Effect of instructions on EMG during the bench press in trained and untrained males

Strength and rehabilitation professionals strive to emphasize certain muscles used during an exercise and it may be possible to alter muscle recruitment strategies with varying instructions. This study aimed to determine whether resistance trained and untrained males could selectively activate the pectoralis major or triceps brachii during the bench press according to various instructions. This study included 13 trained males (21.5 ± 2.9 years old, 178.7 ± 7.0 cm, 85.7 ± 10.7 kg) and 12 untrained males (20.3 ± 1.6 years old, 178.8 ± 9.4 cm, 74.6 ± 17.3 kg). Participants performed a bench press one-repetition maximum (1-RM) test, 3 uninstructed repetitions at 80% 1-RM and two more sets of three repetitions with instructions to isolate the chest or arm muscles. Electromyography (EMG) was obtained from the pectoralis major, anterior deltoid, and the long head and short head of the triceps brachii. Maximum EMG activity normalized to 1-RM for each muscle was averaged over the three repetitions for each set and compared between the uninstructed, chest-instructed and arm-instructed conditions among the groups. The trained participants had a greater 1-RM (126.2 ± 30.6 kg) than the untrained participants (61.6 ± 14.8 kg) (P < 0.01). EMG activity was not different between the groups for any of the instructions (P > 0.05). When the group data was combined, short head of the triceps activity was significantly lower in the chest instruction (80.1 ± 19.3%) when compared to the uninstructed (85.6 ± 23.3%; P = 0.01) and arm-instructed (86.0 ± 23.2; P = 0.01) conditions. It can be concluded that instructions can affect muscle activation during the bench press, and this is not dependent on training status.     

Lower limb mechanical asymmetry during repeated treadmill sprints

Stride mechanical imbalances between the lower limbs may be detrimental to performance and/or increase injury risks. This study describes the time course and magnitude of asymmetries in running mechanical variables during repeated treadmill sprints and examines whether inter-limb differences in sprinting mechanics increase with fatigue. Thirteen non-injured male athletes performed five 5-s sprints with 25-s recovery on an instrumented treadmill, allowing the continuous (step-by-step) measurement of running kinetics/kinematics and spring-mass characteristics calculation. For each variable, bilateral leg asymmetry (BLA%) between the left and the right leg was defined as: {[(high value − low value)/low value] × 100}. BLA% for propulsive power and horizontal forces averaged ∼12–13%, while lower values occurred for step-averaged values of running velocity, resultant and vertical forces (all ∼4%). For all sprints, kinematic BLA% ranged from 1.6 ± 1.0% (swing time) to 9.0 ± 5.3% (aerial time). BLA% for vertical and leg stiffness was 6.4 ± 4.9% and 7.6 ± 3.6%, respectively. While distance covered decreased across repetitions (P < 0.05), there was no significant interaction between sprint repetitions and leg side for any of the mechanical variables studied (all P > 0.05). Although inter-limb differences were observed for many running kinetics/kinematics and spring-mass characteristics during repeated treadmill sprints, the lack of interaction between sprint repetitions and leg side suggests that lower limbs fatigued at a similar rate.     

H-reflex excitability is inhibited in soleus,but not gastrocnemius,at the short-latency response of a horizontal jump-landing task

Impaired spinal-level neuromuscular control is suggested to contribute to instability and injury during dynamic landing tasks. Despite this suggestion, spinal-level neuromuscular control is yet to be examined during a horizontal jump-landing task. The aim of the current study was to assess changes in H-reflexes and its reliability at the short-latency response of landings from short and long distances. Eight healthy individuals (five male, three female; age, 22 ± 1.2 yrs; height, 178 ± 8.1 cm; weight, 72 ± 15.7 kg) participated in the study. H-reflexes were evoked at the SLR in the soleus and medial gastrocnemius muscles, during two landing conditions: 25% and 50% of maximal broad jump distance. H-reflexes were expressed relative to the background electromyography (EMG) and maximal M-wave responses (M-max). Soleus H-reflexes were inhibited when landing from shorter distance (25%, 13.9 ± 7.6%; 50%, 8.3 ± 6.5%; p < 0.01). No change in H-reflex excitability was observed in medial gastrocnemius. Background EMG was unaltered across landing conditions. Inhibition of soleus H-reflex excitability from 25% to 50% landing condition indicates a reduced contribution of Ia-afferent feedback to the alpha-motor neuron during landings from greater distances, which may contribute to stiffness regulation at the ankle joint. Unaltered H-reflex excitability of medial gastrocnemius is most likely attributed to its functional role during the landing task.     

