Effects of a Total Motion Release (TMR®) Protocol for the Single Leg Squat on Asymmetrical Movement Patterns.

BACKGROUND: Improving single leg squat (SLS) movement symmetry may benefit rehabilitation protocols. The Total Motion Release® (TMR®) protocol has been theorized to evaluate and improve patient-perceived movement asymmetries. HYPOTHESIS/PURPOSE: The purpose of this study was to evaluate whether perceived asymmetries identified by a TMR® scoring protocol were related to biomechanical asymmetries and whether improving perceived asymmetries influenced movement mechanics. It was hypothesized that participants with perceived asymmetries would also present with biomechanical asymmetries. A secondary hypothesis was that participants would reduce their perceived asymmetries after performing the TMR® protocol and subsequently have greater biomechanical symmetry. STUDY DESIGN: Descriptive Cohort (Laboratory Study). METHODS: Twenty participants (10 female, 10 male) with self-identified bilateral differences of 10 points or greater on the TMR® scoring scale were recruited for the study. The non-preferred side was defined as the side that scored higher. 3Dimensional motion capture was used to bilaterally assess baseline SLS depth as well as hip, knee, and ankle kinematics and kinetics. For the TMR® protocol, sets of 10 SLSs were performed on the preferred leg until their perceived asymmetries were resolved (i.e., both sides scored equally), or four sets had been completed. Kinematics and kinetics were collected immediately after the intervention and after a 10-minute rest period. RESULTS: Participants had biomechanical asymmetries at baseline for knee flexion, ankle flexion, and knee moments. Following the intervention, participants had reduced TMR® scores on the non-preferred leg, and this coincided with increased knee joint moments on that side. Although perceived asymmetries were resolved after the intervention, kinematic and kinetic asymmetries at the knee and ankle were still present. CONCLUSIONS: A TMR® intervention could benefit rehabilitation protocols by reducing factors of dysfunction and increasing the ability of patients to load the non-preferred knee. Further investigations are necessary to elucidate the importance of asymmetrical movement patterns. LEVEL OF EVIDENCE: 3b.

Walking Kinematic Coordination Becomes More In-Phase at Extreme Inclines.

Previous research has shown that there are differences in mechanical energy, kinematics, and muscle activation when comparing walking on level and incline surfaces, especially on inclines above 15%. Muscle activations are significantly different while walking on extreme inclines, suggesting a different coordination pattern. We utilized continuous relative phase to assess walking kinematic coordination with respect to increased incline angles. Twelve healthy, college-aged individuals walked for 7 inclines of 1 minute each on a motorized treadmill at 3 mph at 0%, 5%, 10%, 15%, 20%, 25%, and 30% inclines. Kinematic data were collected during the last 20 seconds of each stage (120 Hz). Segmental and joint angles and angular velocities in the sagittal plane were calculated, from which continuous relative phase was determined for 3 joint couples: hip-knee, hip-ankle, and knee-ankle. There were significant differences in the coordination patterns during the first part of the contact phase in the hip-knee and hip-ankle couplings between the 0% and 30% inclines, with all 3 joint couplings becoming more in-phase at inclines above 15%. Importantly, the hip-knee coupling changed significantly from more out-of-phase to more in-phase between 10% and 15% incline. Shifting lower-extremity joint coordination in response to extreme inclines identifies potential coordinative strategies to achieve steep walking.

Examining movement asymmetries during three single leg tasks using interlimb and single subject approaches.

