Peak Electromyography Research Articles

An Acute Bout of Static Stretching Does Not Affect Maximal Eccentric Isokinetic Peak Torque, the Joint Angle at Peak Torque, Mean Power, Electromyography, or Mechanomyography

An Acute Bout of Static Stretching Does Not Affect Maximal Eccentric Isokinetic Peak Torque, the Joint Angle at Peak Torque, Mean Power, Electromyography, or Mechanomyography

Trial-by-Trial Analysis or Averaging

The control of human limb movement has been the focus of research for more than a century. A major issue to emerge from this work is the manner in which the central nervous system regulates electromyographic (EMG) activity to produce movements that differ in distance, velocity, and movement time. However, the different methods of analysis often used to analyze EMG data could result in different kinematic-EMG relationships. In this study, participants performed an elbow flexion task to one of five distance goals (between 5° and 50°) using three movement speeds. EMG data from the right elbow flexors were compared using a trial-by-trial analysis and one based on averaged data. Averaging across trials underestimated biceps EMG amplitude at all movement distances and speeds compared to a trial-by-trial analysis. Averaging overestimated EMG burst duration compared to the trial-by-trial analysis. Peak agonist EMG amplitude was positively related to distance and inversely related to movement time. Agonist EMG duration was constant for movement distances less than 30° but increased in the 50° condition. The results support the view that peak EMG amplitude and duration can be controlled independently, but EMG duration changes only for longer distance movements when additional force is required.

Isokinetic and electromyographic study of internal and external rotator muscles of tennis player

The purpose of this study was to explore the effects of intensive tennis practice on the mechanical and electromyographic (EMG) activity of the external (ER) and internal (IR) rotators of the shoulder. Isokinetic and EMG testing of tennis (T, N = 8) and control (C, N = 8) subjects was performed using a CYBEX NORM. Shoulder rotation strength was measured at 5 angular velocities: concentric 60, 180, 300 and eccentric 60 and 180 ◦ /s during which peak torque (PT) and EMG activity of the infraspinatus (ER) and pectoralis major (IR) was recorded. For the T group dominant side (DS) the ER/IR ratio was lower than the non dominant side (NDS) whereas no such difference was observed between DS and NDS of C group. No ERecc/IRcon ratio difference was observed between sides and groups. ER co-activation in the T group was greater in the DS compared to the NDS and the DS of C group, while values were the same for both sides of C group. It therefore seems that tennis players present an adaptation to their activity. However their mechanical and EMG values deviate quite sharply from standard values which may potentially account for injury.

Robust source analysis of oscillatory motor cortex activity with inherently variable phase delay

This study evaluated quantitatively the synchronization between the magnetoencephalography (MEG) and electromyography (EMG) signals and developed a novel method for the determination of the synchronization in order to increase the reliability of the source analysis of the oscillatory motor cortex activity. The new method is based on our observation that there are large variances in the time lag due to relatively low muscle-cortex synchronization which reduces the signal-to-noise ratio of the MEG signal when averaged in direct synchrony with the rectified EMG peaks. To improve the localization of the motor cortex activity, time-frequency analysis was performed for each epoch coinciding with an EMG peak to reject the weak oscillatory activity and artifacts. In addition, the MEG signals were shifted to maximize the coherence between MEG and rectified EMG by determining for each accepted epoch the time lag resulting in a maximum cross-correlation. An experiment was carried out using 30 subjects in order to determine the applicability of this method to a real situation. The synchronization and the results of the corresponding source analysis based on the novel method were compared with the data obtained using the non-phase-shift method and Hilbert approach detecting EMG phase. The results showed that the synchronization was significantly enhanced and the signal-to-noise ratio of the MEG signals improved, and that the localized dipoles of all subjects were well clustered at the motor cortex. This method, based on shifting the MEG epochs according to the simultaneously measured time lag, considerably improves the performance of the averaging and localization of the rhythmic activity of the motor cortex.