Treadmill based reference running data for healthy subjects is dependent on speed and morphological parameters

ObjectiveTo obtain spatiotemporal and dynamic running parameters of healthy participants and to identify relationships between running parameters, speed, and physical characteristics.MethodA dynamometric treadmill was used to collect running data among 417 asymptomatic subjects during speeds ranging from 10 to 24 km/h. Spatiotemporal and dynamic running parameters were calculated and measured.ResultsResults of the analyses showed that assessing running parameters is dependent on running speed. Body height correlated with stride length (r = 0.5), cadence (r = −0.5) and plantar forefoot force (r = 0.6). Body mass also had a strong relationship to plantar forefoot forces at 14 and 24 km/h and plantar midfoot forces at 14 and 24 km/h.ConclusionThis reference data base can be used in the kinematic and kinetic evaluation of running under a wide range of speeds.     

Modulation of motor variability related to experimental muscle pain during elbow-flexion contractions

Experimental muscle pain typically reorganizes the motor control. The pain effects may decrease when the three-dimensional force components are voluntarily adjusted, but it is not known if this could have negative consequences on other structures of the motor system. The present study assessed the effects of acute pain on the force variability during sustained elbow flexion when controlling task-related (one-dimensional) and all (three-dimensional) contraction force components via visual feedback. Experimental muscle pain was induced by bolus injection of hypertonic saline into m. biceps brachii, and isotonic saline was used as control. Twelve subjects performed sustained elbow flexion at different levels of the maximal voluntary contraction (5–30% MVC) before, during, and after the injections. Three-dimensional force components were measured simultaneously with surface electromyography (EMG) from elbow flexors and auxiliary muscles. Results showed that force variability was increased during pain compared to baseline for contractions using one-dimensional feedback (P < .05), but no significant differences were found for three-dimensional feedback. During painful contractions (1) EMG activity from m. trapezius was increased during contractions using both one-dimensional and three-dimensional feedback (P < .05), and (2) the complexity of EMG from m. triceps brachii and m. deltoid was higher for the three-dimensional feedback (P < .05). In conclusion, the three-dimensional feedback reduced the pain-related functional distortion at the cost of a more complex control of synergistic muscles.     

Partial body weight support treadmill training speed influences paretic and non-paretic leg muscle activation,stride characteristics,and ratings of perceived exertion during acute stroke rehabilitation

BackgroundIntensive task-specific training is promoted as one approach for facilitating neural plastic brain changes and associated motor behavior gains following neurologic injury. Partial body weight support treadmill training (PBWSTT), is one task-specific approach frequently used to improve walking during the acute period of stroke recovery (<1 month post infarct). However, only limited data have been published regarding the relationship between training parameters and physiologic demands during this early recovery phase.ObjectiveTo examine the impact of four walking speeds on stride characteristics, lower extremity muscle demands (both paretic and non-paretic), Borg ratings of perceived exertion (RPE), and blood pressure.DesignA prospective, repeated measures design was used.MethodsTen inpatients post unilateral stroke participated. Following three familiarization sessions, participants engaged in PBWSTT at four predetermined speeds (0.5, 1.0, 1.5 and 2.0 mph) while bilateral electromyographic and stride characteristic data were recorded. RPE was evaluated immediately following each trial.ResultsStride length, cadence, and paretic single limb support increased with faster walking speeds (p ⩽ 0.001), while non-paretic single limb support remained nearly constant. Faster walking resulted in greater peak and mean muscle activation in the paretic medial hamstrings, vastus lateralis and medial gastrocnemius, and non-paretic medial gastrocnemius (p ⩽ 0.001). RPE also was greatest at the fastest compared to two slowest speeds (p < 0.05).ConclusionsDuring the acute phase of stroke recovery, PBWSTT at the fastest speed (2.0 mph) promoted practice of a more optimal gait pattern with greater intensity of effort as evidenced by the longer stride length, increased between-limb symmetry, greater muscle activation, and higher RPE compared to training at the slowest speeds.     

