Relative Muscle Activity Research Articles

Reliability and minimal detectable change in scapulothoracic neuromuscular activity

Alterations in scapular muscle activity, including excess activation of the upper trapezius (UT) and onset latencies of the lower trapezius (LT) and serratus anterior (SA) muscles, are associated with abnormal scapular motion and shoulder impingement. Limited information exists on the reliability of neuromuscular activity to demonstrate the efficacy of interventions. The purpose of this study was to characterize the reproducibility of scapular muscle activity (mean activity, relative onset timing) over time and establish the minimal detectable change (MDC). Surface electromyography (sEMG) of the UT, LT, SA and anterior deltoid (AD) muscles in 16 adults were captured during an overhead lifting task in two sessions, one-week apart. sEMG data were also normalized to maximum isometric contraction and the relative onset and mean muscle activity during concentric and eccentric phases of the scapular muscles were calculated. Additionally, reliability of the absolute sEMG data during the lifting task and MVIC was evaluated. Both intrasession and intersession reliability of normalized and absolute mean scapular muscle activity, assessed with intraclass correlation coefficients (ICC), ranged from 0.62 to 0.99; MDC values were between 1.3% and 11.7% MVIC and 24 to 135mV absolute sEMG. Reliability of sEMG during MVIC was ICC=0.82–0.99, with the exception of intersession upper trapezius reliability (ICC=0.36). Within session reliability of muscle onset times was ICC=0.88–0.97, but between session reliability was lower with ICC=0.43–0.73; MDC were between 39 and 237ms. Small changes in scapular neuromuscular mean activity (>11.7% MVIC) can be interpreted as meaningful change, while change in muscle onset timing in light of specific processing parameters used in this study is more variable.

Effect of Gait Speed on Muscle Activity Patterns and Magnitude During Stance

This study aims to assess the influence of gait speed (manipulated through cadence) on muscle activity patterns and activation degree during stance. Thirty-five healthy individuals participated in this study. Surface electromyographic activity from the gastrocnemius medialis (GM), gluteus maximus (GMax), biceps femoris (BF) and rectus femoris (RF) was acquired with subjects walking at three different speeds. Speed influenced: (1) relative motor activity patterns at heel strike, midstance-propulsion transition and propulsion; (2) the activity level of RF, GMax, GM and BF, in decreasing order, with higher activity at the fastest and slowest speeds. In general, muscle activity was higher at the fastest and slowest speeds than at the self-selected speed and only the activity of the main actions in each subphase remained stable. These findings suggest that gait speeds different from the self-selected speed influence not only activity levels but also relative muscle activity patterns. As a result, caution is advised when choosing standard speeds in gait studies, as this can lead to increased variability in relative muscle activity patterns.

Changes in recruitment of pelvic stabilizer muscles in people with and without sacroiliac joint pain during the active straight-leg-raise test

Though the active straight leg raise (ASLR) test has been proposed as a reliable methodology for assessment of load transfer through the pelvis in patients with sacroiliac joint pain (SIJP), the tonicity and timing of muscle activation during the ASLR test have not been investigated. In clinical experiments, besides the ASLR test score, an increased duration of the test is also used for diagnosis of SIJP. This study was a cross-sectional design of electro-myographic pattern of sacroiliac stabilizer muscles to establish a platform for comparison of patients with SIJP and healthy controls. To identify if the subjects with SIJP show changes in electromyographic pattern of sacroiliac stabilizer muscles as well as any duration difference in such tests for both groups. Fifteen female patients with sacroiliac pain and the same number of healthy females at the same age were participated in this study. All the patients were diagnosed as positive ASLR as well as self reported maximum pain over the sacroiliac joint. Surface electromyographic activity was recorded from rectus abdominus, external oblique, internal oblique, adductor longus, biceps femoris, gluteus maximus and erector spinea during ASLR. Tonicity and onset of muscle activity in relation to the initiation of the ASLR and their duration were also compared. The participants with SIJP exhibited a significantly increased latency at the onset of adductor longus following the initiation of the ASLR test (P=0.002) as compared to the healthy controls. A significant difference was also observed in tonicities of external oblique, biceps femoris, gluteus maximus and erector spinea as well as the duration of leg rising (P < 0.05) between the two groups. These findings suggest that an alteration in the motor control strategy for lumbopelvic stabilization in patients with SIJP may influence load transfer through the pelvic.