EMG normalization to study muscle activation in cycling

The value of electromyography (EMG) is sensitive to many physiological and non-physiological factors. The purpose of the present study was to determine if the torque–velocity test (T–V) can be used to normalize EMG signals into a framework of biological significance. Peak EMG amplitude of gluteus maximus (GMAX), vastus lateralis (VL), rectus femoris (RF), biceps femoris long head (BF), gastrocnemius medialis (GAS) and soleus (SOL) was calculated for nine subjects during isometric maximal voluntary contractions (IMVC) and torque–velocity bicycling tests (T–V). Then, the reference EMG signals obtained from IMVC and T–V bicycling tests were used to normalize the amplitude of the EMG signals collected for 15 different submaximal pedaling conditions. The results of this study showed that the repeatability of the measurements between IMVC (from 10% to 23%) and T–V (from 8% to 20%) was comparable. The amplitude of the peak EMG of VL was 99 ± 43% higher ( p < 0.001) when measured during T–V. Moreover, the inter-individual variability of the EMG patterns calculated for submaximal cycling exercises differed significantly when using T–V bicycling normalization method (GMAX: 0.33 ± 0.16 vs. 1.09 ± 0.04, VL: 0.07 ± 0.02 vs. 0.64 ± 0.14, SOL: 0.07 ± 0.03 vs. 1.00 ± 0.07, RF: 1.21 ± 0.20 vs. 0.92 ± 0.13, BF: 1.47 ± 0.47 vs. 0.84 ± 0.11). It was concluded that T–V bicycling test offers the advantage to be less time and energy-consuming and to be as repeatable as IMVC tests to measure peak EMG amplitude. Furthermore, this normalization method avoids the impact of non-physiological factors on the amplitude of the EMG signals so that it allows quantifying better the activation level of lower limb muscles and the variability of the EMG patterns during submaximal bicycling exercises.

The Effect Of Cadence On Muscle Recruitment In Triathletes

PURPOSE We have previously reported that cycling muscle recruitment is less skilled in triathletes than cyclists with similar cycling training loads. This study investigated the relationship between muscle recruitment and cadence in triathletes, which may provide further evidence of less skilled movement control. METHODS: Participants were eight elite triathletes. Comparisons were made with data from our earlier study of nine elite and ten novice cyclists. Electromyographic (EMG) recordings were made using indwelling electrodes from tibialis anterior (TA), tibialis posterior (TP), peroneus longus (PL), gastrocnemius lateralis (GL) and soleus (SOL). Cycling at individual preferred cadence (PC), 55–60, 75–80 and 90–95 rpm were investigated in random order. Cycling trials were conducted on each participant's bike secured on a magnetic trainer. Cycling intensity was controlled using ratings of perceived exertion (RPE). RESULTS The increase in cadence from 57.5 to 92.5 rpm was associated with a decrease in modulation of muscle activity (i.e. longer bursts of activity and a higher level of activity between main bursts) in triathletes for TA, SOL (p 0.56). Coactivation increased with cadence in triathletes in proportion to increased duration of primary muscle activity, as it did in novice cyclists. Peak EMG amplitude increased with cadence in triathletes and was not minimized at PC (p = 0.21), which is consistent with our findings in novice and elite cyclists. Times of peak EMG activity and variability of muscle recruitment were not influenced by cadence in any group (p > 0.32). CONCLUSION PC is not related to peak EMG amplitude in triathletes, which is consistent with our findings in novice and elite cyclists. Less modulation of muscle activity and greater muscle coactivation with increased in cadence in triathletes is considered as further evidence of less skilled control of the movement relative to cyclists with similar cycling training loads.

Electromyographic analysis of the rider's muscles at trot

The aim of this study was to investigate rider muscle activity in relation to horse movement. Electromyographic (EMG) activity of 12 upper-body muscles was recorded simultaneously with the horse's footfall timing for six riders, riding the same horse at trot. Data for five strides were analysed for each rider. Rectus abdominis, upper trapezius, middle trapezius, flexor carpi radialis, biceps brachii, triceps brachii and middle deltoid muscles had constant patterns with two peaks occurring in the same phase of the stride in all riders. Peak EMG values in the upper trapezius and middle trapezius occurred in early stance, and were considered to stabilize the rider's neck and scapula during impact of the diagonal limbs. The rectus abdominis showed peak EMG activity in mid-stance to stabilize the trunk and enable the rider to follow the horse's movement by swinging the pelvis forward as the horse's body reversed direction from downward to upward motion. The triceps brachii, which was active during late stance, and the biceps brachii, which was activated early in stance, stabilized the rider's hands and maintained contact with the bit. Teres major, extensor carpi ulnaris and serratus anterior muscles had a small range of activity (33, 26 and 37%, respectively), consistent with tonic activation or were inactive, suggesting that their function may be related to general postural control.