The effects of foot cooling on postural muscle responses to an unexpected loss of balance

The purpose of this study was to examine the role of foot sole somatosensory information during reactive postural control. Twenty young adults (22.0 ± 1.4 y) participated in this study. Baseline skin sensitivity from the foot sole was assessed using Semmes-Weinstein monofilaments. Postural muscle responses, in the form of electromyographic (EMG) onset latencies and amplitudes, were then obtained while participants recovered their balance while standing on a moveable platform that could translate in either the forward or backward direction. Following these baseline measures, the participant’s foot soles were immersed in a 0–2 °C ice-water bath for 12 min followed by a 3 min re-immersion period. At the completion of foot cooling, foot sole sensitivity and postural muscle responses to the balance perturbations were re-assessed. Results indicated that the foot cooling protocol reduced foot sole sensitivity and remained reduced throughout the duration of the experiment (p < 0.001). The reduction in foot sole somatosensation resulted in the soleus EMG onset latency being delayed by 3 ms (p = 0.041) and the soleus and medial gastrocnemius EMG amplitudes increasing by 14–23% (p = 0.002–0.036) during the balance perturbation trials. While the magnitude of these results may suggest that foot cooling has a minor functional consequence on reactive postural control, it is likely that the results also reflect the ability of the central nervous system to rapidly adapt to situations with altered somatosensory feedback.     

Evidence of muscular adaptations within four weeks of barbell training in women

We investigated the time course of neuromuscular and hypertrophic adaptations associated with only four weeks of barbell squat and deadlift training. Forty-seven previously untrained women (mean ± SD, age = 21 ± 3 years) were randomly assigned to low volume training (n = 15), moderate volume training (n = 16), and control (n = 16) groups. The low and moderate volume training groups performed two and four sets, respectively, of five repetitions per exercise, twice a week. Testing was performed weekly, and included dual X-ray absorptiometry and vastus lateralis and rectus femoris B-mode ultrasonography. Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis and biceps femoris during isometric maximal voluntary contractions of the leg extensors. Significant increases in lean mass for the combined gynoid and leg regions for the low (+0.68 kg) and moderate volume (+0.47 kg) groups were demonstrated within three weeks. Small-to-moderate effect sizes were shown for leg lean mass, vastus lateralis thickness and pennation angle, and peak torque, but EMG amplitude was unaffected. These findings demonstrated rapid muscular adaptations in response to only eight sessions of back squat and deadlift training in women despite the absence of changes in agonist–antagonist EMG amplitude.     

Landing pattern and vertical loading rates during first attempt of barefoot running in habitual shod runners

There is evidence supporting that habitual barefoot runners are able to disperse impact loading rates by landing pattern modification. Yet, case studies suggested that barefoot running may result in severe running injuries, such as metatarsal and calcaneal stress fractures. Injuries may be due to a difference in biomechanical response between habitual and novice barefoot runners. This study investigated the initial effects of barefoot running in habitual shod runners in terms of landing pattern modification and vertical loading rates. Thirty habitual shod runners (mean age 25.5 ± 5.2 years; 18 men; with a minimum running mileage of 30 km per week for at least one year) ran on an instrumented treadmill at 10 km/h shod and barefoot in a randomized order. Vertical average (VALR) and instantaneous loading rates (VILR) were obtained by established methods. Landing pattern was presented as a ratio between the number of footfalls with a heelstrike and the total step number. Twenty participants demonstrated an automatic transition to a non-heelstrike landing during barefoot running, whereas a mixed landing pattern was observed in 10 participants. Compared to shod running, both VALR and VILR were significantly reduced during barefoot running (p < .021). In the subgroup analysis, VALR for the shod condition was significantly higher than barefoot running, regardless of the landing pattern. VALR for the non-heelstrike pattern during barefoot running was significantly lower than participants with a mixed landing pattern. Conversely, we observed two participants who completely altered their landing patterns, presented high VALR and VILR values. Habitual shod runners presented lower loading rates during barefoot running but their landing pattern transitions were not uniform. Novice barefoot runners with a mixed landing pattern may sustain higher loading rates, compared with those who completely avoided heelstrike pattern. However, a complete landing pattern modification may not guarantee lower loading rates.     

Evaluating feedback time delay during perturbed and unperturbed balance in handstand

Feedback delays in balance are often assessed using muscle activity onset latencies in response to discrete perturbations. The purpose of the study was to calculate EMG latencies in perturbed handstand, and determine if delays are different to unperturbed handstand. Twelve national level gymnasts completed 12 perturbed and 10 unperturbed (five eyes open and five closed) handstands. Forearm EMG latencies during perturbed handstands were assessed against delay estimates calculated via: cross correlations of wrist torque and COM displacement, a proportional and derivative model of wrist torque and COM displacement and velocity (PD model), and a PD model incorporating a passive stiffness component (PS-PD model). Delays from the PD model (161 ± 14 ms) and PS-PD model (188 ± 14 ms) were in agreement with EMG latencies (165 ± 14 ms). Cross correlations of COM displacement and wrist torque provided unrealistically low estimates (5 ± 9 ms). Delays were significantly lower during perturbed (188 ± 14 ms) compared to unperturbed handstand (eyes open: 207 ± 12 ms; eyes closed: 220 ± 19 ms). Significant differences in delays and model parameters between perturbed and unperturbed handstand support the view that balance measures in perturbed testing should not be generalised to unperturbed balance.     