Effect of rollover footwear on metabolic cost of ambulation, lower limb kinematics, kinetics, and EMG related muscle activity during walking

BackgroundFootwear with a curved sole profile shifts the point of contact between the shoe and floor anteriorly compared to a flat shoe. There have been various reports of changes in ground reaction forces, external joint moments, and (rather inconclusively) muscle activity and energy consumption during walking in this “rollover” footwear [1-6]. The aim of this study was to investigate the effect of two types of rollover footwear (one a new prototype) on walking speed, metabolic cost of gait, lower limb kinematics, kinetics and EMG muscle activity.MethodsTwenty subjects walked in four footwear conditions: (1) a flat control shoe; (2) a flat control shoe weighted to match the mass of the new rollover shoe prototype; (3) the new prototype rollover shoe; (4) a MBT shoe. Data relating to metabolic energy and temporal aspects of gait were collected during a 6 minute walk test. Data on the lower limb kinematics, joint moments, muscle activity and foot pressure were collected during walking on a straight 10 metre course.ResultsThe curved sole moved the contact point under the shoe anteriorly during early stance. This altered ankle moments and reduced ankle plantarflexion after initial contact. In mid stance the roll over footwear reduced ankle dorsiflexion and overall the ankle moved less in roll over footwear. Ground reaction force loading rates were increased by the rollover footwear. There were notable elevations in early stance calf EMG activity. Effects on energy cost of ambulation were negligible. Rollover footwear reduced plantar pressures under the heel and forefoot, and redistributed pressure towards the midfoot. Shoe weight had no effect on any parameters.ConclusionRollover footwear is able to modify ankle kinematics and moments and the activity of some ankle musculature. Effects proximal to the leg were small. There were no effects on the temporal or energy aspects of gait.

Hot ambient conditions do not alter intermittent cycling sprint performance

ObjectivesTo investigate the effect of hot exposure on the ability to perform intermittent cycling sprints. DesignRepeated measures. MethodsTen male volunteers performed 35min of intermittent cycling comprising of 8 maximal 6-s sprints interspersed by 1min of passive recovery followed by 4min of constant-load pedaling (1Wkg−1 of body weight) on a cycle ergometer in control (24̊C, 24%rH) and hot (40̊C, 40%rH) environments. ResultsPeak power output did not decrease during the exercise and was not dependent on the environmental temperature (average of 767±120W in control and 767±119W in hot, NS). Skin temperatures (e.g., chest: 36.8±0.8 vs. 32.7±0.6°C), heart rate (132±13 vs. 118±13bpm) and rating of perceived exertion (13±3 vs. 11±3) were higher (all p<.05) in hot than control environment. However, EMG activity (RMS, vastus lateralis) and neuromuscular efficiency (power/RMS ratio) were similar at the two environmental conditions. ConclusionsDespite higher cardiovascular and perceptual strain in the hot trial, heat exposure did not alter neither peak power output nor related muscle activation and neuromuscular efficiency in the absence of hyperthermia (average core temperature of 37.6±0.3°C in control vs. 37.7±0.4°C in hot, NS).

Efficacy of current and novel electromyographic normalization methods for lower limb high-speed muscle actions

The aim of this study was to assess the efficacy of electromyography (EMG) normalization methods for a high-speed 20-m sprint. Comparisons were based on intra-individual reliability and magnitude of normalized EMG signals from three repeat sessions separated by 1 day (between days) and 1 week (between weeks) from the initial test. Surface EMGs were recorded (n=16) from the medial and lateral gastrocnemius and soleus during the normalization methods (isometric: maximum/sub-maximum/body weight; isotonic: maximum/sub-maximum/body weight; isokinetic: 1.05 rad · s–1, 1.31 rad · s–1, 1.83 rad · s–1; squat jump). The EMG data from the 20-m sprint were normalized using each method and using the within-sprint peak EMG (sprint peak). Intra-individual reliability of the EMG was assessed using typical error of measurement as a percentage of intra-individual coefficient of variance (TEMCV%). Sprint peak normalization improved intra-individual reliability of EMG (soleus: <4.91CV%; medial gastrocnemius: <6.2CV%; lateral gastrocnemius: <7.1CV%) compared with un-normalized EMG (soleus: <13.3CV%; medial gastrocnemius: <16.5CV%; lateral gastrocnemius: <16.3CV%) both between days and between weeks. Squat jump normalization improved the soleus (<11.2CV%) and medial gastrocnemius (<15.7CV%) reliability between days and weeks and provided a representative measure of triceps surae muscle activation. The intra-individual reliability of the medial gastrocnemius EMG data was improved both between days and weeks when using isotonic normalization. Isometric and isokinetic normalization showed no improvement in intra-individual reliability either between days or weeks for any muscle. The method of normalization influenced the between-stride muscle interaction during the 20-m sprint. The results of this study suggest that peak normalization can be used to normalize high-speed muscle actions, while normalizing EMG to a squat jump may provide an alternative method to represent relative muscle activation.