Patterns of leg muscle recruitment vary between novice and highly trained cyclists

This study compared patterns of leg muscle recruitment and coactivation, and the relationship between muscle recruitment, coactivation and cadence, in novice and highly trained cyclists. Electromyographic (EMG) activity of tibialis anterior (TA), tibialis posterior (TP), peroneus longus (PL), gastrocnemius lateralis (GL) and soleus (SOL) was recorded using intramuscular fine-wire electrodes. Four experimental conditions of varying cadence were investigated. Differences were evident between novice and highly trained cyclists in the recruitment of all muscles. Novice cyclists were characterized by greater individual variance, greater population variance, more extensive and more variable muscle coactivation, and greater EMG amplitude in periods between primary EMG bursts. Peak EMG amplitude increased linearly with cadence and was not different at individual preferred cadence in either novice or highly trained cyclists. However, EMG amplitude in periods between primary EMG bursts, as well as the duration of primary EMG bursts, increased with increasing cadence in novice cyclists but were not influenced by cadence in highly trained cyclists. Our findings suggest that muscle recruitment is highly skilled in highly trained cyclists and less refined in novice cyclists. More skilled muscle recruitment in highly trained cyclists is likely a result of neuromuscular adaptations due to repeated performance of the cycling movement in training and competition.

A pilot study of the initial effects of anti-pronation taping on electromyographic activity of lower leg muscles during walking

Clinicians frequently use anti-pronation (AP) taping to relieve symptoms and improve function in the management of musculoskeletal pain and injury, yet the mechanisms behind this effect have not been fully explored. To date, the majority of the literature has focused on the mechanical effects of AP taping and little has been done to explore its possible neurophysiological effects. This pilot study set out to investigate the effect of the Augmented LowDye taping technique on the electromyographic (EMG) activity of muscles of the lower leg during walking. Five asymptomatic subjects, who exhibited clinically abnormal pronation during a visual assessment of gait, walked on a treadmill for ten minutes before and after the application of the taping technique. Bipolar intra-muscular electrodes were used to record the EMG of the tibialis anterior (TA), tibialis posterior (TP), gastrocnemius (GN) and peroneus longus (PL) during walking. A two-way repeated measures analysis of variance was used to compare the EMG activity (peak amplitudes, duration of activity) for each muscle. The co-efficient of multiple correlations was calculated to evaluate the variability of muscle recruitment patterns within each subject. Visual comparisons of EMG activity during individual walking strides before and after the application of tape were also performed. Peak EMG activity decreased by 25% in TA and by 45% in TP following the application of tape. There were no significant differences in peak EMG activity of GN or PL, or in duration of EMG activity for any muscle. Results from this study suggest that neurophysiological changes could contribute to the mechanism behind AP taping.

Effects of Repeated Treadmill Walks on Lower Limb Antagonist Muscle Co-activation in Cerebral Palsy

