Mean Power Frequency Research Articles

Similar performance fatigability and neuromuscular responses following sustained bilateral tasks above and below critical force.

The present study examined the magnitude of performance fatigability as well as the associated limb- and intensity-specific neuromuscular patterns of responses during sustained, bilateral, isometric, leg extensions above and below critical force (CF). Twelve women completed three sustained leg extensions (1 below and 2 above CF) anchored to forces corresponding to RPE = 1, 5, and 8 (10-point scale). During each sustained leg extension, electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF) were assessed from each vastus lateralis in 5% of time-to-exhaustion (TTE) segments. Before and after each sustained leg extension, the subjects completed maximal voluntary isometric contractions (MVIC), and the percent decline was defined as performance fatigability. Polynomial regression was used to define the individual and composite neuromuscular and force values versus time relationships. Repeated-measures ANOVAs assessed differences in performance fatigability and TTE. The grand mean for performance fatigability was 10.1 ± 7.6%. For TTE, the repeated-measures ANOVA indicated that there was a significant (p < 0.05) effect for Intensity, such that RPE = 1 > 5 > 8. There were similar neuromuscular patterns of response between limbs as well as above and below CF. EMG MPF, however, exhibited decreases only above CF. Performance fatigability was unvarying above and below CF as well as between limbs. In addition, there were similar fatigue-induced motor unit activation strategies above and below CF, but peripheral fatigue likely contributed to a greater extent above CF.

The effects of Kinesiology Tape on static postural control in individuals with functional ankle instability

ObjectiveTo investigate if applying Kinesiology Tape (KT) on the unstable ankle may improve static postural control in individuals with Functional ankle instability. DesignA repeated measured study. Participants performed a series of static quiet bipedal and unipedal stances on a force platform. Measurements were taken at three different times: baseline or no tape, immediately and 24 h after the taping application with the tape remaining on the ankle. SettingA university’s psychomotor laboratory. ParticipantsTwenty young adults with Functional ankle instability aged from 18 to 30 years old. Outcome measures: Postural control was assessed by four measures derived from the centre of pressure data: Area of 95% Confidence ellipse, standard deviation of displacements, mean velocity and mean power frequency. The analysis of variance (ANOVA) was performed to determine any significant improvement in postural control over time due to KT. ResultsOnly minor changes in mean velocity and MPF in unipedal stances were observed immediately after KT application. However, the overall results indicated statistically insignificant improvements in postural control neither immediately after KT application nor after 24 h. ConclusionResults suggest that the use of KT did not affect bipedal and unipedal stances of individuals with functional ankle instability.

Human Gait Recognition Based on Multiple Feature Combination and Parameter Optimization Algorithms.

Accuracy is a key index of human gait recognition. In this paper, we propose an improved gait recognition algorithm, which combines multiple feature combination and artificial bee colony for optimizing the support vector machine (ABC-SVM). Firstly, considering the complexity characteristics of surface electromyography (sEMG) signals, four types of features are extracted from the denoised sEMG signals, including the time-domain features of integral of absolute value (IAV), variance (VAR), and number of zero-crossing (ZC) points, frequency-domain features of mean power frequency (MPF) and median frequency (MF), and wavelet features and fuzzy entropy features. Secondly, the classifiers of SVM, linear discriminant analysis (LDA), and extreme learning machine (ELM) are employed to recognize the gait with obtained features, including singe-class features, multiple combination features, and optimized features of dimension reduction by principal component analysis (PCA). Thirdly, the penalty coefficient and kernel function parameter of the SVM classifier are optimized by the ABC algorithm, and the influence of different features and classifiers on the recognition results is studied. Finally, the feature samples selected to construct the SVM classifier are trained and recognized. Results show that the classification performance of the ABC-SVM classifier is significantly better than that of the nonoptimized SVM classifier, and the average recognition rate is increased by 3.18%. In addition, the combined feature samples (time-domain, frequency-domain, wavelet, and fuzzy entropy features) not only improve the gait classification accuracy but also enhance the recognition stability.