Neural control of leg stiffness during hopping in boys and men

The purpose of the study was to investigate whether boys and men utilise different control strategies whilst hopping. Eleven boys (11–12 yr old) and ten men completed hopping at 1.5 Hz, 3.0 Hz and at their preferred frequency. A footswitch measured contact and flight times, from which leg stiffness was calculated. Simultaneously, surface electromyograms (EMGs) of selected lower limb muscles were recorded and quantified for each 30 ms period during the first 120 ms post-ground contact. At 1.5 Hz there were no differences between the groups in relative stiffness or muscle activity. At 3.0 Hz men had significantly shorter contact times ( P = 0.013), longer flight times ( P = 0.002), greater relative stiffness ( P = 0.01) and significantly greater soleus ( P = 0.012) and vastus lateralis ( P < 0.001) activity during the initial 30 ms post-ground contact. At the preferred frequency men hopped significantly faster than the boys ( P = 0.007), with greater leg stiffness ( P < 0.01) and with more extensor activity in most time periods. Boys and men demonstrated similar control strategies when hopping at a slow frequency, but when hopping frequency increased men were able to better increase feedforward and reflex muscle activity to hop with greater relative stiffness.

Influence of bite force on jaw muscle activity ratios in subject-controlled unilateral isometric biting

Ratios of muscle activities in unilateral isometric biting are assumed to provide information on strategies of muscle activation independently from bite force. If valid, this assumption would facilitate experiments as it would justify subject-control instead of transducer-based force control in biting studies. As force independence of ratios is controversial, we tested whether activity ratios are associated with bite force and whether this could affect findings based on subject-controlled force. In 52 subjects, bite force and bilateral masseter and temporalis electromyograms were recorded during unilateral biting on a transducer with varying force levels and with uniform subject-controlled force. Working/balancing and temporalis/masseter ratios of activity peaks were related to bite force peaks. Activity ratios were significantly but weakly correlated with the bite force. The subject-controlled force varied within ±25% around the prescribed force in 95% of all bites. This scatter could cause a variation of group mean activity ratios of at most ±6% because of the weak correlation between bite force and ratios. As this small variation is negligible in most cases, subject-control of bite force can be considered an appropriate method to obtain group means of relative muscle activation in particular when force control with transducers is not feasible.

Soleus stretch reflex in subjects with cerebrovascular accident

Aims The conclusion that circumferential pressure decreases reflex activity in subjects with neuromuscular disorders including cerebrovascular accidents has recently come under scrutiny due to the methods used to analyze its effects. Thus far, studies used to determine circumferential pressure's efficacy on motor neuron reflex excitability have mainly used the H-reflex technique on resting muscle. The purpose of this study was to investigate the effect that circumferential pressure has on the soleus stretch reflex (SSR) when superimposed onto a voluntary ramp movement in patients with cerebrovascular accident (CVA). Methods Thirteen patients with CVA volunteered for this study. SSR's were investigated before, during and after the application of pressure to the calf. Twenty-five SSR's were recorded and averaged for each experimental phase. Peak to peak amplitudes were measured and then normalized for comparisons. Reflex latencies were also measured. Friedman Repeated Measures Analysis of Variance on Ranks were used to analyze the differences in SSR latency and amplitude from baseline values. Findings Patients with CVA showed a decrease of 35% (P&lt;0.006) in SSR mean amplitude. Postpressure values and latencies were not significantly different from baseline values. Conclusions The results show circumferential pressure has an inhibitory effect on spinal cord muscular reflexes for patients with CVA and may be used as a supplement to other treatments in temporarily reducing spinal cord reflex related muscle activity associated with a neurological dysfunction

Indications for jaw gape‐related control of relative muscle activation in sequent chewing strokes