To ensure that results from a treadmill walking protocol do not simply reflect learning, subjects must be habituated to walking on a treadmill. PURPOSE: To determine, for children and adolescents with mild cerebral palsy (CP), if: i) lower limb antagonist muscle co-activation during treadmill walking is affected by repeated walking bouts on different days, and ii) the effects of repeated walking bouts vary according to walking speed, co-activation site (thigh or lower leg) or lower limb dominance. METHODS: Following 12–15 minutes of treadmill walking practice during an introductory visit, 3 girls and 5 boys (11.9 ± 2.5 y) with mild spastic CP (n=5 diplegic CP, n=3 hemiplegic CP) walked on a treadmill for 3 minutes at three different speeds; 60, 75, and 90% of their previously determined fastest treadmill walking speed (FWS), on three different days. Electromyographic (EMG) activity for antagonist muscles at the thigh (quadriceps and hamstrings) and at the lower leg (tibialis anterior and triceps surae), bilaterally, was collected for the entire 3 minutes of each walk. Antagonist muscle co-activation at the thigh and lower leg was subsequently quantified using a co-activation measure (CM, where 100 = peak EMG activity). RESULTS: Repeated treadmill walks on different days did not affect the CM at any site, or at any speed. Independent of day, speed, and lower limb dominance, the thigh CM was on average 20% higher (P = 0.02) than the lower leg CM. There was also a trend (P = 0.06) for co-activation to be on average 16% higher for the non-dominant compared to the dominant leg, independent of the day, speed or site. Between-day reliability of the CM was high (intraclass correlation coefficient, R = .99). Variability (co-efficient of variation) of the CM was greatest for the dominant thigh (13.8%) and least for the non-DOM thigh (9.2%). CONCLUSIONS: An initial treadmill walking practice session of 12–15 minutes may be sufficient for obtaining stable and reliable between-day lower limb CM values. Stability of CM with this walking practice protocol is further suggested by the similarity of the present inter-site and inter-dominance patterns, across days and across speeds, to previous findings which used the same treadmill walking practise protocol, for one speed (90% FWS), on one day.

Effects of treadmill inclination and speed on forelimb muscle activity and kinematics in the horse

AbstractThe study aimed to investigate the effect of speed and incline on EMG activity in thebrachiocephalicusmuscle and the long and lateral heads of thetriceps brachiimuscle. Six horses were exercised on a treadmill at walk (1.7 m s-1), trot (4.0 m s-1) and right lead canter (7.2 m s-1) on a 0 and 8% incline. Kinematics (120 Hz) and electromyography (EMG) (2000 Hz) data were collected simultaneously from the left forelimb of each horse. Significant differences in relation to velocity and incline were identified using two-way ANOVA andpost hocStudent–Newman–Keuls tests (P≪0.05). The degree of association between timing of peak EMG intensity and the timing of maximum protraction/retraction angles was assessed using ANCOVA. Increases in velocity led to an increase in stride length and reduction in stride duration. Exercise on the incline increased stance duration and decreased swing duration, while limb protraction/retraction increased. The time of peak EMG activity in thebrachiocephalicuswas highly related to time of maximum limb retraction (r2=0.84). The time of peak EMG activity in the long head of thetriceps brachiiwas highly associated with time of maximum limb protraction (r2=0.87). Increases in velocity and incline both caused an increase in the intensity of the EMG signal from each muscle. Duration of EMG activity was prolonged in the long head of thetriceps brachiimuscle and in thebrachiocephalicusmuscle as velocity increased. Treadmill speed and slope therefore both alter the workload placed on forelimb muscles.

Leg muscle recruitment in highly trained cyclists

In this study, we examined patterns of leg muscle recruitment and co-activation, and the relationship between muscle recruitment and cadence, in highly trained cyclists. Electromyographic (EMG) activity of the tibialis anterior, tibialis posterior, peroneus longus, gastrocnemius lateralis and soleus was recorded using intramuscular electrodes, at individual preferred cadence, 57.5, 77.5 and 92.5 rev · min−1. The influence of electrode type and location on recorded EMG was also investigated using surface and dual intramuscular recordings. Muscle recruitment patterns varied from those previously reported, but there was little variation in muscle recruitment between these highly trained cyclists. The tibialis posterior, peroneus longus and soleus were recruited in a single, short burst of activity during the downstroke. The tibialis anterior and gastrocnemius lateralis were recruited in a biphasic and alternating manner. Contrary to existing hypotheses, our results indicate little co-activation between the tibialis posterior and peroneus longus. Peak EMG amplitude increased linearly with cadence and did not decrease at individual preferred cadence. There was little variation in patterns of muscle recruitment or co-activation with changes in cadence. Intramuscular electrode location had little influence on recorded EMG. There were significant differences between surface and intramuscular recordings from the tibialis anterior and gastrocnemius lateralis, which may explain differences between our findings and those of previous studies.