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

PurposeThe 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.MethodsThirteen 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.ResultsThere 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%).ConclusionThe 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.

Multi-feature gait recognition with DNN based on sEMG signals.

This study proposed a gait recognition method based on the deep neural network of surface electromyography (sEMG) signals to improve the stability and accuracy of gait recognition using sEMG signals of the lower limbs. First, we determined the parameters of time domain features, including the mean of absolute value, root mean square, waveform length, the number of zero-crossing points of the sEMG signals after noise elimination, and the frequency domain features, including mean power frequency and median frequency. Second, the time domain feature and frequency domain feature were combined into a multi-feature combination. Then, the classifier was trained and used for gait recognition. Finally, in terms of the recognition rate, the classifier was compared with the support vector machine (SVM) and extreme learning machine (ELM). The results showed the method of deep neural network (DNN) had a better recognition rate than that of SVM and ELM. The experimental results of the participants indicated that the average recognition rate obtained with the method of DNN exceeded 95%. On the other hand, from the statistical results of standard deviation, the difference between subjects ranged from 0.46 to 0.94%, which also proved the robustness and stability of the proposed method.

Assessment of work-related hand and elbow workloads using measurement-based TLV for HAL

Direct-measurement-based methods for assessing workloads of the hand or elbow in the field are rare. Aim of the study was to develop such a method based on the Threshold Limit Value for Hand Activity Level (TLV for HAL). Hence, HAL was quantified using kinematic data (mean power frequencies, angular velocities and micro-pauses) and combined with electromyographic data (root-mean-square values) in order to generate a measurement-based TLV for HAL (mTLV for HAL). The multi-sensor system CUELA including inertial sensors, potentiometers and a 4-channel surface electromyography module was used. For wrist and elbow regions, associations between mTLV for HAL and disorders/complaints (quantified by odds ratios (OR [95%-confidence interval])) were tested exploratively within a cross-sectional field study with 500 participants. Higher workloads were frequently significantly associated with arthrosis of distal joints (9.23 [3.29–25.87]), wrist complaints (2.89 [1.63–5.11]) or elbow complaints (1.99 [1.08–3.67]). The new method could extend previous application possibilities.

Rehabilitation Effects of Fatigue-Controlled Treadmill Training After Stroke: A Rat Model Study.

Background: Traditional rehabilitation with uniformed intensity would ignore individual tolerance and introduce the second injury to stroke survivors due to overloaded training. However, effective control of the training intensity of different stroke survivors is still lacking. The purpose of the study was to investigate the rehabilitative effects of electromyography (EMG)-based fatigue-controlled treadmill training on rat stroke model.Methods: Sprague–Dawley rats after intracerebral hemorrhage and EMG electrode implantation surgeries were randomly distributed into three groups: the control group (CTRL, n = 11), forced training group (FOR-T, n = 11), and fatigue-controlled training group (FAT-C, n = 11). The rehabilitation interventions were delivered every day from day 2 to day 14 post-stroke. No training was delivered to the CTRL group. The rats in the FOR-T group were forced to run on the treadmill without rest. The fatigue level was monitored in the FAT-C group through the drop rate of EMG mean power frequency, and rest was applied to the rats when the fatigue level exceeded the moderate fatigue threshold. The speed and accumulated running duration were comparable in the FAT-C and the FOR-T groups. Daily evaluation of the motor functions was performed using the modified Neurological Severity Score. Running symmetry was investigated by the symmetry index of EMG bursts collected from both hind limbs during training. The expression level of neurofilament-light in the striatum was measured to evaluate the neuroplasticity.Results: The FAT-C group showed significantly lower modified Neurological Severity Score compared with the FOR-T (P ≤ 0.003) and CTRL (P ≤ 0.003) groups. The FAT-C group showed a significant increase in the symmetry of hind limbs since day 7 (P = 0.000), whereas the FOR-T group did not (P = 0.349). The FAT-C group showed a higher concentration of neurofilament-light compared to the CTRL group (P = 0.005) in the unaffected striatum and the FOR-T group (P = 0.021) in the affected striatum.Conclusion: The treadmill training with moderate fatigue level controlled was more effective in motor restoration than forced training. The fatigue-controlled physical training also demonstrated positive effects in the striatum neuroplasticity. This study indicated that protocol with individual fatigue-controlled training should be considered in both animal and clinical studies for better stroke rehabilitation.