Jaw muscle activity ratios in unilateral isometric biting differ from ratios of unilateral chewing but approach the latter if the jaw gape in biting is made as small as the minimum interocclusal distance (MID) of chewing. Especially, the masseter working/balancing side ratio (W/B-ratio) becomes as asymmetric as in chewing, because of reduction in balancing side (BS) masseter activity. This behaviour of ratios might reflect a 'chewing-specific' motor strategy induced when isometric biting is performed with a 'chewing-like' gape. If this hypothesis applies, activity ratios should be associated with MIDs of sequent chewing strokes in a similar manner as with incremented jaw gapes in isometric biting. To test this prediction, bilateral surface electromyograms of masseter and anterior temporalis muscles and incisor movements were recorded during unilateral chewing in 52 subjects. W/B-ratios of masseter and temporalis activities and temporalis/masseter-ratios on both sides were calculated. The ratios were related to MIDs of consecutive chewing cycles. Three of the four ratios were associated with masticatory MID in the same manner as with jaw gape in isometric biting. In particular with decreasing MID, the masseter W/B-ratio increased from 1.5 to 2.2 (P < 0.01). This increase in asymmetry was attributed to a stronger decrease in masseter activity on the BS than on the working side. We conclude that relative jaw muscle activation is associated with interocclusal distance in a similar way in isometric biting and in chewing. This analogy supports the idea of a common jaw gape-related neuromuscular strategy facilitated by afferent signalling of interocclusal distance.

Exercise Focused on Multiarticular Movement to Improve Muscle Activity During Gait and Single-leg Standing for Participants with Hip Osteoarthritis by Using Electromyogram and Three-dimensional Motion Analysis

[Purpose] We investigated how two types of exercise affect walking and single-leg standing in people with hip osteoarthritis (OA) using surface electromyogram (EMG) and three-dimensional (3D) motion analysis system. [Subjects and Methods] Participants were 18 female diagnosed as having hip OA. We defined hip abduction movement with a tube band wrapped around the thigh as monoarticular- (Mono-) group and the group using resisted joint extension with rotation movement as multiarticular- (Multi-) group. EMG measured the activity of the gluteus maximus (GMax) and gluteus medius (GMed) of affected side during 10 meters gait and single-leg standing on affected side. 3D motion analysis calculated the total locus length (TL) of anterior superior iliac spine (ASIS) of affected side during single-leg standing. These results were analyzed by t-test. [Results] After each exercise, %IEMG of GMax in Mono-group showed a significant decrease during the stance phase. In Multi group, GMax and GMed were significantly increased during the stance phase, whereas GMax was significantly decreased during the swing phase. TL during single-leg standing in Multi group decreased significantly. [Conclusion] These results indicate that exercise focusing on multiarticular movement improves muscle activity and stability in relation to daily activities.

Medial And Lateral Gastrocnemius Activation Differences During Heel Raise Exercise With Three Different Foot Positions

Instructional guidelines from some national exercise certification organizations recommend performing heel raise exercise with varying initial foot positions to alter the involvement of the gastrocnemius' medial (MG) or lateral (LG) head. PURPOSE: To compare MG and LG activation during the concentric (CP) and eccentric (EP) phases of heel raise exercise using neutral (N), internally-rotated (IR) and externally-rotated (ER) foot positions. The term "foot position" was maintained for consistency with instructional texts, though the initial foot position reflects hip rotation. METHODS: Twelve healthy subjects (9 male, 3 female; 24.0 ± 3.8yrs) with resistance training experience performed free-weight (bar loaded to 30% body mass) heel raise exercise on a 3.8 cm block. Surface electromyographic (EMG) activity was recorded during five repetitions under each of the N, IR and ER foot positions, divided into CP and EP phases, and ensemble averaged within phase. Mean EMG amplitude, normalized to maximum voluntary contraction, was calculated. Separate two-factor (position by head) repeated measures analysis of variance were used for each phase. Simple main effects post hoc analyses of the significant (P <.05) interactions were conducted. RESULTS: During EP, significantly greater MG activity compared to LG activity was revealed for both N and ER. During CP, significantly greater LG activity compared to the MG occurred for IR. Further, post hoc analyses on the EP revealed that MG activity using ER was significantly greater than MG activity using IR or N. Likewise, analysis of CP revealed that LG activity using IR was significantly greater than LG activity using ER or N. CONCLUSION: Altering foot positions during the heel raise exercise does alter relative muscle activation as measured by surface EMG. The MG is activated to a significantly greater extent than the LG during EP using N and ER, while the LG displays significantly greater muscle activity than the MG during CP using IR. Further research is recommended to elucidate the role of the contraction phases in these differences.

