EMG normalization to study muscle activation in cycling

Effect of repeated sessions of transcranial direct current stimulation on subjective and objective measures of recovery and performance in soccer players following a soccer match simulation

We investigated the effect of repeated sessions of anodal transcranial direct current stimulation (a-tDCS) on subjective and objective measures of recovery, cognitive and sport-specific performance in professional soccer players following a soccer match simulation (SMS). Sixteen soccer players participated in this randomized, crossover, and sham-controlled study. They completed baseline assessments of well-being, total quality recovery (TQR), electromyographic activity (EMG) of the thigh muscles, countermovement jump (CMJ), and cognitive and Loughborough soccer passing test (LSPT) skills. Then, the participants engaged in an SMS routine (2 × 45 min, 15-min intervals). There was no significant difference in rating of perceived exertion (RPE) during the SMS in the anodal (17.25 ± 0.85) and sham (16.93 ± 0.92) conditions (p = 0.19). Following the SMS, the participants were randomized to receive three sessions of a-tDCS (2 mA, 20 min, +F3/-F4) targeting the left dorsolateral prefrontal cortex (DLPFC) or sham immediately after, 24 h, and 48 h after the SMS. Finally, the same outcome measures were evaluated 24 and 48 h following the SMS. A two-way repeated-measures ANOVA showed that a-tDCS stimulation improved passing skills (decreased time to perform the LSPT and number of errors; all ps < 0.01; d = 0.56-2.9) and increased the feeling of well-being (p = 0.02; d = 2.8), with no effect on TQR, cognitive performance, CMJ performance, and EMG. Therefore, the results of the present study indicate, for the first time, that repeated a-tDCS could be used as an adjunct method to accelerate soccer players' well-being and technical performance recovery, particularly after congested matches and/or training sessions. These findings may also be applicable to other team sports with characteristics similar to soccer (e.g., futsal, handball, basketball, etc.).

Estimation of joint torque in dynamic activities using wearable A-mode ultrasound

The human body constantly experiences mechanical loading. However, quantifying internal loads within the musculoskeletal system remains challenging, especially during unconstrained dynamic activities. Conventional measures are constrained to laboratory settings, and existing wearable approaches lack muscle specificity or validation during dynamic movement. Here, we present a strategy for estimating corresponding joint torque from muscles with different architectures during various dynamic activities using wearable A-mode ultrasound. We first introduce a method to track changes in muscle thickness using single-element ultrasonic transducers. We then estimate elbow and knee torque with errors less than 7.6% and coefficients of determination (R2) greater than 0.92 during controlled isokinetic contractions. Finally, we demonstrate wearable joint torque estimation during dynamic real-world tasks, including weightlifting, cycling, and both treadmill and outdoor locomotion. The capability to assess joint torque during unconstrained real-world activities can provide new insights into muscle function and movement biomechanics, with potential applications in injury prevention and rehabilitation.

Older adults use fewer muscles to overcome perturbations during a seated locomotor task

Locomotor perturbations provide insights into humans' response to motor errors. We investigated the differences in motor adaptation and muscle cocontraction between young and older adults during perturbed-arm and -leg recumbent stepping. We hypothesized that besides prolonged adaptation due to use-dependent learning, older adults would exhibit greater muscle cocontraction than young adults in response to the perturbations. Perturbations were brief increases in resistance applied during each stride at the extension onset or midextension of the left or right leg. Seventeen young adults and eleven older adults completed four 10-min perturbed stepping tasks. Subjects were instructed to follow a visual pacing cue, step smoothly, and use all their limbs to drive the stepper. Results showed that young and older adults did not decrease their errors with more perturbation experience, and errors did not wash out after perturbations were removed. Interestingly, older adults consistently had smaller motor errors than young adults in response to the perturbations. Older adults used fewer muscles to drive the stepper and had greater cocontraction than young adults. The results suggest that, despite similar motor error responses, young and older adults use distinctive muscle recruitment patterns to perform the motor task. Age-related motor strategies help track motor changes across the human life span and are a baseline for rehabilitation and performance assessment.NEW & NOTEWORTHY Older adults often demonstrate greater cocontraction and motor errors than young adults in response to motor perturbations. We demonstrated that older adults reduced their motor errors more than young adults with brief perturbations during recumbent stepping while maintaining greater muscle cocontraction. In doing so, older adults largely used one muscle pair to drive the stepper, tibialis anterior and soleus, whereas young adults used all muscles. These two muscles are crucial for maintaining upright balance.

The lactate response to a second bout of exercise is not reduced in a concurrent lower-limb exercise program

We aimed to evaluate the blood lactate level in response to two bouts of exercise. First, we hypothesized that blood lactate elevation in response to moderate-intensity aerobic exercise (MIAE) would be lower at the end of the second bout of MIAE than the first bout of MIAE. In this context, we also hypothesized that lactate accumulation at the end of resistance exercise (RE) would be reduced if MIAE is performed before RE (i.e., concurrent exercise; CE). If so, we hypothesized that the order of the CE (i.e., RE + MIAE vs. MIAE + RE) influences blood lactate kinetics. To test the hypotheses, forty-three healthy men participated in three studies. In study 1, 20 men (age 21 ± 2 years) performed two bouts of a 20-min MIAE separated by a 20-min rest interval. In study 2, 11 men (age 22 ± 1 years) performed RE only and CE (MIAE + RE; ARCE) with a 20-min rest interval in a crossover design. In study 3, 12 men (age 21 ± 2 years) performed both CEs, which were ARCE and RE + MIAE (RACE), with a 20-min rest interval in a crossover design. We measured blood lactate before and at the end of each exercise session. In study 1, the blood lactate response to the second bout of MIAE was lower than that of the first bout (P < 0.001, r = 0.68). However, the blood lactate response to the ARCE trial was not lower than the response to the RE trial in study 2 (P = 0.475, r = 0.22). The results of study 3 showed that the RACE and ARCE trials induced a similar lactate response (MIAE P = 0.423, r = 0.28; RE P = 0.766, d = 0.03). These observations indicate that whereas lactate accumulation might be diminished by a second bout of MIAE, a different type of exercise (i.e., aerobic/resistance) did not result in a diminished lactate accumulation in response to a second bout of exercise.

Lower limb muscle activity during first and second tennis serves: a comparison of three surface electromyography normalisation methods

We assessed lower limb muscle activity during the execution of first and second tennis serves, exploring whether the extent of these differences is influenced by the chosen method for normalising surface electromyography (EMG) data. Ten male competitive tennis players first completed three rounds of maximal isometric voluntary contractions (MVC) of knee extensors and plantar flexors for the left (front) and right (back) leg separately, and three squat jumps. Afterward, they executed ten first and ten-second serves. Surface EMG activity of four lower limb muscles (vastus lateralis, rectus femoris, gastrocnemius lateralis, and soleus muscles) on each leg was recorded and normalised in three different ways: to MVC; to peak/maximal activity measured during squat jump; and to the actual serve. For the rectus femoris and soleus muscles of the left leg, and the gastrocnemius lateralis and soleus muscles of the right leg, EMG amplitude differed significantly between normalisation techniques (P ≤ 0.012). All muscles showed greater activity during the first serve, although this difference was only statistically significant for the right vastus lateralis muscle (P = 0.014). In conclusion, the EMG normalisation method selected may offer similar information when comparing first and second serve, at least for leg muscles studied here.

Individual Muscle Force Estimation in the Human Forearm Using Multi-Muscle MR Elastography (MM-MRE)

OBJECTIVE

To establish the sensitivity of magnetic resonance elastography (MRE) to active muscle contraction in multiple muscles of the forearm.