Calibrating ratings of perceived fatigue relative to objective measures of localised muscle fatigue using a feedback-based familiarisation protocol

Localized muscle fatigue (LMF) manifests as a reduction in muscle force generating capacity, an increase in electromyography signal amplitude and a decrease in mean power frequency (MnPF). Estimates of LMF can also be obtained subjectively through ratings of perceived fatigue (RPF); however, the provision of RPF scale familiarisation is inconsistent within the literature. The purpose of this study was to explore the effect of an RPF familiarisation session on the accuracy of RPF, relative to objective measures of fatigue, during a LMF protocol. Twenty participants performed intermittent isometric elbow flexion efforts to fatigue. Following each 5-minute cycle, RPF ratings were provided using a visual analog scale, and an MVC was obtained. On day 2, the ‘feedback’ group received visual feedback pertaining to their reduction in MVC, immediately following their RPF input, while the control group received no feedback. On day 3 (retention), RMSE was 72% lower between RPF and MVC, and 69% lower between RPF and MnPF for the feedback group after the familiarisation period. Findings support the inclusion of a familiarisation session to improve RPF as a surrogate measure for traditional objective measures of LMF.

Intervention with thumbtack needling on spinal low back pain in Air Force crew: a randomized controlled trial

To observe the clinical effect on spinal low back pain (SLBP) in Air Force crew treated with novel thumbtack needling therapy and to analyze the relevant factors of the therapeutic effect. A total of 120 Air Force crew with SLBP were randomized into a thumbtack needling group (40 cases), an external treatment group (40 cases, 1 case dropped off ) and a combined treatment group (40 cases, 1 case dropped off ). In the thumbtack needling group, the thumbtack needling therapy was adopted. The novel thumbtack needles were inserted at the lower No.6 region of the wrist-ankle acupuncture, Yaotongdian (EX-UE 7), Yaoyangguan (GV 3), etc. Each point was pressed and kneaded for 1 min each time, 3 or 4 times a day. The treatment for 3 days was taken as one course. At the interval of 2 days, 3 courses were required totally. In the external treatment group, shangshi zhitong plaster was compressed on the center of the tender site in the lumbar region, once daily, consecutively for 6 days as one course. At an interval of 1 day, 2 courses were required totally. In the combined treatment group, the treatments in the thumbtack needling group and the external treatment group were used in combination. Before and after treatment, McGill score and the score of Oswestry dysfunction index (ODI) were compared in the patients among the three groups. The average EMG (AEMG) and the mean power frequency (MPF) were analyzed by using JE-TB0810 electromyography (EMG) acquisition system to evaluate the erector spinae tension in the patients before and after treatment. The clinical effect was observed in the patient of each group and the safety was evaluated. Logistic analysis was performed on the relevant factors of therapeutic effect in the patients. Compared with the values before treatment, McGill scores and ODI scores were reduced (P<0.05), and AEMG and MPF increased in the patients of each group after treatment (P<0.05). After treatment, McGill scores and ODI scores in the thumbtack needling group and the combined treatment group were lower than those in the external treatment group (P<0.05), and AEMG and MPF were higher than the external treatment group (P<0.05). The total effective rates were 87.5% (35/40) and 87.2% (34/39) in the thumbtack needling group and the combined treatment group respectively and were higher than 64.1% (25/39) in the external treatment group (P<0.05). The incidence of the adverse reaction in the combined treatment group was higher than the other two groups (P<0.05). The weekly exercise frequency was the independent factor of the therapeutic effect (OR =12.166, P<0.001). The thumbtack needling therapy is significantly effective on spinal low back pain in Air Force crew and is of the safety. Hence, this therapy is applicable to be promoted in the primary care army hospital.