Propulsion strategy in the gait of primary school children; the effect of age and speed

The strategy used to generate power for forward propulsion in walking and running has recently been highlighted as a marker of gait maturation and elastic energy recycling. This study investigated ankle and hip power generation as a propulsion strategy (PS) during the late stance/early swing phases of walking and running in typically developing (TD) children (15: six to nine years; 17: nine to 13 years) using three-dimensional gait analysis. Peak ankle power generation at push-off (peakA2), peak hip power generation in early swing (peakH3) and propulsion strategy (PS) [peakA2/(peakA2 + peakH3)] were calculated to provide the relative contribution of ankle power to total propulsion. Mean PS values decreased as speed increased for comfortable walking (p < 0.001), fast walking (p < 0.001) and fast running (p < 0.001), and less consistently during jogging (p = 0.054). PS varied with age (p < 0.001) only during fast walking. At any speed of fast walking, older children generated more peakA2 (p = 0.001) and less peakH3 (p = 0.001) than younger children. While the kinetics of running propulsion appear to be developed by age six years, the skills of fast walking appeared to require additional neuromuscular maturity. These findings support the concept that running is a skill that matures early for TD children.     

Leg and vertical stiffness (a)symmetry between dominant and non-dominant legs in young male runners

Biomechanical findings show that running is asymmetric in many kinetic properties. Running stiffness is a vital kinetic property of yet unknown pattern of lateralization. The aim of this study was to examine the degree and variability of lower limb dominance specific asymmetry of running in terms of leg stiffness, vertical stiffness, contact time, flight time, maximal ground reaction force during contact, vertical displacement of the center of mass, and change in leg length. Leg and vertical stiffness was estimated by the sine-wave method in 22 young males during treadmill running at 4.44 m/s. Lower limb dominance was determined by the triple-jump test. Asymmetry was expressed as dominant – non-dominant, and indexed by the absolute asymmetry index. Significant asymmetry was found only in flight time (3.98%) and in maximal ground reaction force (1.75%). The absolute asymmetry index ranged from 1.8% to 6.4%, showed high variation between subjects (0–31.6%), and differentiated among the 7 analyzed variables. Leg and vertical stiffness in treadmill running of moderate pace (4.44 m/s) should be considered symmetric.     

Slipping during side-step cutting: Anticipatory effects and familiarization

The aim of the present study was to verify whether the expectation of perturbations while performing side-step cutting manoeuvres influences lower limb EMG activity, heel kinematics and ground reaction forces. Eighteen healthy men performed two sets of 90° side-step cutting manoeuvres. In the first set, 10 unperturbed trials (Base) were performed while stepping over a moveable force platform. In the second set, subjects were informed about the random possibility of perturbations to balance throughout 32 trials, of which eight were perturbed (Pert, 10 cm translation triggered at initial contact), and the others were “catch” trials (Catch). Center of mass velocity (CoM_VEL), heel acceleration (H_AC), ground reaction forces (GRF) and surface electromyography (EMG) from lower limb and trunk muscles were recorded for each trial. Surface EMG was analyzed prior to initial contact (PRE), during load acceptance (LA) and propulsion (PRP) periods of the stance phase. In addition, hamstrings-quadriceps co-contraction ratios (CCR) were calculated for these time-windows. The results showed no changes in CoM_VEL, H_AC, peak GRF and surface EMG PRE among conditions. However, during LA, there were increases in tibialis anterior EMG (30–50%) concomitant to reduced EMG for quadriceps muscles, gluteus and rectus abdominis for Catch and Pert conditions (15–40%). In addition, quadriceps EMG was still reduced during PRP (p < .05). Consequently, CCR was greater for Catch and Pert in comparison to Base (p < .05). These results suggest that there is modulation of muscle activity towards anticipating potential instability in the lower limb joints and assure safety to complete the task.     