METHODS

We combined MRE of forearm muscles with an MRI-compatible device, the MREbot, to simultaneously measure the mechanical properties of tissues in the forearm and the torque applied by the wrist joint during isometric tasks. We measured shear wave speed of thirteen forearm muscles via MRE in a series of contractile states and wrist postures and fit these outputs to a force estimation algorithm based on a musculoskeletal model.

RESULTS

Shear wave speed changed significantly upon several factors, including whether the muscle was recruited as an agonist or antagonist (p = 0.0019), torque amplitude (p = <0.0001), and wrist posture (p = 0.0002). Shear wave speed increased significantly during both agonist (p = <0.0001) and antagonist (p = 0.0448) contraction. Additionally, there was a greater increase in shear wave speed at greater levels of loading. The variations due to these factors indicate the sensitivity to functional loading of muscle. Under the assumption of a quadratic relationship between shear wave speed and muscle force, MRE measurements accounted for an average of 70% of the variance in the measured joint torque.

CONCLUSION

This study shows the ability of MM-MRE to capture variations in individual muscle shear wave speed due to muscle activation and presents a method to estimate individual muscle force through MM-MRE derived measurements of shear wave speed.

SIGNIFICANCE

MM-MRE could be used to establish normal and abnormal muscle co-contraction patterns in muscles of the forearm controlling hand and wrist function.

Biomechanical comparison of human trunk and thigh muscle activity during walking and horseback riding activity

INTRODUCTION

Hippotherapy is a physical therapy tool that utilizes horseback riding to improve strength, coordination, gait, and balance. These benefits may be linked to similarities in kinematics and muscle activation between horseback riding and normal human gait, but this is not well represented in the literature, especially for muscle activation. The purpose of this study was to investigate the relationships between muscle activation of horseback riding and healthy human gait.

METHODS

The muscle activation of nine healthy female participants (age 18-22) were recorded during walking and horseback riding trials using surface electromyography (EMG). Muscles analyzed include rectus abdominis, lumbar erector spinae, rectus femoris and biceps femoris. Activation waveforms during walking and riding were generated, and from this average and maximum contraction magnitudes were recorded.

RESULTS

Average muscle activation was significantly greater in riding for the left (p = 0.008) and right (p = 0.04) biceps femoris. Additionally, average and maximal activation of the left erector spinae were significantly greater in riding (W = 4; critical value for W at n = 9 is 5). Remaining differences in muscle activation between walking and riding were non-significant.

DISCUSSION

Peak and average muscle activation magnitude across the gait cycle were similar for most muscle groups. When present, differences were greater in riding. Despite these similarities, EMG waveforms displayed more predictable temporal patterns in walking.

CONCLUSION

These findings suggest that hippotherapy could be used to elicit muscle excitation similar to that of normal gait, which may have promising implications for rehabilitation targeting gait correction.

Concomitant dual-site tDCS and dark chocolate improve cognitive and endurance performance following cognitive effort under hypoxia: a randomized controlled trial

Ten male cyclists were randomized into four experimental conditions in this randomized, cross-over, double-blind, and sham-controlled study to test the combined effect of acute dark chocolate (DC) ingestion and anodal concurrent dual-site transcranial direct current stimulation (a-tDCS) targeting M1 and left DLPFC on cognitive and whole-body endurance performance in hypoxia after performing a cognitive task. Two hours before the sessions, chocolate was consumed. After arriving at the lab, participants completed an incongruent Stroop task for 30 min in hypoxia (O2 = 13%) to induce mental fatigue, followed by 20 min of tDCS (2 mA) in hypoxia. Then, in hypoxia, they performed a time-to-exhaustion task (TTE) while measuring physiological and psychophysiological responses. Cognitive performance was measured at baseline, after the Stroop task, and during and after TTE. TTE in 'DC + a-tDCS' was significantly longer than in 'white chocolate (WC) + a-tDCS' and WC + sham-tDCS'. The vastus medialis muscle electromyography amplitude was significantly higher in 'DC + a-tDCS' and 'DC + sham-tDCS' than in 'WC + sh-tDCS'. During and after the TTE, choice reaction time was significantly lower in 'DC + a-tDCS' compared to 'WC + sh-tDCS'. Other physiological or psychophysiological variables showed no significant differences. The concurrent use of acute DC consumption and dual-site a-tDCS might improve cognitive and endurance performance in hypoxia.

Effect of tDCS targeting the M1 or left DLPFC on physical performance, psychophysiological responses, and cognitive function in repeated all-out cycling: a randomized controlled trial

BACKGROUND

Despite reporting the positive effects of transcranial direct current stimulation (tDCS) on endurance performance, very few studies have investigated its efficacy in anaerobic short all-out activities. Moreover, there is still no consensus on which brain areas could provide the most favorable effects on different performance modalities. Accordingly, this study aimed to investigate the effects of anodal tDCS (a-tDCS) targeting the primary motor cortex (M1) or left dorsolateral prefrontal cortex (DLPFC) on physical performance, psychophysiological responses, and cognitive function in repeated all-out cycling.

METHODS

In this randomized, crossover, and double-blind study, 15 healthy physically active men underwent a-tDCS targeting M1 or the left DLPFC or sham tDCS in separate days before performing three bouts of all-out 30s cycling anaerobic test. a-tDCS was applied using 2 mA for 20 min. Peak power, mean power, fatigue index, and EMG of the quadriceps muscles were measured during each bout. Heart rate, perceived exertion, affective valence, and arousal were recorded two minutes after each bout. Color-word Stroop test and choice reaction time were measured at baseline and after the whole anaerobic test.

RESULTS

Neither tDCS montage significantly changed peak power, mean power, fatigue index, heart rate, affective valence, arousal, and choice reaction time (p> 0.05). a-tDCS over DLPFC significantly lowered RPE of the first bout (compared to sham; p=0.048, Δ=-12.5%) and third bout compared to the M1 (p=0.047, Δ=-12.38%) and sham (p=0.003, Δ=-10.5%), increased EMG of the Vastus Lateralis muscle during the second (p=0.016, Δ= +40.3%) and third bout (p=0.016, Δ= +42.1%) compared to sham, and improved the score of color-word Stroop test after the repeated all-out task (p=0.04, Δ= +147%). The qualitative affective response (valence and arousal) was also higher under the M1 and DLPFC compared to the sham.

CONCLUSION

We concluded that tDCS targeting M1 or DLPFC does not improve repeated anaerobic performance. However, the positive effect of DLPFC montage on RPE, EMG, qualitative affective responses, and cognitive function is promising and paves the path for future research using different tDCS montages to see any possible effects on anaerobic performance.

TRIAL REGISTRATION

This study was approved by the Ethics Committee of Razi University (IR.RAZI.REC.1400.023) and registered in the Iranian Registry of Clinical Trials (IRCT id: IRCT20210617051606N5; Registration Date: 04/02/2022).

Anodal tDCS over the left DLPFC but not M1 increases muscle activity and improves psychophysiological responses, cognitive function, and endurance performance in normobaric hypoxia: a randomized controlled trial

BACKGROUND

Transcranial direct current stimulation (tDCS) has been shown to have positive effects on exercise performance and cognitive function in the normal ambient condition. Hypoxia is deemed a stressful situation with detrimental effects on physiological, psychological, cognitive, and perceptual responses of the body. Nevertheless, no study has evaluated the efficacy of tDCS for counteracting the negative effects of hypoxic conditions on exercise performance and cognition so far. Hence, in the present study, we investigated the effects of anodal tDCS on endurance performance, cognitive function, and perceptual responses in hypoxia.