Interlimb Neuromuscular Responses During Fatiguing, Bilateral, Leg Extension Exercise at a Moderate Versus High Load.

This study determined the load- and limb-dependent neuromuscular responses to fatiguing, bilateral, leg extension exercise performed at a moderate (50% one-repetition maximum [1RM]) and high load (80% 1RM). Twelve subjects completed 1RM testing for the bilateral leg extension, followed by repetitions to failure at 50% and 80% 1RM, on separate days. During all visits, the electromyographic (EMG) and mechanomyographic (MMG), amplitude (AMP) and mean power frequency (MPF) signals were recorded from the vastus lateralis of both limbs. There were no limb-dependent responses for any of the neuromuscular signals and no load-dependent responses for EMG AMP, MMG AMP, or MMG MPF (p = .301-.757), but there were main effects for time that indicated increases in EMG and MMG AMP and decreases in MMG MPF. There was a load-dependent decrease in EMG MPF over time (p = .032) that suggested variability in the mechanism responsible for metabolite accumulation at moderate versus high loads. These findings suggested that common drive from the central nervous system was used to modulate force during bilateral leg extension performed at moderate and high loads.

Muscular fatigue measurements for push‐down tasks in ground demolitions

AbstractDemolition hammering tasks are physically demanding tasks that could cause muscle fatigue and musculoskeletal disorders. Electromyography (EMG) data have been adopted to assess levels of muscular activity and onset of muscular fatigue for both industrial tasks and physical activities. An experiment simulating a manual demolition task on the ground was performed on 23 healthy male participants. The objectives were to test the hypotheses that the handle height and the force applied to affect the EMG amplitude, the increase of the EMG amplitude, and the decline of the mean power frequency (MPF) of the EMG for performing the tasks. This study also aimed at finding the most fatigued muscles which dominate the end of the sustained push‐down tasks in ground demolitions. The results showed that the EMG amplitude required to perform the tasks was significantly affected by the handle height and force applied. Significant increases in EMG amplitude and decreases in MPF were found. Bicep brachii, tricep brachii, and pectoralis major muscles were the most fatigued muscles that dominated the termination of the tasks. Pushing with body leaning forward to utilize partial body weight was less fatiguing than the other two postures. Elbow flexion is undesirable and should be avoided when performing such tasks.

Parametric Study of Changes in Human Balancing Skill by Repeated Balancing Trials on Rolling Balance Board

Dynamic balance conditions were realized by asking eight volunteers to stand on uniaxial balance board with adjustable geometry and to carry out 60 s long balancing trials. Four different balance board geometry were used, each associated with different difficulty level. Balancing trials were repeated five times weekly (learning period) in order to test improvement of balancing skill. The measurement was repeated eight weeks after the learning period in order to check the persistence of the balancing skill (confirmation session). Oscillations of ankle angle and hip angle were monitored by OptiTrack motion capture system and four stabilometry parameters were used to characterize improvement in balancing performance, namely, Standard Deviation (STD), Largest Amplitude (LA), Normalized Path Length (NPL) and Mean Power Frequency (MPF). STD and NPL show similar tendency to the preliminary expectations, therefore they can be considered as good measures to describe balancing performance. Results show that subjects used ankle strategy for the less difficult balance board configurations, while for the more difficult tasks, hip strategy was also involved. Changes in STD and NPL during the learning period showed that the improvement and the persistence in balancing skill is more significant for more difficult balancing tasks.

Day to Day Consistency and Inter-subject Variability of Neuromuscular Responses and Performance Fatigability as the Result of Maximal, Bilateral, Dynamic Leg Extensions

