activity (fibularis brevis, FB; fibularis longus, FL; gastrocnemius lateralis, GL; and tibialis anterior, TA) and platform acceleration were recorded at 2KHz. Two sets of 8 right and eight left foot fall in random order were performed before and after the fatigue protocol. Fatigue protocol ended when the volunteer increased the test run time by 150% of the best round. Co-activation was calculated with cross-correlation. Agonist-agonist (FB-FL, FB-GL, and FL-GL) and agonist-antagonist (TA-GL, TA-FB, and TA-FL) pairs were evaluated. Statistical significance was p<0.05.

RESULTS: Co-activation was lower for the instability group. Fatigue did not induce changes in 5 out of the 6 analyzed muscle pairs.

CONCLUSION: CAI is a factor of joint instability. Fatigue may not be relevant in altering joint stability. Therefore, interventions should be focused on enhancing joint stability.

A single session of hip abductors resistance exercise until failure changes shank muscle activation during landing tasks

Fabrício Cemin — 2023-09-30

BACKGROUND: Weakness in the hip abductors can lead to lower limb misalignment and an elevated risk of injury. This can result in compensatory mechanisms at the ankle to maintain stability.

AIM: To verify the effects of a single session of hip abductors resistance exercise until failure on the foot pronation and EMG amplitude of shank muscles (peroneus longus - PL; tibialis anterior - TA) during landing tasks.

METHOD: Seventeen participants completed single-leg and double-leg landings both before and after a single session of hip abductors resistance exercise until failure. The exercise consisted of four sets of 10 repetitions maximum, with a 2-minute rest interval between each set. Measurements of PL and TA EMG amplitude and degree of foot pronation were performed during landings.

RESULTS: We observed a greater degree of supination of the foot during single-leg compared to double-leg landing (p=0.006), without effect of exercise. Regarding TA EMG amplitude, there was no exercise effect (p=0.951), with a higher amplitude observed in double-leg compared to single-leg landing (p=0.001). EMG amplitude of PL was higher during single-leg compared to double-leg landing (p=0.003) and the exercise significantly reduced its activation in both tasks (p=0.032).

CONCLUSION: Single-leg and double-leg landings exhibited variations in mechanics and activation patterns of the distal muscles. Following a single session of hip abductors resistance exercise until failure, there was a reduction in PL activation during landing tasks. This suggests that there were neuromuscular compensations occurring distally due to alterations in the hip abductor muscles.

Sex differences in delayed onset muscle soreness induced by fatigue and measured by different methods

Andressa L. Lemos — 2023-09-30

BACKGROUND: Controversial outcomes from different methods for assessment of delayed onset muscle soreness (DOMS) in male and female may influence clinical decisions.

AIM: In this study, we determine sex differences in pain perception and pain thresholds in a DOMS condition resultant of a fatigue protocol.

METHOD: 11 male and 15 female healthy adults were submitted to an exercise fatigue protocol to induce DOMS in the quadriceps muscles. Pain perception was determined using a numeric pain rate scale (NRS) and pressure pain thresholds (PPT) were determined by mechanical pressure in the vastus lateralis (VL) and rectus femoris (RF) regions. Data were compared between methods and sexes at baseline, immediately after (0h), and 48 h after DOMS induction.

RESULTS: Results showed normalized lower PPT and higher NRS outcomes after fatigue, without sex differences. Absolute values of PPT showed lower values in females comparing both time and sex (VL and RF, baseline p =0.002 and p =0.009; 0h p= 0.002 and p = 0.001; 48h p<0.001 and p<0.001) with a mean difference for females and males on 0h and 48h of from baseline VL 16,52% and 19.7%; -15.64% and -10.89%; RF 12.18% and 20.7%; -9.18% and -1.97%. No correlations were found between the number of repetitions of exercise nor the rate of perceived effort and DOMS outcomes.

CONCLUSION: Men and women show similar DOMS when NRS and normalized PPT outcomes are considered. Absolute PPT values may lead to a confusing analysis of fatigue exercise-induced DOMS if merging both sexes in the sample.

Use of force plates to investigate human motor performance

Ana Maria F. Barela — 2023-09-30

Force plates have commonly been used to measure ground reaction forces. The acquired signals can be used to calculate several parameters for different motor tasks performed by human beings. Therefore, the goal of this tutorial is to present general information regarding the most common force plates, as well as their descriptions in terms of their structures, setup procedures, and signal acquisition, conversion, and export functions. This tutorial primarily provides information for those interested in using force plates to investigate human performances in the fields of motor behavior and biomechanics.