PARTICIPANTS AND METHODS

Fourteen endurance-trained males participated in five experimental sessions. After familiarization and measuring peak power output in hypoxia, in the first and second sessions, through the 3rd to 5th sessions, participants performed a cycling endurance task until exhaustion after 30 min hypoxic exposure at resting position followed by 20 min of anodal stimulation of the motor cortex (M1), left dorsolateral prefrontal cortex (DLPFC), or sham-tDCS. Color-word Stroop test and choice reaction time were measured at baseline and after exhaustion. Time to exhaustion, heart rate, saturated O₂, EMG amplitude of the vastus lateralis, vastus medialis, and rectus femoris muscles, RPE, affective response, and felt arousal were also measured during the task under hypoxia.

RESULTS

The results showed a longer time to exhaustion (+ 30.96%, p₌0.036), lower RPE (- 10.23%, p ₌ 0.045) and higher EMG amplitude of the vastus medialis muscle (+ 37.24%, p₌0.003), affective response (+ 260%, p₌0.035) and felt arousal (+ 28.9%, p₌0.029) in the DLPFC tDCS compared to sham. The choice reaction time was shorter in DLPFC tDCS compared to sham (- 17.55%, p₌0.029), and no differences were seen in the color-word Stroop test among the conditions under hypoxia. M1 tDCS resulted in no significant effect for any outcome measure.

CONCLUSIONS

We concluded that, as a novel finding, anodal stimulation of the left DLPFC might provide an ergogenic aid for endurance performance and cognitive function under the hypoxic condition probably via increasing neural drive to the working muscles, lowering RPE, and increasing perceptual responses.

The effect of muscle atrophy in people with unilateral transtibial amputation for three activities: Gait alone does not tell the whole story

Amputation imposes significant challenges in locomotion to millions of people with limb loss worldwide. The decline in the use of the residual limb results in muscle atrophy that affects musculoskeletal dynamics in daily activities. The aim of this study was to quantify the lower limb muscle volume discrepancy based on magnetic resonance (MR) imaging and to combine this with motion analysis and musculoskeletal modelling to quantify the effects in the dynamics of key activities of daily living. Eight male participants with traumatic unilateral transtibial amputation were recruited who were at least six months after receiving their definitive prostheses. The muscle volume discrepancies were found to be largest at the knee extensors (35 %, p = 0.008), followed by the hip abductors (17 %, p = 0.008). Daily activities (level walking, standing up from a chair and ascending one step) were measured in a motion analysis laboratory and muscle and joint forces quantified using a detailed musculoskeletal model for people with unilateral transtibial amputation which was calibrated in terms of the muscle volume discrepancies post-amputation at a subject-specific level. Knee extensor muscle forces were lower at the residual limb than the intact limb for all activities (p ≤ 0.008); residual limb muscle forces of the hip abductors (p ≤ 0.031) and adductors (p ≤ 0.031) were lower for standing-up and ascending one step. While the reduced knee extensor force has been reported by other studies, our results suggest a new biomechanically-based mitigation strategy to improve functional mobility, which could be achieved through strengthening of the hip abd/adductor muscles.

Feature–Classifier Pairing Compatibility for sEMG Signals in Hand Gesture Recognition under Joint Effects of Processing Procedures

Gesture recognition using surface electromyography (sEMG) serves many applications, from human–machine interfaces to prosthesis control. Many features have been adopted to enhance recognition accuracy. However, studies mostly compare features under a prechosen feature window size or a classifier, biased to a specific application. The bias is evident in the reported accuracy drop, around 10%, from offline gesture recognition in experiment settings to real-time clinical environment studies. This paper explores the feature–classifier pairing compatibility for sEMG. We demonstrate that it is the primary determinant of gesture recognition accuracy under various window sizes and normalization ranges, thus removing application bias. The proposed pairing ranking provides a guideline for choosing the proper feature or classifier in future research. For instance, random forest (RF) performed best, with a mean accuracy of around 74.0%; however, it was optimal with the mean absolute value feature (MAV), giving 86.8% accuracy. Additionally, our ranking showed that the proper pairing enables low-computational models to surpass complex ones. The Histogram feature with linear discriminant analysis classifier (HIST-LDA) was the top pair with 88.6% accuracy. We also concluded that a 1250 ms window and a (−1, 1) signal normalization were the optimal procedures for gesture recognition on the used dataset.

Quadriceps Muscle Fatigue Reduces Extension and Flexion Power During Maximal Cycling

Purpose: To investigate how quadriceps muscle fatigue affects power production over the extension and flexion phases and muscle activation during maximal cycling. Methods: Ten participants performed 10-s maximal cycling efforts without fatigue and after 120 bilateral maximal concentric contractions of the quadriceps muscles. Extension power, flexion power and electromyographic (EMG) activity were compared between maximal cycling trials. We also investigated the associations between changes in quadriceps force during isometric maximal voluntary contractions (IMVC) and power output (flexion and extension) during maximal cycling, in addition to inter-individual variability in muscle activation and pedal force profiles. Results: Quadriceps IMVC (-52 ± 21%, P = 0.002), voluntary activation (-24 ± 14%, P < 0.001) and resting twitch amplitude (-45 ± 19%, P = 0.002) were reduced following the fatiguing task, whereas vastus lateralis (P = 0.58) and vastus medialis (P = 0.15) M-wave amplitudes were unchanged. The reductions in extension power (-15 ± 8%, P < 0.001) and flexion power (-24 ± 18%, P < 0.001) recorded during maximal cycling with fatigue of the quadriceps were dissociated from the decreases in quadriceps IMVC. Peak EMG decreased across all muscles while inter-individual variability in pedal force and EMG profiles increased during maximal cycling with quadriceps fatigue. Conclusion: Quadriceps fatigue induced by voluntary contractions led to reduced activation of all lower limb muscles, increased inter-individual variability and decreased power production during maximal cycling. Interestingly, power production was further reduced over the flexion phase (24%) than the extension phase (15%), likely due to larger levels of peripheral fatigue developed in RF muscle and/or a higher contribution of the quadriceps muscle to flexion power production compared to extension power during maximal cycling.

Neuromuscular responses at acute moderate and severe hypoxic exposure during fatiguing exercise of the biceps brachii

Purpose

The present study examined acute normobaric hypoxic exposure on the number of repetitions to failure, electromyographic (EMG) repetition duration (Time), EMG root mean square (RMS) and EMG mean power frequency (MPF) during biceps brachii (BB) dynamic constant external resistance (DCER) exercise.

Methods

Thirteen subjects performed two sets of fatiguing DCER arm curl repetitions to failure at 70% of their one repetition maximum under normoxic (NH), moderate hypoxia FiO₂ = 15% (MH) and severe hypoxia FiO₂ = 13% (SH). Electromyography of the BB was analyzed for EMG Time, EMG RMS, and EMG MPF. Repetitions were selected as 25%, 50%, 75%, and 100% of total repetitions (%Fail) completed. Pulse oximetry (SpO₂) was measured pre-and post-fatigue.

Results

There was no significant three-way (Condition x Set x %Fail) or two-way (Condition x Set) interaction for any variable. The number of repetitions to failure significantly decreased from (mean ± SEM) 18.2 ± 1.4 to 9.5 ± 1.0 with each Set. In addition, EMG Time increased (25% < 50%<75% < 100%), EMG RMS decreased (50% > 75%>100%), and EMG MPF decreased (75% > 100%) as a result of fatiguing exercise. SpO₂ was lower during MH (Δ5.3%) and SH (Δ9.2%) compared to NH and as a result of fatiguing exercise increased only in MH (Δ2.1%) and SH (Δ5.7%).