The purpose of the present study was to examine the day-to-day consistency and inter-subject variability of composite and individual, neuromuscular and torque patterns of responses as a result of a fatiguing bout of maximal, bilateral, isokinetic leg extension muscle actions. Ten men (Mean ± SD = 21.6 ± 2.5 years) completed two testing visits consisting of pretest and posttest maximal voluntary isometric contractions (MVIC) as well as 25 maximal, bilateral, isokinetic (180°/s), leg extension muscle actions. Electromyographic (EMG) and mechanomyographic (MMG) signals were collected from the vastus lateralis and normalized to the MVIC. Performance fatigability was defined as the percent decline in torque between the average of repetitions 1, 2, and 3 and repetitions 23, 24, and 25. Polynomial regression was used to examine the individual and composite relationships between EMG amplitude (AMP), EMG mean power frequency (MPF), MMG AMP, MMG MPF, and torque versus repetitions. There was no significant difference (d = 0.80; P = 0.17) in the performance fatigability between Day 1 (19.3% ± 7.1%) and Day 2 (26.9% ± 11.3%). Polynomial regression indicated substantial inter-subject variability, but high day-to-day consistency. The composite EMG AMP, MMG AMP, and MMG MPF patterns of responses demonstrated consistency across days. The composite EMG MPF patterns of responses, however, were not consistent between Day 1 and Day 2. In addition, based on the high inter-subject variability, future studies should present both composite patterns of neuromuscular responses and the patterns of responses on a subject-by-subject basis to make inferences regarding fatigue-induced changes in motor unit activation strategies.

Exploring Localized Muscle Fatigue Responses at Current Upper-Extremity Ergonomics Threshold Limit Values.

The purpose of this study was to evaluate localized muscle fatigue responses at three upper-extremity ergonomics threshold limit value (TLV) duty cycles. Recently, a TLV equation was published to help mitigate excessive development of localized muscle fatigue in repetitive upper limb tasks. This equation predicts acceptable levels of maximal voluntary contraction (% MVC) for a given duty cycle (DC). Experimental validation of this TLV curve has not yet been reported, which can help guide utilization by practitioners. Eighteen participants performed intermittent isometric elbow flexion efforts, in three separate counter-balanced sessions, at workloads defined by the American Conference of Governmental Industrial Hygenists' (ACGIH) TLV equation: low DC (20% DC, 29.6% MVC), medium DC (40% DC, 19.7% MVC), and high DC (60% DC, 13.9% MVC). Targeted localized muscle fatigue (LMF) of the biceps brachii was tracked across numerous response variables, including decline in strength (MVC), electromyography (EMG) amplitude and mean power frequency (MnPF), and several psychophysical ratings. At task completion, biceps MnPF and MVC (strength) were significantly different between each TLV workload, with the high DC condition eliciting the largest declines in MnPF and MVC. Findings demonstrate that working at different DCs along the ACGIH TLV curve may not be equivalent in preventing excessive LMF. Higher DC workloads elicited a greater LMF response across several response variables. High DC work of the upper extremity should be avoided to mitigate excess LMF development. Current TLVs for repetitive upper-extremity work may overestimate acceptable relative contraction thresholds, particularly at higher duty cycles.

The Effect of Unilateral Vestibular Loss on Standing Balance During Postural Threat.

Vestibular deficit patients have an increased fall risk and fear of falling. Postural threat, known to increase balance-related fear and anxiety, influences vestibular gains during quiet standing in young healthy adults. The current study examined whether there is a similar relationship for peripheral unilateral vestibular loss (UVL) patients in comparison to age-matched healthy controls (HC). University laboratory. Prospective laboratory study. Eleven UVL patients, nine with vestibular neurectomy. Eleven aged-matched HCs. Subjects stood on a hydraulic lift placed at two heights: low (0.8 m, away from the edge) and high (3.2 m, at the edge). Amplitude (root mean square), mean power frequency (MPF), and mean position were analyzed for center of foot pressure (COP) and 90% ranges for angle amplitude and velocity for trunk sway. Group interactions were strongest for anterior-posterior (AP) COP and trunk pitch angle. AP lean away from the edge was greater in HCs than UVLs. HCs, but not UVLs had a decrease in root mean square AP COP with height. Trunk pitch sway was changed similarly. Both groups had increased trunk pitch velocity at height. Changes with height were less for roll: MPF of lateral COP increased with height for UVLs with no changes for HCs, and trunk roll amplitude decreased for both groups. This report provides evidence for a differential effect of height induced postural threat on balance control between UVLs and HCs presumably due to the reduced vestibular-spinal gain in UVL subjects.