Neuromechanical synergies in single-leg landing reveal changes in movement control

Our purpose was to examine changes in single-leg landing biomechanics and movement control following alterations in mechanical task demands via external load and landing height. We examined lower-extremity kinematic, kinetic, and electromyographic (EMG) adjustments, as well as changes in movement control from neuromechanical synergies using separate principal component analyses (PCA). Nineteen healthy volunteers (15M, 4F, age: 24.3 ± 4.9 y, mass: 78.5 ± 14.7 kg, height: 1.73 ± 0.08 m) were analyzed among 9 single-leg drop landing trials in each of 6 experimental conditions (3 load and 2 landing height) computed as percentages of subject bodyweight (BW, BW + 12.5%, BW + 25%) and height (H12.5% & H25%). Condition order was counterbalanced, including: 1.) BW·H12.5, 2.) BW + 12.5·H12.5, 3.) BW + 25·H12.5, 4.) BW·H25, 5.) BW + 12.5·H25, 6.) BW + 25·H25. Lower-extremity sagittal joint angles and moments (hip, knee, & ankle), vertical ground reaction force (GRFz), and electrical muscle activity (gluteus maximus, biceps femoris, vastus medialis, medial gastrocnemius, & tibialis anterior muscles), were analyzed in each trial. Biomechanical adjustments and neuromechanical synergies were assessed using PCA. Subjects reduced effective landing height through segmental configuration adjustments at ground contact, extending at the hip and ankle joints with greater load and landing height (p ⩽ 0.028 and p ⩽ 0.013, respectively), while using greater medial gastrocnemius pre-activation with greater load (p ⩽ 0.006). Dimension reduction was observed under greater mechanical task demands, compressing and restructuring synergies among patterns of muscle activation, applied loads, and segmental configurations. These results provide insight into movement control and potential injury mechanisms in landing activities.     

Vertical and leg stiffness and stretch-shortening cycle changes across maturation during maximal sprint running

The purpose of this study was to investigate whether vertical and leg stiffness, and stretch-shortening cycle (SSC) ability differed in developing athletes of various maturity status during maximal sprint running. Seventy-four male participants between 8 and 16 years of age were categorized into pre-, mid- or post-peak height velocity (PHV) and sprinted for 30 meters on a non-motorized treadmill. Dimensionless vertical stiffness increased significantly (p < .05) from pre-, to mid- and post-PHV state, while dimensionless leg stiffness was significantly higher in post- compared to mid- (18.4%) and pre-PHV participants (44.5%). Eccentric power was significantly lower in pre- compared to the mid- and post-PHV participants. Concentric power increased from pre- to mid- and post-PHV state. An analysis of covariance revealed no significant differences between all groups in dimensionless vertical and leg stiffness, eccentric and concentric time and power when controlling for years from PHV (maturation). Eccentric or concentric power, were found to be the best predictors of maximum velocity across all maturation groups (r² = .37–.68). It seems that maturation affects the ability to absorb and produce power and furthermore these variables are important predictors of maximal running velocity.     

Kinematic and ground reaction force accommodation during weighted walking

Weighted walking is a functional activity common in daily life and can influence risks for musculoskeletal loading, injury and falling. Much information exists about weighted walking during military, occupational and recreational tasks, but less is known about strategies used to accommodate to weight carriage typical in daily life. The purposes of the study were to examine the effects of weight carriage on kinematics and peak ground reaction force (GRF) during walking, and explore relationships between these variables. Twenty subjects walked on a treadmill while carrying 0, 44.5 and 89 N weights in front of the body. Peak GRF, sagittal plane joint/segment angular kinematics, stride length and center of mass (COM) vertical displacement were measured. Changes in peak GRF and displacement variables between weight conditions represented accommodation. Effects of weight carriage were tested using analysis of variance. Relationships between peak GRF and kinematic accommodation variables were examined using correlation and regression. Subjects were classified into sub-groups based on peak GRF responses and the correlation analysis was repeated. Weight carriage increased peak GRF by an amount greater than the weight carried, decreased stride length, increased vertical COM displacement, and resulted in a more extended and upright posture, with less hip and trunk displacement during weight acceptance. A GRF increase was associated with decreases in hip extension (|r| = .53, p = .020) and thigh anterior rotation (|r| = .57, p = .009) displacements, and an increase in foot anterior rotation displacement (|r| = .58, p = .008). Sub-group analysis revealed that greater GRF increases were associated with changes at multiple sites, while lesser GRF increases were associated with changes in foot and trunk displacement. Weight carriage affected walking kinematics and revealed different accommodation strategies that could have implications for loading and stability.     