Conclusion

The changes in BB EMG variables indicated exercise caused myoelectric manifestations of fatigue, however, acute moderate or severe hypoxia had no additional influence on the rate of fatigue development or neuromuscular parameters.

•

Acute MH (FiO₂ 15%) and SH (FiO₂ 14%) did not alter the muscle contractile process.

•

Arm curl repetitions to failure decreased MU recruitment and conduction velocity.

•

EMG fatigue analysis, hypoxia and arm curls to failure, EMG RMS, EMG MPF and Time.

•

SpO₂ was lower at MH and SH which increased following fatiguing exercise.

Processing of EMG Signals with High Impact of Power Line and Cardiac Interferences

This work deals with electromyography (EMG) signal processing for the diagnosis and therapy of different muscles. Because the correct muscle activity measurement of strongly noised EMG signals is the major hurdle in medical applications, a raw measured EMG signal should be cleaned of different factors like power network interference and ECG heartbeat. Unfortunately, there are no completed studies showing full multistage signal processing of EMG recordings. In this article, the authors propose an original algorithm to perform muscle activity measurements based on raw measurements. The effectiveness of the proposed algorithm for EMG signal measurement was validated by a portable EMG system developed as a part of the EU research project and EMG raw measurement sets. Examples of removing the parasitic interferences are presented for each stage of signal processing. Finally, it is shown that the proposed processing of EMG signals enables cleaning of the EMG signal with minimal loss of the diagnostic content.

Impact of Power Output on Muscle Activation and 3D Kinematics During an Incremental Test to Exhaustion in Professional Cyclists

This study aimed to quantify the influence of an increase in power output (PO) on joint kinematics and electromyographic (EMG) activity during an incremental test to exhaustion for a population of professional cyclists. The hip flexion/extension and internal/external rotation as well as knee abduction/adduction ranges of motion were significantly decreased at 100% of the maximal aerobic power (MAP). EMG analysis revealed a significant increase in the root mean square (RMS) for all muscles from 70% of the MAP. Gastrocnemius muscles [lateralis gastrocnemius (GasL) and medialis gastrocnemius (GasM)] were the less affected by the increase of PO. Cross-correlation method showed a significant increase in the lag angle values for VM in the last stage compared to the first stage, meaning that the onset of the activation started earlier during the pedaling cycle. Statistical Parametric Mapping (SPM) demonstrated that from 70% MAP, biceps femoris (BF), tibialis anterior (TA), gluteus maximus (GM), and rectus femoris (RF) yielded larger ranges of the crank cycle on which the level of recruitment was significantly increased. This study revealed specific muscular and kinematic coordination for professional cyclists in response to PO increase.

Effects of gravity and kinematic constraints on muscle synergies in arm cycling

Arm cycling is a bimanual motor task used in medical rehabilitation and in sports training. Understanding how muscle coordination changes across different biomechanical constraints in arm cycling is a step toward improved rehabilitation approaches. This exploratory study aims to get new insights on motor control during arm cycling. To achieve our main goal, we used the muscle synergies analysis to test three hypotheses: 1) body position with respect to gravity (sitting and supine) has an effect on muscle synergies; 2) the movement size (crank length) has an effect on the synergistic behavior; 3) the bimanual cranking mode (asynchronous and synchronous) requires different synergistic control. Thirteen able-bodied volunteers performed arm cranking on a custom-made device with unconnected cranks, which allowed testing three different conditions: body position (sitting vs. supine), crank length (10 cm vs. 15 cm), and cranking mode (synchronous vs. asynchronous). For each of the eight possible combinations, subjects cycled for 30 s while electromyography of eight muscles (four from each arm) were recorded: biceps brachii, triceps brachii, anterior deltoid, and posterior deltoid. Muscle synergies in this eight-dimensional muscle space were extracted by nonnegative matrix factorization. Four synergies accounted for over 90% of muscle activation variances in all conditions. Results showed that synergies were affected by body position and cranking mode but practically unaffected by movement size. These results suggest that the central nervous system may employ different motor control strategies in response to external constraints such as cranking mode and body position during arm cycling.NEW & NOTEWORTHY Recent studies analyzed muscle synergies in lower limb cycling. Here, we examine upper limb cycling and specifically the effect of body position with respect to gravity, movement size, and cranking mode on muscle coordination during arm cranking tasks. We show that altered body position and cranking mode affects modular organization of muscle activities. To our knowledge, this is the first study assessing motor control through muscle synergies framework during upper limb cycling with different constraints.

Online sonification improves cycling performance through kinematic and muscular reorganisations

Based on a previous study that demonstrated the beneficial effects of sonification on cycling performance, this study investigated which kinematic and muscular activities were changed to pedal effectively. An online error-based sonification strategy was developed, such that, when negative torque was applied to the pedal, a squeak sound was produced in real-time in the corresponding headphone. Participants completed four 6-min cycling trials with resistance values associated with their first ventilatory threshold. Different auditory display conditions were used for each trial (Silent, Right, Left, Stereo), where sonification was only presented for 20 s at the start of minutes 1, 2, 3, and 4. Joint kinematics and right leg muscular activities of 10 muscles were simultaneously recorded. Our results showed participants were more effective at pedalling when presented sonification, which was consistent with previously reported findings. In comparison to the Silent condition, sonification significantly limited ankle and knee joint ranges of motion and reduced muscular activations. These findings suggest performance-based sonification significantly affected participants to reduce the complexity of the task by altering the coordination of the degrees of freedom. By making these significant changes to their patterns, participants improved their cycling performance despite lowering joint ranges of motion and muscular activations.

Walking with a powered ankle-foot orthosis: the effects of actuation timing and stiffness level on healthy users

BACKGROUND

In the last decades, several powered ankle-foot orthoses have been developed to assist the ankle joint of their users during walking. Recent studies have shown that the effects of the assistance provided by powered ankle-foot orthoses depend on the assistive profile. In compliant actuators, the stiffness level influences the actuator's performance. However, the effects of this parameter on the users has not been yet evaluated. The goal of this study is to assess the effects of the assistance provided by a variable stiffness ankle actuator on healthy young users. More specifically, the effect of different onset times of the push-off torque and different actuator's stiffness levels has been investigated.

METHODS

Eight healthy subjects walked with a unilateral powered ankle-foot orthosis in several assisted walking trials. The powered orthosis was actuated in the sagittal plane by a variable stiffness actuator. During the assisted walking trials, three different onset times of the push-off assistance and three different actuator's stiffness levels were used. The metabolic cost of walking, lower limb muscles activation, joint kinematics, and gait parameters measured during different assisted walking trials were compared to the ones measured during normal walking and walking with the powered orthosis not providing assistance.

RESULTS

This study found trends for more compliant settings of the ankle actuator resulting in bigger reductions of the metabolic cost of walking and soleus muscle activation in the stance phase during assisted walking as compared to the unassisted walking trial. In addition to this, the study found that, among the tested onset times, the earlier ones showed a trend for bigger reductions of the activation of the soleus muscle during stance, while the later ones led to a bigger reduction in the metabolic cost of walking in the assisted walking trials as compared to the unassisted condition.

CONCLUSIONS

This study presents a first attempt to show that, together with the assistive torque profile, also the stiffness level of a compliant ankle actuator can influence the assistive performance of a powered ankle-foot orthosis.