Application of Autocorrelation and Cross-correlation Analyses in Human Movement and Rehabilitation Research

Technical note. To provide background theory and information and to describe relevant applications of autocorrelation and cross-correlation methodology as they apply to the field of motor control in human movement and rehabilitation research. Commonly used methodologies for pattern and event recognition, determination of muscle activation timing for investigation of movement coordination, and motor control are generally difficult to implement, particularly with large datasets. A brief description of the underlying mathematical theory of correlation analyses is given, followed by 4 different examples of how this methodology is useful for research in the movement sciences. Examples demonstrating the utility of correlation analyses are presented from several different studies conducted at the University of Waterloo. Autocorrelation was used to demonstrate the presence of 60-Hz noise in an electromyography signal that was not visible in the raw data. A "top-down" paraspinal muscle activation pattern was demonstrated for healthy adults during gait, with the use of cross-correlation. Cross-correlation was also used to quantify coactivation of bilateral gluteus medius muscles during standing in individuals who developed low-back pain. Gender differences in gluteus medius control of mediolateral center of pressure were seen with the use of cross-correlation. Autocorrelation and crosscorrelation have been shown to be an effective tool for several different applications in the movement sciences. Examples of the method's utility include noise detection within a signal, determination of relative muscle activation onsets for postural control, objective quantification of muscle coactivation, and relating muscle activations with mechanical events.

Motor control of jaw muscles in chewing and in isometric biting with graded narrowing of jaw gape

When a certain bite force is applied during unilateral chewing, the combination of jaw elevator muscle activities is different than when a comparable force is applied in unilateral isometric biting, e.g. on a force transducer. Masticatory peak force is generated in a nearly isometric phase of the chewing cycle, with a jaw gape of about 1 mm. In contrast, peak force in isometric biting on force measuring equipment usually induces jaw gapes of 6 mm or even more. Therefore, we tested the hypothesis that the jaw gape influences relative activation of elevator muscles in unilateral isometric biting. We further examined whether such influence could explain the different activity combinations of chewing and isometric biting. In thirty asymptomatic males, masseter and temporalis activities were recorded during intermittent isometric biting with jaw gapes of 6, 5, 3, 2 and 1 mm and during unilateral chewing. Activity combinations were described by working/balancing ratios and by temporalis/masseter ratios. With decreasing jaw gape the working/balancing ratio of the posterior temporalis decreased (P < 0.002) while that of the masseter increased (P < 0.001). Likewise, the temporalis/masseter ratio on the balancing side increased (P < 0.001). With decreasing jaw gape, activity ratios of isometric biting approached ratios of chewing. We conclude that: (i) relative jaw muscle activation in isometric biting depends on the jaw gape, (ii) relative muscle activation in chewing resembles relative activation of isometric biting with a small 'chewing-like' gape. This suggests that characteristic activity combinations in chewing are mainly a result of the approximately isometric contraction during the slow closing phase of the chewing cycle.

Elevated PEM (phasic electromyographic metric) rates identify rapid eye movement behavior disorder patients on nights without behavioral abnormalities.

To determine the validity of the phasic electromyographic metric (PEM) to differentiate patients with a history suggestive of rapid eye movement behavior disorder (REMBD) on laboratory nights without overt dream-enactment behavior. PEM was quantified as the % of 2.5-sec intervals with phasic muscle activity of 100-msec duration with an amplitude of at least 4 times background activity in 11 patients and 31 elderly controls. Data were derived from both REM and NREM sleep from 5 muscle groups (mentalis, left/right anterior tibialis, left/right brachioradialis). Relative to controls, REMBD patients had significantly higher levels of PEM activity in all recordings. The largest differences occurred during REM sleep for the mentalis and brachioradialis channels. Similar results were obtained by limiting quantification of PEM to the final REM period of the night and could be accomplished by individuals with no previous familiarity with polysomnography. PEM may be a useful metric to characterize the REM related phasic muscle activity on patients with a history of REMBD, even when no overt dream-enactment behaviors are detected on a laboratory night.