The influence of muscle fiber type on slow component of oxygen uptake kinetics

The purpose of this study was to investigate the influence of muscle fiber type on the slow component of oxygen uptake (VO2) kinetics and electromyographic activity. Twelve sprinters and ten endurance runners participated in the study. They performed two separate treadmill running tests, the first test being conducted to determine the ventilatory threshold and maximal oxygen uptake. The second test consisted of a 6 min running bout at severe exercise intensity. A two-component exponential model was used to fit the VO2 response. Surface electromyographic signals were collected from Vastus lateralis, and processed by wavelet analysis. Sprinters and endurance runners, with their distinct anaerobic and aerobic fitness, showed a substantial difference in VO2 slow component during severe exercise. The sprinters showed a significantly higher VO2 slow component amplitude (A2: 381.0 ± 96.3 mL/min) and a significantly earlier slow component onset (TD2: 118.1 ± 16.1 s) than the endurance runners (A2: 142.2 ± 58.4 mL/min, TD2: 145.9 ± 19.9 s). The electromyographic mean power frequency of the tested muscles increased significantly during the slow component phase. There is a significant correlation between VO2 slow component and electromyographic mean power frequency for endurance runners ( r = 0.50, p = 0.003). The combined use of VO2 kinetics modeling and electromyographic measurement provides evidence of the influence of muscle fiber type on slow component of oxygen uptake kinetics during severe intensity exercise.

Different sEMG and EEG Features Analysis for Gait phase Recognition.

This research focuses on the gait phase recognition using different sEMG and EEG features. Seven healthy volunteers, 23-26 years old, were enrolled in this experiment. Seven phases of gait were divided by three-dimensional trajectory of lower limbs during treadmill walking and classified by Library for Support Vector Machines (LIBSVM). These gait phases include loading response, mid-stance, terminal Stance, pre-swing, initial swing, mid-swing, and terminal swing. Different sEMG and EEG features were assessed in this study. Gait phases of three kinds of walking speed were analyzed. Results showed that the slope sign change (SSC) and mean power frequency (MPF) of sEMG signals and SSC of EEG signals achieved higher accuracy of gait phase recognition than other features, and the accuracy are 95.58% (1.4 km/h), 97.63% (2.0 km/h) and 98.10% (2.6 km/h) respectively. Furthermore, the accuracy of gait phase recognition in the speed of 2.6 km/h is better than other walking speeds.

A Novel Quantitative Spasticity Evaluation Method Based on Surface Electromyogram Signals and Adaptive Neuro Fuzzy Inference System.

Stroke patients often suffer from spasticity. Before treatment of spasticity, there are often practical demands for objective and quantitative assessment of muscle spasticity. However, the common quantitative spasticity assessment method, the tonic stretch reflex threshold (TSRT), is time-consuming and complicated to implement due to the requirement of multiple passive stretches. To evaluate spasticity conveniently, a novel spasticity evaluation method based on surface electromyogram (sEMG) signals and adaptive neuro fuzzy inference system (i.e., the sEMG-ANFIS method) was presented in this paper. Eleven stroke patients with spasticity and four healthy subjects were recruited to participate in the experiment. During the experiment, the Modified Ashworth scale (MAS) scores of each subject was obtained and sEMG signals from four elbow flexors or extensors were collected from several times (4–5) repetitions of passive stretching. Four time-domain features (root mean square, the zero-cross rate, the wavelength and a 4th-order autoregressive model coefficient) and one frequency-domain feature (the mean power frequency) were extracted from the collected sEMG signals to reflect the spasticity information. Using the ANFIS classifier, excellent regression performance was achieved [mean accuracy = 0.96, mean root-mean-square error (RMSE) = 0.13], outperforming the classical TSRT method (accuracy = 0.88, RMSE = 0.28). The results showed that the sEMG-ANFIS method not only has higher accuracy but also is convenient to implement by requiring fewer repetitions (4–5) of passive stretches. The sEMG-ANFIS method can help stroke patients develop proper rehabilitation training programs and can potentially be used to provide therapeutic feedback for some new spasticity interventions, such as shockwave therapy and repetitive transcranial magnetic stimulation.