Surface EMG of jaw‐elevator muscles and chewing pattern in complete denture wearers

The aim of this study was to investigate the adaptation process of masticatory patterns to a new complete denture in edentulous subjects. For this purpose, muscle activity and kinematic parameters of the chewing pattern were simultaneously assessed in seven patients with complete maxillary and mandibular denture. The patients were analysed (i) with the old denture, (ii) with the new denture at the delivery, (iii) after 1 month and (iv) after 3 months from the delivery of the new denture. Surface electromyographic (EMG) signals were recorded from the masseter and temporalis anterior muscles of both sides and jaw movements were tracked measuring the motion of a tiny magnet attached at the lower inter-incisor point. The subjects were asked to chew a bolus on the right and left side. At the delivery of the new denture, peak EMG amplitude of the masseter of the side of the bolus was lower than with the old denture and the masseters of the two sides showed the same intensity of EMG activity, contrary to the case with the old denture. EMG amplitude and asymmetry of the two masseter activities returned as with the old denture in 3 months. The EMG activity in the temporalis anterior was larger with the old denture than in the other conditions. The chewing cycle width and lateral excursion decreased at the delivery of the new denture and recovered after 3 months.

The reproducibility of peak isokinetic torque and EMG activity in unfamiliarised subjects on repeated days

The aim of this investigation was to examine the intra-subject and group reproducibility of isokinetic muscle function testing and the associated surface electromyography (EMG) signal on repeated days testing. Fifteen subjects who were unfamiliar with isokinetic dynamometry completed maximal isokinetic elbow flexor contractions at 60 ◦ /s and 210 ◦ /s on five consecutive days. Surface electromyography was recorded from the biceps brachii to examine the electrical activity associated with the peak torque. The intra-subject reproducibility was moderate for isokinetic torque: mean coefficient of variation (CV) of 8.93% at 60 ◦ /s and 9.14% at 210 ◦ /s, however the EMG and EMG:torque ratio were somewhat more variable: mean CV of 15.18% and 18.42% at 60 ◦ /s, respectively and 11.97% and 14.50% at 210 ◦ /s, respectively. The group reproducibility for all variables at both isokinetic speeds were high with intraclass correlation coefficients ranging from 0.92 and 0.99. In addition, the group CV for isokinetic peak torque, EMG and EMG:torque ratio for both contraction speeds ranged from 1.47% to 5.12%. These results illustrate that individual subjects can show large day-to-day variations in torque and EMG, however when group data are examined, both torque and the associated EMG activity demonstrate high reproducibility. Practitioners should therefore express caution when interpreting longitudinal changes in an individual's isokinetic data.

Long-term repeatability of force, endurance time and muscle activity during isometric contractions

We determined the repeatability and correlations between force, endurance and muscle activity during isometric contractions over three years. Twenty-six subjects, with and without complaints of the shoulder and neck, performed standardized maximal and submaximal shoulder-abduction contractions and wrist extension-contractions at yearly intervals from 1997 to 1999. Peak forces developed during maximal contraction and the endurance times of submaximal contractions during shoulder abduction and wrist extension were measured. Electromyography (EMG) of muscle activity was recorded bilaterally from the upper trapezius, middle deltoid, and forearm extensor muscles. Root mean square EMG amplitudes were calculated. We found statistically significant associations between peak forces developed during wrist extension and shoulder abduction, and between endurance times of submaximal wrist extension and shoulder abduction. No statistically significant changes in peak force and EMG peak were found over the measurement years. The responses were not statistically significantly influenced by gender, or neck and shoulder pain. However, we observed considerable intra-individual variation in the inter-year measurements particularly for the responses to submaximal contraction. Such large variations represent a challenge when attempting to use the responses to interpret the effects of therapies.

The reproducibility of peak isometric torque and electromyography activity in unfamiliarised subjects using isokinetic dynamometry on repeated days

The aim of this investigation was to examine the intra-subject and group reproducibility of isometric muscle function testing and the associated surface EMG signal repeated over five consecutive days using isokinetic dynamometry. Fifteen physically active volunteers that were unfamiliar with isokinetic dynamometry participated in this study and were asked to attend the laboratory on five consecutive days to complete maximal isometric testing. Surface electromyography was recorded from biceps brachii to examine the electrical activity associated with the peak torque. The intra-subject reproducibility was moderate for isometric torque (mean coefficient of variation (CV) of 6.65%), however the EMG and EMG:torque ratio were somewhat more variable (mean CV of 18.20% and 18.49%, respectively). The group reproducibility showed an intra-class correlation coefficient of r = 0.99, 0.92 and 0.96 for isometric peak torque, EMG and torque: EMG ratio. In addition, the group CV for isometric peak torque, EMG and torque:EMG ratio was 1.03%, 4.10% and 3.38%, respectively. Individuals can show large variations in torque and EMG, however when reproducibility is examined as a group both torque and the associated EMG activity have high reproducibility in physically active subjects, unfamiliarised with isometric dynamometry.