Trunk biomechanics during maximum isometric axial torque exertions in upright standing

Background Activities involving axial trunk rotations/moments are common and are considered as risk factors for low back disorders. Previous biomechanical models have failed to accurately estimate the trunk maximal axial torque exertion. Moreover, the trunk stability under maximal torque exertions has not been investigated. Methods A nonlinear thoracolumbar finite element model along with the Kinematics-driven approach is used to study biomechanics of maximal axial torque generation during upright standing posture. Detailed anatomy of trunk muscles with six distinct fascicles for each abdominal oblique muscle on each side is considered. While simulating an in vivo study of maximal axial torque exertion, effects of antagonistic coactivities, coupled moments and maximum muscle stress on results are investigated. Findings Predictions for trunk axial torque strength and relative muscle activities compared well with reported measurements. Trunk strength in axial torque was only slightly influenced by variations in coupled moments. Presence of abdominal antagonistic coactivities and alterations in maximum strength of muscles had, however, greater effect on maximal torque exertion. Abdominal oblique muscles play crucial role in generating moments in all three planes while back muscles are mainly effective in balancing moments in sagittal/coronal planes. Trunk stability is not of a concern in maximum axial torque exertions nor is it improved by antagonistic abdominal coactivities. Interpretation In contrast to previous biomechanical model studies, the Kinematics-driven approach accurately predicts the trunk response in maximal isometric axial torque exertions by taking into account detailed anatomy of abdominal oblique muscles while satisfying equilibrium requirements in all planes/directions. In maximal torque exertions, the spine is at much higher risk of tissue injury due to large segmental loads than of instability.

Trunk Muscle Activity During Stability Ball and Free Weight Exercises

The purpose of this investigation was to compare trunk muscle activity during stability ball and free weight exercises. Nine resistance-trained men participated in one testing session in which squats (SQ) and deadlifts (DL) were completed with loads of approximately 50, 70, 90, and 100% of one-repetition maximum (1RM). Isometric contractions during 3 stability ball exercises (quadruped (QP), pelvic thrust (PT), ball back extension (BE)) were also completed. During all exercises, average integrated electromyography (IEMG) from the rectus abdominus (RA), external oblique (EO), longissimus (L1) and multifidus (L5) was collected and analyzed. Results demonstrate that when expressed relative to 100% DL 1RM, muscle activity was 19.5 +/- 14.8% for L1 and 30.2 +/- 19.3% for L5 during QP, 31.4 +/- 13.4% for L1 and 37.6 +/- 12.4% for L5 during PT, and 44.2 +/- 22.8% for L1 and 45.5 +/- 21.6% for L5 during BE. IEMG of L1 during SQ and DL at 90 and 100% 1RM, and relative muscle activity of L5 during SQ and DL at 100% 1RM was significantly greater (P < or = 0.05) than in the stability ball exercises. Furthermore, relative muscle activity of L1 during DL at 50 and 70% 1RM was significantly greater than in QP and PT. No significant differences were observed in RA and EO during any of the exercises. In conclusion, activity of the trunk muscles during SQs and DLs is greater or equal to that which is produced during the stability ball exercises. It appears that stability ball exercises may not provide a sufficient stimulus for increasing muscular strength or hypertrophy; consequently, the role of stability ball exercises in strength and conditioning programs is questioned. SQs and DLs are recommended for increasing strength and hypertrophy of the back extensors.

Complex airway behavior and paradoxical responses to bronchoprovocation

Heterogeneity of airway constriction and regional ventilation in asthma are commonly studied under the paradigm that each airway's response is independent from other airways. However, some paradoxical effects and contradictions in recent experimental and theoretical findings suggest that considering interactions among serial and parallel airways may be necessary. To examine airway behavior in a bronchial tree with 12 generations, we used an integrative model of bronchoconstriction, including for each airway the effects of pressure, tethering forces, and smooth muscle forces modulated by tidal stretching during breathing. We introduced a relative smooth muscle activation factor (T(r)) to simulate increasing and decreasing levels of activation. At low levels of T(r), the model exhibited uniform ventilation and homogeneous airway narrowing. But as T(r) reached a critical level, the airway behavior suddenly changed to a dual response with a combination of constriction and dilation. Ventilation decreased dramatically in a group of terminal units but increased in the rest. A local increase of T(r) in a single central airway resulted in full closure, while no central airway closed under global elevation of T(r). Lung volume affected the response to both local and global stimulation. Compared with imaging data for local and global stimuli, as well as for the time course of airway lumen caliber during bronchoconstriction recovery, the model predictions were similar. The results illustrate the relevance of dynamic interactions among serial and parallel pathways in airway interdependence, which may be critical for the understanding of pathological conditions in asthma.

Acute Effects of Whole Body Vibration on Vertical Jump Performance and Related Muscle Activity

Acute Effects of Whole Body Vibration on Vertical Jump Performance and Related Muscle Activity

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.