High- compared to low-arched athletes exhibit smaller knee abduction moments in walking and running

High- (HA) and low-arched athletes (LA) experience distinct injury patterns. These injuries are the result of the interaction of structure and biomechanics. A suggested mechanism of patellofemoral pain pertains to frontal plane knee moments which may be exaggerated in LA athletes. We hypothesize that LA athletes will exhibit greater peak knee abduction moments than high-arched athletes.MethodsTwenty healthy female recreational athletes (10 HA and 10 LA) performed five over-ground barefoot walking and five barefoot running trials at a self-selected velocity while three-dimensional kinematics and ground reaction forces were recorded. Peak knee abduction moments and time-to-peak knee abduction moments were calculated using Visual 3D.ResultsHigh-arched athletes had smaller peak knee abduction moments compared to low-arched athletes during walking (KAM1: p = 0.019; KAM2: p = 0.015) and running (p = 0.010). No differences were observed in time-to-peak knee abduction moment during walking (KAM1: p = 0.360; KAM2: p = 0.085) or running (p = 0.359).ConclusionsThese findings demonstrate that foot type is associated with altered frontal plane knee kinetics which may contribute to patellofemoral pain. Future research should address the efficacy of clinical interventions including orthotics and rehabilitation programs in these athletes.     

Reliability of forward head posture evaluation while sitting,standing, walking and running

Forward head posture has been evaluated mostly by visual observation or simple non-invasive measurements without a standardized evaluation method or protocol. In this experimental study, the reliability of existing forward head-posture measurement methods was evaluated by computing the intra-class correlation coefficients of three different head-position variables (two horizontal gap variables and one head-orientation variable) in seven different posture conditions from 20 asymptomatic participants. The position variables of the head were measured three times using a three-dimensional motion capture system while sitting comfortably, sitting with the back straight, standing comfortably, standing with the back straight, walking at 4 and 6 km/h on a treadmill, and running at 8 km/h on a treadmill. Intra-class correlation coefficients between repetitive measures ranged from 0.81 to 0.96, and high correlation coefficient values (>0.9) were produced when the head-position variables were measured during straight sitting, straight standing, and walking at 6 km/h. Among the three head-position variables, a horizontal gap between the tragus and the 7th cervical vertebra was recorded more consistently than other variables. Results of this study highlight the importance of a standardized evaluation protocol for more reliable assessment of the forward head posture.     

Effects of an activity-based anorexia procedure on within-session changes in nose-poke responding

This study tested the effects of an activity-based anorexia (ABA) procedure on within-session changes in responding. In the ABA group (N = 8), rats were given a 60-min feeding session and allowed to run in a running wheel for the remainder of each day. During the daily 60-min feeding session, each nose-poke response was reinforced by a food pellet. In the control group (N = 8), rats experienced the same procedure except that the wheel was locked and thus rats could not run. The experiment lasted for 6 days. Rats in the ABA group consumed less and lost more body weight than those in the control group. Within-session decreases in nose-poke responding were steeper for ABA than control rats. In addition, response rates were well described as linear functions of the cumulative number of reinforcers in both groups (r²s > .96). The regression lines for the ABA group had steeper slopes and smaller x-axis intercepts than those for the control group. However, the y-axis intercepts of the regression lines were similar for the two groups. These effects were different from the effects of taste-aversion learning induced by post-session wheel running (Aoyama, 2007), suggesting a different mechanism in each preparation.     

The effect of swinging the arms on muscle activation and production of leg force during ski skating at different skiing speeds

The study investigated the effects of arm swing during leg push-off in V2-alternate/G4 skating on neuromuscular activation and force production by the leg muscles. Nine skilled cross-country skiers performed V2-alternate skating without poles at moderate, high, and maximal speeds, both with free (SWING) and restricted arm swing (NOSWING). Maximal speed was 5% greater in SWING (P < 0.01), while neuromuscular activation and produced forces did not differ between techniques. At both moderate and high speed the maximal (2% and 5%, respectively) and average (both 5%) vertical force and associated impulse (10% and 14%) were greater with SWING (all P < 0.05). At high speed range of motion and angular velocity of knee flexion were 24% greater with SWING (both P < 0.05), while average EMG of m. biceps femoris was 31% lower (all P < 0.05) in SWING. In a similar manner, the average EMG of m. vastus medialis and m. biceps femoris were lower (17% and 32%, P < 0.05) during the following knee extension. Thus, swinging the arms while performing V2-alternate can enhance both maximal speed and skiing economy at moderate and, in particularly, high speeds.