Effects of minimum sampling rate and signal reconstruction on surface electromyographic signals

Signal oversampling is frequently used to prevent distortion in time-series representations. When sampling at rates just above the Nyquist critical frequency ( f c), Shannon’s reconstruction theorem provides an alternative means of circumventing this problem. The purpose of this study was to determine whether surface electromyographic (EMG) data is compromised when sampled just above f c and whether Shannon’s reconstruction theorem can correct these deficiencies, if present. Brief isometric elbow flexion contractions were performed at 100%, 80%, 50%, 25%, 10%, 5% and 2.5% maximum voluntary contraction (MVC) followed by one trial of random cyclic isometric contractions and relaxations. The 2 kHz signal was resampled at 1 kHz and the 2 and 1 kHz signals were reconstructed (2RS and 1RS, respectively) to a sampling rate of 20 kHz. Data were full-wave rectified (FWR) and low-pass filtered (LE). Peak amplitudes of the FWR and LE signals, average EMG (AEMG) amplitudes of the FWR and LE signals, mean power frequency of the raw data, number of gaps, and mean gap time of the LE signals were calculated. Significant differences were present in peak EMG and AEMG measurements between the 1 and 2 kHz, 2RS and 20 kHz signals and occasionally between the 1RS and the 2 kHz, 2RS and 20 kHz signals. These differences, although statistically significant were quite small amounting to less than 0.5% MVC. No significant differences were found for the gaps parameters. The small differences seen, coupled with the processing time required for signal reconstruction, make oversampling as well as signal reconstruction in surface EMG measurements unnecessary.

Manipulations of Leg Mass and Moment of Inertia: Effects on Energy Cost of Walking

To investigate effects that independent alterations in limb mass and moment of inertia about a transverse axis through the hip have on metabolic and mechanical power of walking and peak electromyography (EMG) amplitude. It was hypothesized that increases in metabolic cost would parallel increases in mechanical power, and that EMG amplitude would increase with greater limb mass or limb moment of inertia. Metabolic and mechanical power and lower-extremity EMG were measured on 14 healthy adults walking at 1.5 m.s. Four leg-loading conditions were employed: 1) no load (NL) on the legs; 2) a baseline load (BSLN) condition, with a mean of 2.0 kg per leg distributed on the proximal and distal shank; 3) a load condition with a mean of 2.0 kg per leg distributed on the proximal and distal shank, such that lower-extremity moment of inertia was increased 5% about the hip (MOI5) from the BSLN, but having the same lower-extremity mass as BSLN; and 4) a load condition with a mean of 2.8 kg per leg, concentrated proximally on the shank to increase total lower-extremity mass by 5% (Mass5) from BSLN, but having the same moment of inertia as BSLN. Total subject mass was constant between conditions, as unused leg loads were carried in a waist belt. Changes in mechanical power paralleled changes in metabolic cost as hypothesized. Energy cost increased significantly (4.2%) from NL to BSLN, and from BSLN to MOI5 and Mass5 (3.4 and 4.0%, respectively). EMG did not effectively explain changes in metabolic cost. Independent alterations in limb mass and moment of inertia about the hip joint influence energy cost similarly.