Fatigue Evaluation through Machine Learning and a Global Fatigue Descriptor

Research in physiology and sports science has shown that fatigue, a complex psychophysiological phenomenon, has a relevant impact in performance and in the correct functioning of our motricity system, potentially being a cause of damage to the human organism. Fatigue can be seen as a subjective or objective phenomenon. Subjective fatigue corresponds to a mental and cognitive event, while fatigue referred as objective is a physical phenomenon. Despite the fact that subjective fatigue is often undervalued, only a physically and mentally healthy athlete is able to achieve top performance in a discipline. Therefore, we argue that physical training programs should address the preventive assessment of both subjective and objective fatigue mechanisms in order to minimize the risk of injuries. In this context, our paper presents a machine-learning system capable of extracting individual fatigue descriptors (IFDs) from electromyographic (EMG) and heart rate variability (HRV) measurements. Our novel approach, using two types of biosignals so that a global (mental and physical) fatigue assessment is taken into account, reflects the onset of fatigue by implementing a combination of a dimensionless (0-1) global fatigue descriptor (GFD) and a support vector machine (SVM) classifier. The system, based on 9 main combined features, achieves fatigue regime classification performances of 0.82 ± 0.24, ensuring a successful preventive assessment when dangerous fatigue levels are reached. Training data were acquired in a constant work rate test (executed by 14 subjects using a cycloergometry device), where the variable under study (fatigue) gradually increased until the volunteer reached an objective exhaustion state.

Model for prompt and effective classification of motion recovery after stroke considering muscle strength and coordination factors

Background

Muscle synergies are now widely discussed as a method for evaluating the existence of redundant neural networks that can be activated to enhance stroke rehabilitation. However, this approach was initially conceived to study muscle coordination during learned motions in healthy individuals. After brain damage, there are several neural adaptations that contribute to the recovery of motor strength, with muscle coordination being one of them. In this study, a model is proposed that assesses motion based on surface electromyography (sEMG) according to two main factors closely related to the neural adaptations underlying motor recovery: (1) the correct coordination of the muscles involved in a particular motion and (2) the ability to tune the effective strength of each muscle through muscle fiber contractions. These two factors are hypothesized to be affected differently by brain damage. Therefore, their independent evaluation will play an important role in understanding the origin of stroke-related motor impairments.

Results

The model proposed was validated by analyzing sEMG data from 18 stroke patients with different paralysis levels and 30 healthy subjects. While the factors necessary to describe motion were stable across heathy subjects, there was an increasing disassociation for stroke patients with severe motor impairment.

Conclusions

The clear dissociation between the coordination of muscles and the tuning of their strength demonstrates the importance of evaluating these factors in order to choose appropriate rehabilitation therapies. The model described in this research provides an efficient approach to promptly evaluate these factors through the use of two intuitive indexes.

The musculoskeletal and cognitive effects of under-desk cycling compared to sitting for office workers

Alternate work positions are being considered as a way to address sedentary behaviour for office workers. This study evaluated the effect of two hours of just-sitting versus sitting while under-desk cycling on musculoskeletal discomfort and cognitive function (sustained attention and creative problem solving). To consider mechanisms, muscle fatigue, kinematics and mental state were also measured. Discomfort increased significantly across all body areas with knee and ankle discomfort greater (in a clinically meaningful manner) in under-desk cycling. Sustained attention reaction time was the only cognitive measure to show a difference between conditions (slower for under-desk cycling [β-34.82 CI (-62.12 to -7.53)]). There was no evidence of muscle fatigue, while kinematic differences between conditions were identified. Mental state deteriorated over time in both conditions. This study found no clear benefit of under-desk cycling compared to just-sitting for musculoskeletal health and cognitive function measures.

The Rise of Elite Short-Course Triathlon Re-Emphasises the Necessity to Transition Efficiently from Cycling to Running

Transitioning efficiently between cycling and running is considered an indication of overall performance, and as a result the cycle–run (C–R) transition is one of the most researched areas of triathlon. Previous studies have thoroughly investigated the impact of prior cycling on running performance. However, with the increasing number of short-course events and the inclusion of the mixed relay at the 2020 Tokyo Olympics, efficiently transitioning from cycle–run has been re-emphasised and with it, any potential limitations to running performance among elite triathletes. This short communication provides coaches and sports scientists a review of the literature detailing the negative effects of prior variable-cycling on running performance experienced among elite, short-course and Olympic distance triathletes; as well as discussing practical methods to minimise any negative impact of cycling on running performance. The current literature suggests that variable-cycling negatively effects running ability in at least some elite triathletes and that improving swimming performance, drafting during cycling and C–R training at race intensity could improve an athlete’s triathlon running performance. It is recommended that future research clearly define the performance level, competitive format of the experimental population and use protocols that are specific to the experimental population in order to improve the training and practical application of the research findings.

Reliability of traditional and task specific reference tasks to assess peak muscle activation during two different sprint cycling tests

Neuromuscular activation is considered an important determinant sprint cycling performance but requires reliable EMG amplitude measurements to facilitate sensitive assessments. The reliability of EMG measurements during sprint cycling may depend on the sprint cycling test undertaken (isovelocity or isoinertial accelerating), the reference tasks used for normalisation (isometric MVCs of a series of single muscle groups [ISO-SINGJT] or isometric cycling MVCs [ISO-CYC]), and the efficacy of the normalisation. This study aimed to compare the magnitude and between-session reliability of peak muscle activation (peak rmsEMG) during: isovelocity and isoinerital sprint cycling tests; ISO-SINGJT and ISO-CYC reference tasks; and absolute and normalised EMG during the sprint cycling tests. EMG amplitude was measured over six major muscle groups on both legs and all measurements were made over two sessions in a randomised counterbalanced design. Peak rmsEMG was assessed during both ISO-SINGJT and ISO-CYC MVCs and then during mechanical peak power output (PPO) during isovelocity (120 RPM) and isoinerital acceleration (0 to >150 RPM) sprint tests. Absolute peak rmsEMG and for the sprint tests normalised EMG values were determined, and coefficient of variation and intra-class correlation coefficients used to assess reliability. Peak rmsEMG at PPO during both sprint cycling tests was similar for the six muscle groups measured. Peak rmsEMG was higher during ISO-SINGJT than ISO-CYC for for 3 of the 6 muscle groups, but all muscle groups exhibited similar reliability for both reference tasks. Neither reference task improved the between-session reliability for either sprint test. This data highlights reservations in the use of isometric reference tasks to ascertain changes in peak muscle activation over time in during sprint cycling assessments.

Comparing functional dynamic normalization methods to maximal voluntary isometric contractions for lower limb EMG from walking, cycling and running

There is no consensus on the most appropriate method for normalizing an individual's electromyography (EMG) signals from walking, cycling and running in the same data collection. The aim of this study was to compare how the magnitude and repeatability of normalization values differ from three normalization methods and to compare their scaling effect in three moderate intensity activities. Three rounds of maximal voluntary isometric contractions (MVICs), sprint cycling and sprint running were performed to obtain normalization values for each method. EMG from five moderate intensity trials of walking, cycling and running were performed and normalized using each normalization value. Normalization values, coefficients of variation, and peak normalized EMG from the three moderate intensity activities were compared across normalization methods. Sprint running resulted in greater normalization values for 6/9 muscles. MVICs produced the lowest variance in 6/9 muscles. Comparing peak normalized signals of interest across normalization methods, there were significant differences in 6/9, 7/9 and 8/9 muscles for walking, cycling and running, respectively. When investigating a combination of walking, cycling and/or running EMG data, sprint running could be used for normalization, due to its simplicity and its ability to produce a larger normalization value, despite lower repeatability.

Musculoskeletal and Cognitive Effects of a Movement Intervention During Prolonged Standing for Office Work

OBJECTIVE

To investigate whether use of a movement intervention when undertaking prolonged standing affected discomfort and cognitive function.