The effects of hypoxia on muscle deoxygenation and recruitment in the flexor digitorum superficialis during submaximal intermittent handgrip exercise

BackgroundDecreased oxygenation of muscle may be accentuated during exercise at high altitude. Monitoring the oxygen saturation of muscle (SmO2) during hand grip exercise using near infrared spectroscopy during acute exposure to hypoxia could provide a model for a test of muscle performance without the competing cardiovascular stresses that occur during a cycle ergometer or treadmill test. The purpose of this study was to examine and compare acute exposure to normobaric hypoxia versus normoxia on deoxygenation and recruitment of the flexor digitorum superficialis (FDS) during submaximal intermittent handgrip exercise (HGE) in healthy adults.MethodsTwenty subjects (11 M/9 F) performed HGE at 50% of maximum voluntary contraction, with a duty cycle of 2 s:1 s until task failure on two occasions one week apart, randomly assigned to normobaric hypoxia (FiO2 = 12%) or normoxia (FiO2 = 21%). Near-infrared spectroscopy monitored SmO2, oxygenated (O2Hb), deoxygenated (HHb), and total hemoglobin (tHb) over the FDS. Surface electromyography derived root mean square and mean power frequency of the FDS.ResultsHypoxic compared to normoxic HGE induced a lower FDS SmO2 (63.8 ± 2.2 vs. 69.0 ± 1.5, p = 0.001) and both protocols decreased FDS SmO2 from baseline to task failure. FDS mean power frequency was lower during hypoxic compared to normoxic HGE (64.0 ± 1.4 vs. 68.2 ± 2.0 Hz, p = 0.04) and both decreased mean power frequency from the first contractions to task failure (p = 0.000). Under both hypoxia and normoxia, HHb, tHb and root mean square increased from baseline to task failure whereas O2Hb decreased and then increased during HGE. Arterial oxygen saturation via pulse oximetry (SpO2) was lower during hypoxia compared to normoxia conditions (p = 0.000) and heart rate and diastolic blood pressure only demonstrated small increases. Task durations and the tension-time index of HGE did not differ between normoxic and hypoxic trials.ConclusionHypoxic compared to normoxic HGE decreased SmO2 and induced lower mean power frequency in the FDS, during repetitive hand grip exercise however did not result in differences in task durations or tension-time indices. The fiber type composition of FDS, and high duty cycle and intensity may have contributed greater dependence on anaerobiosis.

Thermoregulation and shivering responses in elite alpine skiers

ABSTRACT This study aimed to characterise the thermoregulatory responses of elite alpine skiers. Core (gastro-intestinal) and skin temperatures were recorded continuously from 4 national team skiers representing 18 training-sessions for a total of 83 ski runs (average ambient temperature 1.9°C). Shivering responses were estimated from quadriceps and hamstrings EMG recordings during 77 chairlifts. Temperature responses were also obtained from 6 accompanying staffs representing 16 training-sessions (passive in 10 cases, following the skiers in 6 cases). Core temperature of the skiers (P < .001) but not the staff (P = .103) increased during training and was higher in skiers than staff after one-third of the training session (P < .006). Conversely, average skin temperature of the skiers decreased during training (P < .001) and was lower in skiers than staff for the second half of the training. Muscle activity during chairlifts remained below 1% and there was no meaningful shivering. Muscle activity decreased whilst mean and median power frequency increased during the chairlift (P < .020). Muscle activity was also lower during the last lift than the first one whilst mean and median power frequency were higher (P < .020). In conclusion, skin temperature decreased during Slalom and Giant Slalom in elite alpine skiers, likely due to the limited insulative capacity of the racing suit and the high velocity increasing convective heat loss. Conversely, core temperature increased during the training session suggesting that the metabolic heat production was larger than the convective heat loss, and was also sufficient to maintain homeostasis without shivering.