Kinematics of head movement and onset of sternocleidomastoid muscle activity in simulated low-velocity rear-end impacts

Objectives. Rear-end impacts and whiplash injuries are highly associated. More than a million whiplash injuries occur each year in the US.1Malleson A. Chronic whiplash syndrome. Psychosocial epidemic.Canadian Family Physician. 1994; 40: 1906-1909Google Scholar The kinematics of head movement in simulated rear-end impacts has been described. However, the influence of impact awareness remains controversial. In addition, the suggestion that cervical muscles activate too late in rear-end impacts may be incorrect.2Siegmund G.P. Brault J.R. Wheeler J.B. The relationship between clinical and kinematic responses from human subject testing in rear-end automobile collisions.Accident Analysis & Prevention. 2000; 32: 207-217Google Scholar The goal of this study was to analyze the kinematics of head movement in rear-end impacts related to 2 impact magnitudes, impact awareness and onset of sternocleidomastoid (SCM) muscle response. Study design. The Human Research Ethics Board at the University of Alberta approved this study. Thirty subjects completed the study. Each subject underwent 3 impacts: 1 slow unexpected (4.5 m/sec/sec), 1 fast unexpected (10.0 m/sec/sec), and 1 fast expected impact of the same magnitude as the fast unexpected impact. Kinematics of head movement was simultaneously recorded with a custom accelerometer board and the use of video cameras. Angular head displacement, and angular and linear head acceleration were recorded. Normalized SCM surface electromyography (EMG) was obtained. Onset and peak time for the EMG and the kinematics were determined. Onset time was defined as the time in which 5% of the magnitude value of the peak occurred. Peak time was defined as the time in which the maximum value of the variable was reached. Repeated-measures statistical method was used to analyze the head movement behavior associated with impact velocity and expectation. The same statistical method was used to determine whether muscle activity or head movement was initiated first. Results. The video camera and accelerometer data presented a good agreement. Subjects presented an initial rearward movement in which the head moved backward followed by a forward movement of the head. The rearward angular head displacement almost doubled (∼13 degrees) with increased impact magnitude (P < .05). The peak magnitude of rearward and forward angular acceleration increased 2 to 3 times with increased impact magnitude (P < .05). Rearward and forward linear displacement was 2.5-3.5 times higher for the fast than the slow unexpected impacts (P < .05). There were no significant differences in the magnitude of angular head acceleration, angular head displacement, and linear head acceleration regarding awareness (P>0.05). The onset time of SCM peak EMG ranged from 78-114 ms later than peak of linear head acceleration for all groups (P < .05). The onset of the SCM peak EMG ranged from 136-188 ms earlier than the peak rearward angular head displacement in all impacts (P < .05). Onset time of peak SCM EMG was significantly earlier (30 ms) than the peak angular head acceleration for the fast unexpected impact (P < .05). Conclusions. Kinematics of head movement increased with increased impact magnitude. Magnitude of angular head displacement was within physiologic limits and do not support the hyperextension theory. Temporal and amplitude awareness did not produce different magnitude in kinematics of head movement. The temporal relationship between the SCM and angular head acceleration is different from the temporal relationship between the SCM and linear head acceleration.

強度を自己選択した運動中における骨格筋活動と強度認知との関係

When individuals select their own exercise intensity, the factors contributing to the perception of exercise intensity are important. In particular, it is not clear whether the activity of the skeletal muscles influences the self-selected (SS) intensity. Previous investigations have reported that effort sense increases in response to greater neuromotor activity as measured by electromyography (EMG) during dynamic exercise. The purpose of this study was to examine the effects of skeletal muscle activity on SS exercise intensity by investigating the relationship between the ratings of perceived exertion (RPE) and EMG response. Seven healthy men (mean±SD, 22.2±0.4 years) performed two 20-min sessions of cycling exercise with a protocol involving the SS method, which consisted of 5 min of fixed-load cycling at 70% of maximal oxygen uptake followed by 15 min of cycling with the SS method (SSFL_<70%>). RPE in the femoral region (RPE-peripheral: RPEp) was not correlated with the percentage peak wattage (% W_<peak>) and EMG indices in the femoral region during the SS protocol. While correlation coefficients between RPEp and EMG indices showed significantly negative values during the SSFL_<70%> protocol, there was no significant correlation between them during the SS protocol. These results during SSFL_<70%> suggested that the decrease of agonist muscle exertion and stress in the joint were caused by the increase in revolutions per minute during cycling. The increase in revolutions per minute during SSFL_<70%> appears to affect the decrease in the exertion of the agonist muscles and the stress in the joint and subsequent decline in RPEp. Since exercise intensity with the SS method is thought to be selected on the basis of cognitive feedback, these results suggest that tension of the skeletal muscle and agonist muscular exertion do not influence the perception of intensity during exercise with the SS method.