BACKGROUND

Alternate work positions to break up prolonged sitting for office workers are being trialed, such as standing. Prolonged standing has potential negative health implications, including low back and lower limb discomfort, and may influence cognitive function. Introducing movement during standing may provide a healthy and productive alternative work posture.

METHOD

Twenty adult participants undertook a laboratory study of 2 hr of standing and standing with movement (using a footrest) while performing computer work. Changes in discomfort and cognitive function, with muscle fatigue, low back angle, pelvis movement, lower limb swelling, and mental state, were investigated.

RESULTS

Discomfort increased significantly over time across all body regions. Ankle/foot differed between conditions (incident rate ratio [95% confidence interval]: 1.89 [1.10-3.23]), with higher discomfort during standing with movement. Creative problem-solving errors increased during standing with movement and decreased during standing (Time × Condition: β = 0.64 [0.10-1.18]), with no other cognitive function measure differences. Mental state deteriorated over time for both conditions, greater during standing with movement (Time × Condition: β = 2.44 [0.23-4.66]). No significant interaction effects were found for the other outcome variables.

CONCLUSION

Standing with movement provided no advantage in discomfort or cognitive function. There were some negative effects for ankle/foot discomfort and creative problem solving. An alternate footrest design and protocol for use may yield more favorable results.

APPLICATION

Based on the results from this study, footrest use to raise alternative foot for forced 5-min intervals would not be recommended to assist with managing discomfort while prolonged standing in workplaces.

Prevalence of musculoskeletal disorders among Indian railway sahayaks

Railway sahayak or also known as coolie is one of the oldest occupations in India. This occupational group is continuously subjected to various musculoskeletal problems due to repetitive load exertion in unnatural postures. The present research aims to examine the prevalence of musculoskeletal disorders (MSDs) among Indian railway sahayaks. A cross-sectional study has been conducted on a sample of 51 male sahayaks. With a modified Nordic questionnaire, data were collected on their demographics, work, and musculoskeletal pain history. Electromyography (EMG) of the upper trapezius muscle of selected 12 healthy sahayaks having no history of neck-shoulder complaints were analyzed under different load lifting and carrying conditions. Additionally, ergonomic risk levels were recorded using Rapid Entire Body Assessment method. The questionnaire revealed that for the past 1 year prevalence, the most affected body regions of railway sahayaks were neck (47%), shoulder (51%), lower back (43%), and knee (47%). The association between age group and MSDs in different body regions were found significant (p = 0.012 for neck, p = 0.017 for shoulder, etc.). Work experience also had a significant relation to the MSDs in different body regions (p = 0.013 for shoulder,p = 0.023 for calf, etc.). Analysis of variance reveals high significance level between EMG values and tasks performed by the sahayaks. In conclusion, railway sahayaks were found to have high rate of MSDs which may be associated with lifting/carrying heavy loads in awkward postures. Ergonomic interventions must be implemented to reduce the risk level on this group of workers.

The Short Term Musculoskeletal and Cognitive Effects of Prolonged Sitting During Office Computer Work

Office workers are exposed to high levels of sedentary time. In addition to cardio-vascular and metabolic health risks, this sedentary time may have musculoskeletal and/or cognitive impacts on office workers. Participants (n = 20) undertook two hours of laboratory-based sitting computer work to investigate changes in discomfort and cognitive function (sustained attention and problem solving), along with muscle fatigue, movement and mental state. Over time, discomfort increased in all body areas (total body IRR [95% confidence interval]: 1.43 [1.33–1.53]) reaching clinically meaningful levels in the low back and hip/thigh/buttock areas. Creative problem solving errors increased (β = 0.25 [0.03–1.47]) while sustained attention did not change. There was no change in erector spinae, trapezius, rectus femoris, biceps femoris and external oblique median frequency or amplitude; low back angle changed towards less lordosis, pelvis movement increased, and mental state deteriorated. There were no substantial correlations between discomfort and cognitive function. The observed changes suggest prolonged sitting may have consequences for musculoskeletal discomfort and cognitive function and breaks to interrupt prolonged sitting are recommended.

A detailed description of the short-term musculoskeletal and cognitive effects of prolonged standing for office computer work

Due to concerns about excessive sedentary exposure for office workers, alternate work positions such as standing are being trialled. However, prolonged standing may have health and productivity impacts, which this study assessed. Twenty adult participants undertook two hours of laboratory-based standing computer work to investigate changes in discomfort and cognitive function, along with muscle fatigue, movement, lower limb swelling and mental state. Over time, discomfort increased in all body areas (total body IRR [95% confidence interval]: 1.47[1.36-1.59]). Sustained attention reaction time (β = 18.25[8.00-28.51]) deteriorated, while creative problem solving improved (β = 0.89[0.29-1.49]). There was no change in erector spinae, rectus femoris, biceps femoris or tibialis anterior muscle fatigue; low back angle changed towards less  lordosis, pelvis movement increased, lower limb swelling increased and mental state decreased. Body discomfort was positively correlated with mental state. The observed changes suggest replacing office work sitting with standing should be done with caution. Practitioner Summary: Standing is being used to replace sitting by office workers; however, there are health risks associated with prolonged standing. In a laboratory study involving 2 h prolonged standing discomfort increased (all body areas), reaction time and mental state deteriorated while creative problem-solving improved. Prolonged standing should be undertaken with caution.

Geometric models to explore mechanisms of dynamic shape change in skeletal muscle

Skeletal muscle bulges when it contracts. These three-dimensional (3D) dynamic shape changes play an important role in muscle performance by altering the range of fascicle velocities over which a muscle operates. However traditional muscle models are one-dimensional (1D) and cannot fully explain in vivo shape changes. In this study we compared medial gastrocnemius behaviour during human cycling (fascicle length changes and rotations) predicted by a traditional 1D Hill-type model and by models that incorporate two-dimensional (2D) and 3D geometric constraints to in vivo measurements from B-mode ultrasound during a range of mechanical conditions ranging from 14 to 44 N m and 80 to 140 r.p.m. We found that a 1D model predicted fascicle lengths and pennation angles similar to a 2D model that allowed the aponeurosis to stretch, and to a 3D model that allowed for aponeurosis stretch and variable shape changes to occur. This suggests that if the intent of a model is to predict fascicle behaviour alone, then the traditional 1D Hill-type model may be sufficient. Yet, we also caution that 1D models are limited in their ability to infer the mechanisms by which shape changes influence muscle mechanics. To elucidate the mechanisms governing muscle shape change, future efforts should aim to develop imaging techniques able to characterize whole muscle 3D geometry in vivo during active contractions.

Force-velocity test on a stationary cycle ergometer: methodological recommendations

Force-velocity tests performed on stationary cycle ergometers are widely used to assess the torque- and power-generating capacities of the lower limbs. The aim of this study was to identify how testing and modeling procedures influence the assessment of individual torque-cadence and power-cadence relationships. Seventeen males completed 62 ± 16 pedal cycles from six 6-s all-out efforts interspersed with 5 min of rest. True measures of maximal power for a particular cadence were obtained for 24 ± 3 pedal cycles, while power was only 94 ± 3% of the true maximum in 19 ± 5 pedal cycles. Pedal cycles showing maximal levels of power also displayed higher levels of electromyography (EMG: 89 ± 7 vs . 87 ± 7%) and coactivation (34 ± 11 vs . 31 ± 10 arbitrary units), as well as lower variability in crank torque and EMG profiles. Compared with the linear and second-order polynomial models that are traditionally used, a better goodness of fit was obtained when the torque-cadence and power-cadence relationships were predicted using second- and third-order polynomials, respectively. The later modeling procedures also revealed an asymmetry in the power-cadence relationship in most participants (i.e., 15 out of 17) and provided a better estimation of maximal cadence [Cmax: 214 ± 20 revolutions/min (rpm)] from the x-intercept of power-cadence relationships (C0: 214 ± 14 rpm). Therefore, we recommend predicting the individual shapes of torque- and power-cadence relationships using second- and third-order polynomial regressions after having selected pedal cycles during which true measures of cadence-specific maximal power were recorded.

NEW & NOTEWORTHY This study is the first to demonstrate that suboptimal activation of the lower limb muscles accompanied reductions in cadence-specific levels of torque and power produced during a force-velocity test performed on a stationary cycle ergometer. This research is also the first to show that, in most noncyclist participants, torque-cadence relationships are not linear, whereas power-cadence relationships display asymmetric shapes, with power production decreasing rapidly when cadence increases beyond 180 revolutions/min.

Development of practical functional electrical stimulation cycling systems based on an electromyography study of the Cybathlon 2016

The purpose of this study was to develop a functional electrical stimulation (FES) system based on the motor driving concept for use by spinal cord injury patients participating in the FES Cycling competition at the Cybathlon 2016. The proposed FES system consists of a low-power control system, a precise processor unit, and a 4-channel stimulation unit. Self-adhesive carbon conductive electrodes were utilized for stimulation. A 26-year-old SCI patient was qualified to participate in the competition. The pilot patient underwent training for 16 months, which included experience with FES stimulation, performing FES cycling, and reducing spasticity, to practice using the FES system. In addition, using surface electromyography (EMG) during cycling, the muscle activation pattern for generating the stimulation profile was applied and resulted in good performance. The best FES cycling performance the pilot achieved was 1000 meters translation with the cycling system during twelve minutes of using the FES system. The pilot achieved an 1000 meters translation mobility within an average of 16 minutes of cycling. Nevertheless, the system must be further investigated regarding muscle fatigue and other factors that may affect the stimulation conditions.

Shifting gears: dynamic muscle shape changes and force-velocity behavior in the medial gastrocnemius

When muscles contract, they bulge in thickness or in width to maintain a (nearly) constant volume. These dynamic shape changes are tightly linked to the internal constraints placed on individual muscle fibers and play a key functional role in modulating the mechanical performance of skeletal muscle by increasing its range of operating velocities. Yet to date we have a limited understanding of the nature and functional implications of in vivo dynamic muscle shape change under submaximal conditions. This study determined how the in vivo changes in medial gastrocnemius (MG) fascicle velocity, pennation angle, muscle thickness, and subsequent muscle gearing varied as a function of force and velocity. To do this, we obtained recordings of MG tendon length, fascicle length, pennation angle, and thickness using B-mode ultrasound and muscle activation using surface electromyography during cycling at a range of cadences and loads. We found that that increases in contractile force were accompanied by reduced bulging in muscle thickness, reduced increases in pennation angle, and faster fascicle shortening. Although the force and velocity of a muscle contraction are inversely related due to the force-velocity effect, this study has shown how dynamic muscle shape changes are influenced by force and not influenced by velocity.NEW & NOTEWORTHY During movement, skeletal muscles contract and bulge in thickness or width. These shape changes play a key role in modulating the performance of skeletal muscle by increasing its range of operating velocities. Yet to date the underlying mechanisms associated with muscle shape change remain largely unexplored. This study identified muscle force, and not velocity, as the mechanistic driving factor to allow for muscle gearing to vary depending on the contractile conditions during human cycling.

Knee extensor fatigue developed during high-intensity exercise limits lower-limb power production

We investigated the association between changes in vastii electromyography (EMG) and knee extensor fatigue during high-intensity cycling, and the subsequent effect on lower-limb power and intermuscular coordination during all-out cycling. On two separate days, participants completed 30-s all-out cycling or 10-min of high-intensity cycling followed by 30-s all-out cycling. EMG for gluteus maximus (GMAX), rectus femoris (RF), vastii (VAS), hamstrings (HAM) and gastrocnemius (GAS); co-activation for GMAX/RF, VAS/HAM and VAS/GAS; isometric maximal voluntary force (IMVF) and resting twitch (RT) of the knee extensors were measured. VAS EMG increases during high-intensity cycling (6% to 14%, P < 0.05) were negatively correlated (r = -0.791, P < 0.05) with knee extensor IMVF decreases (-2% to-36%, P < 0.05) following the exercise. Knee extensor IMVF decreases were positively correlated (r = 0.757, P < 0.05) with all-out cycling power reductions (0% to -27%, P < 0.05). VAS/GAS co-activation did not change (P > 0.05) during all-out cycling while VAS and GAS EMG decreased. Larger increase in VAS EMG during high-intensity cycling was associated with greater knee extensor fatigue and larger power reduction during all-out cycling. High VAS/GAS co-activation potentially limited power reduction induced by knee extensor fatigue during all-out cycling.

Muscle fatigue in participants of indoor cycling

BACKGROUND

Indoor Cycling (IC) has been gaining recognition and popularity within recent years and few studies have investigated its benefits for sedentary participants.

OBJECTIVE

The aim of this study was to evaluate differences in the surface electromyography (sEMG) variables, heart rate (HR), and subjective effort in sedentary participants while they performed an IC session and to compare their results with the trained subjects, to answer the question: Are trained cyclists less susceptible to muscle fatigue, since it is expected that they make less effort?

DESIGN

Twenty-six volunteers were split into two groups according to their fitness status and weekly training load. Each participant completed an IC session in a private gym, lasting 45 minutes and were encouraged to follow the pedaling frequency and cycle resistance, within their limitations. Main Outcome Measures: HR, participants' subjective effort on the Borg Scale of Perceived Exertion (Borg Scale) and sEMG data were compared between groups.

RESULTS

28.6% of the sedentary participants withdrew from the study. Exercise intensity, assessed using the HR, was similar in both groups. The subjective perceived effort, assessed using the Borg Scale, was significantly higher in the sedentary group. All muscles considered in the sedentary group had higher variation levels of Root Mean Square (RMS) and Median Frequency (MF) than those in the trained group.

CONCLUSION

Sedentary participants are more likely to present fatigue and IC can be incorporated into protocols for this population, but their fitness levels should be taken into account because each performance depends on the individual's physical fitness.

LEVEL OF EVIDENCE

IIIb.

Relation between Peak Power Output in Sprint Cycling and Maximum Voluntary Isometric Torque Production

From a cycling paradigm, little has been done to understand the relationships between maximal isometric strength of different single joint lower body muscle groups and their relation with, and ability to predict PPO and how they compare to an isometric cycling specific task. The aim of this study was to establish relationships between maximal voluntary torque production from isometric single-joint and cycling specific tasks and assess their ability to predict PPO. Twenty male trained cyclists participated in this study. Peak torque was measured by performing maximum voluntary contractions (MVC) of knee extensors, knee flexors, dorsi flexors and hip extensors whilst instrumented cranks measured isometric peak torque from MVC when participants were in their cycling specific position (ISOCYC). A stepwise regression showed that peak torque of the knee extensors was the only significant predictor of PPO when using SJD and accounted for 47% of the variance. However, when compared to ISOCYC, the only significant predictor of PPO was ISOCYC, which accounted for 77% of the variance. This suggests that peak torque of the knee extensors was the best single-joint predictor of PPO in sprint cycling. Furthermore, a stronger prediction can be made from a task specific isometric task.

The Advantages of Normalizing Electromyography to Ballistic Rather than Isometric or Isokinetic Tasks

Isometric tasks have been a standard for electromyography (EMG) normalization stemming from anatomic and physiologic stability observed during contraction. Ballistic dynamic tasks have the benefit of eliciting maximum EMG signals for normalization, despite having the potential for greater signal variability. It is the purpose of this study to compare maximum voluntary isometric contraction (MVIC) to nonisometric tasks with increasing degrees of extrinsic variability, ie, joint range of motion, velocity, rate of contraction, etc., to determine if the ballistic tasks, which elicit larger peak EMG signals, are more reliable than the constrained MVIC. Fifteen subjects performed MVIC, isokinetic, maximum countermovement jump, and sprint tasks while EMG was collected from 9 muscles in the quadriceps, hamstrings, and lower leg. The results revealed the unconstrained ballistic tasks were more reliable compared to the constrained MVIC and isokinetic tasks for all triceps surae muscles. The EMG from sprinting was more reliable than the constrained cases for both the hamstrings and vasti. The most reliable EMG signals occurred when the body was permitted its natural, unconstrained motion. These results suggest that EMG is best normalized using ballistic tasks to provide the greatest within-subject reliability, which beneficially yield maximum EMG values.

Comparison of human gastrocnemius forces predicted by Hill-type muscle models and estimated from ultrasound images

Hill-type models are ubiquitous in the field of biomechanics, providing estimates of a muscle's force as a function of its activation state and its assumed force-length and force-velocity properties. However, despite their routine use, the accuracy with which Hill-type models predict the forces generated by muscles during submaximal, dynamic tasks remains largely unknown. This study compared human gastrocnemius forces predicted by Hill-type models with the forces estimated from ultrasound-based measures of tendon length changes and stiffness during cycling, over a range of loads and cadences. We tested both a traditional model, with one contractile element, and a differential model, with two contractile elements that accounted for independent contributions of slow and fast muscle fibres. Both models were driven by subject-specific, ultrasound-based measures of fascicle lengths, velocities and pennation angles and by activation patterns of slow and fast muscle fibres derived from surface electromyographic recordings. The models predicted, on average, 54% of the time-varying gastrocnemius forces estimated from the ultrasound-based methods. However, differences between predicted and estimated forces were smaller under low speed-high activation conditions, with models able to predict nearly 80% of the gastrocnemius force over a complete pedal cycle. Additionally, the predictions from the Hill-type muscle models tested here showed that a similar pattern of force production could be achieved for most conditions with and without accounting for the independent contributions of different muscle fibre types.

Role of vision in sighted and blind soccer players in adapting to an unstable balance task

This study tested whether a compensatory hypothesis exists on postural control during standing unstable balance tasks comparing blind soccer players (n = 7) to sighted soccer players (n = 15) and sighted sedentary individuals (n = 6). All subjects performed a pre-test, a training of ten practice trials on a single day, and a post-test balance test. All tests were performed on an unstable surface placed on a force platform and under closed-eyes conditions, and a final test was performed with open eyes. Balance performance was assessed by resultant distance (RD) and the magnitude of mean velocity (MV) of the centre of pressure (CoP) displacement, and EMG signals from the gastrocnemius lateralis, tibialis anterior, rectus femoris, and peroneus longus were measured with surface electromyography. Principal component analysis (PCA) on EMG muscular activation was used to assess EMG pattern differences during the balance tasks. All groups improved their performance, obtaining low scores for the closed-eyes condition balance task after the training period in RD, VM, and aids received to keep balance in the novel task, and no differences were found between groups or in interaction effects. Sighted individuals and the control group showed significantly lower RD and VM scores under open-eyes conditions than blind participants. As regards neuromuscular behaviour, three principal patterns explained 84.15% of the variability in the measured data. The theoretical improvement of the other senses caused by visual deprivation does not allow blind individuals to obtain better balance than sighted individuals under closed-eyes conditions, thereby reinforcing the prominent role of vision in integrating and processing the other sensory inputs. In addition, blind individuals seem to increase their muscular co-activation as a safety strategy, but this behaviour is not different to that shown by sighted people under closed-eyes conditions.

Effect of exercise-induced muscle damage on vascular function and skeletal muscle microvascular deoxygenation

This paper investigated the effects of unaccustomed eccentric exercise‐induced muscle damage (EIMD) on macro‐ and microvascular function. We tested the hypotheses that resting local and systemic endothelial‐dependent flow‐mediated dilation (FMD) and microvascular reactivity would decrease, V˙O2max would be altered, and that during ramp exercise, peripheral O₂ extraction, evaluated via near‐infrared‐derived spectroscopy (NIRS) derived deoxygenated hemoglobin + myoglobin ([HHb]), would be distorted following EIMD. In 13 participants, measurements were performed prior to (Pre) and 48 h after a bout of knee extensor eccentric exercise designed to elicit localized muscle damage (Post). Flow‐mediated dilation and postocclusive reactive hyperemic responses measured in the superficial femoral artery served as a measurement of local vascular function relative to the damaged tissue, while the brachial artery served as an index of nonlocal, systemic, vascular function. During ramp‐incremental exercise on a cycle ergometer, [HHb] and tissue saturation (TSI%) in the m. vastus lateralis were measured. Superficial femoral artery FMD significantly decreased following EIMD (pre 6.75 ± 3.89%; post 4.01 ± 2.90%; P < 0.05), while brachial artery FMD showed no change. The [HHb] and TSI% amplitudes were not different following EIMD ([HHb]: pre, 16.9 ± 4.7; post 17.7 ± 4.9; TSI%: pre, 71.0 ± 19.7; post 71.0 ± 19.7; all P > 0.05). At each progressive increase in workload (i.e., 0–100% peak), the [HHb] and TOI% responses were similar pre‐ and 48 h post‐EIMD (P > 0.05). Additionally, V˙O2max was similar at pre‐ (3.0 ± 0.67 L min⁻¹) to 48 h post (2.96 ± 0.60 L min⁻¹)‐EIMD (P > 0.05). Results suggest that moderate eccentric muscle damage leads to impaired local, but not systemic, macrovascular dysfunction.

Quantifying Achilles tendon force in vivo from ultrasound images

This study evaluated a procedure for estimating in vivo Achilles tendon (AT) force from ultrasound images. Two aspects of the procedure were tested: (i) accounting for subject-specific AT stiffness and (ii) accounting for changes in the relative electromyographic (EMG) intensities of the three triceps surae muscles. Ten cyclists pedaled at 80rpm while a comprehensive set of kinematic, kinetic, EMG, and ultrasound data were collected. Subjects were tested at four crank loads, ranging from 14 to 44Nm (115 to 370W). AT forces during cycling were estimated from AT length changes and from AT stiffness, which we derived for each subject from ultrasound data and from plantar flexion torques measured during isometric tests. AT length changes were measured by tracking the muscle-tendon junction of the medial gastrocnemius (MG) relative to its insertion on the calcaneus. Because the relative EMG intensities of the triceps surae muscles varied with load during cycling, we divided subjects׳ measured AT length changes by a scale factor, defined as the square root of the relative EMG intensity of the MG, weighted by the fractional physiological cross-sectional areas of the three muscles, to estimate force. Subjects׳ estimated AT forces during cycling increased with load (p<0.05). On average, peak forces ranged from 920±96N (14Nm, 115W) to 1510±129N (44Nm, 370W). For most subjects, ankle moments derived from the ultrasound-based AT strains were 5-12% less than the net ankle moments calculated from inverse dynamics (r²=0.71±0.28, RMSE=8.1±0.33Nm). Differences in the moments increased substantially when we did not account for changes in the muscles׳ relative EMG intensities with load or, in some subjects, when we used an average stiffness, rather than a subject-specific value. The proposed methods offer a non-invasive approach for studying in vivo muscle-tendon mechanics.