PURPOSE: s: To examine whether healthy individuals displayed asymmetric trunk and lower extremity kinematics in the frontal and sagittal planes using both interlimb and single subject models. METHODS: Trunk, pelvis, and lower extremity kinematic waveforms were analyzed bilaterally during the single leg squat (SLS), forward step down (FSD), and lateral step down (LSD). Participants identified task specific preferred and non-preferred legs based on perceived stability for interlimb analyses. Movement patterns were also analyzed with a single subject approach that included Fisher's exact tests to assess whether asymmetries were related to the task. RESULTS: Participants were found to have increased pelvic drop on the non-preferred leg during the LSD from 41 to 77% of the movement (p = 0.01). No other bilateral differences were found for interlimb analyses. Single subject analyses indicated that no task had a greater probability of finding or not finding asymmetries. Associations were found between the FSD and SLS for frontal plane hip (p < 0.01) and knee motion (p < 0.01). CONCLUSIONS: Interlimb analyses can be influenced by intraparticipant movement variability between preferred and non-preferred legs. Movement asymmetries during single leg weightbearing are likely task dependent and a battery of tests is necessary for assessing bilateral differences.

Differences in lower extremity joint stiffness during drop jump between healthy males and females.

The primary purpose of this study was to examine sex differences in lower extremity joint stiffness during vertical drop jump performance. A secondary purpose was to examine the potential influence of sex on the relationship between joint stiffness and jump performance. Thirty healthy and active individuals performed 15-drop jumps from 30 and 60 cm boxes. Hip, knee, and ankle joint stiffnesses were calculated for subphases of landing using a 2nd order polynomial regression model. Males had greater hip stiffness during the loading phase in drop jumps from both box heights than females' drop jump from 60 cm box. Also, males had a greater ground reaction force at the end of eccentric phase, net jump impulse, and jump height regardless of box height. The 60 cm box height increased knee stiffness during the loading phase, but reduced hip stiffness during the loading phase and knee and ankle stiffness during the absorption phase regardless of sex. Joint stiffnesses significantly predicted drop jump height for females (p < .001, r2 = 0.579), but not for males (p = .609, r2 = -0.053). These results suggest that females may have different strategies to maximize drop jump height as compared to males.

Upper extremity kinematics during walking gait changes through pregnancy.

BACKGROUND: Thirty percent of adults in the United States use wearable fitness devices as of 2020 [1], such as fitness watches, to monitor and track health and physical activity parameters. Physical changes during pregnancy may impact wrist worn device accuracy. The arms may be needed as compensation during walking because thorax axial rotation may be inhibited by pelvic tilt during pregnancy [2]. METHODS: To examine arm motion changes, twenty-three pregnant women (28 ± 4 y) were tested in four-week intervals ( ± 2 weeks) at 18-, 22-, 26-, 30- and 34-weeks' gestation. Kinematic data were measured during self-selected speed walking. Segment angles and angular velocities were analyzed over time. Linear regressions were used to analyze the correlations between arm motion and the other kinematic variables. RESULTS: Arm range of motion significantly increased (p = 0.006) over gestation, but leg, thorax, and pelvis range of motions did not significantly change. Arm range of motion was correlated with pelvis (r2 =0.311, p = 0.001, ß = 1.724) and leg (r2 = 0.285, p = 0.004, ß = 1.520) range of motion and gait velocity (r2 =0.566, p = 0.001, ß = 39.110). Arm velocities significantly increased (p < 0.012), as did leg velocities (p < 0.022) over gestation time, but thorax and pelvis rotational velocities did not significantly change over time. Arm velocity was correlated with leg velocity in both flexion (r2 =0.598, p = 0.001, ß = 1.61) and extension (r2 =0.568, p = 0.001, ß = 1.35). SIGNIFICANCE: Arm swing increases over the course of gestation during walking, which does not follow the exact pattern of changes seen in the legs, thorax, and pelvis. These results show that a typical gait analysis of lower body motions may miss important biomechanical changes or compensations at different points over pregnancy. Future studies should examine why these changes may occur. Studies should also be conducted to see if arm changes impact outcome parameters from fitness watches and affect their validity as an exercise tracker during pregnancy.

The Relationship Between Health and Movement Screens and Field-Based Physical Fitness Tests in Reserve Officer Training Corps Students.

The purpose of the present study was to evaluate the relationship between scores achieved in physical fitness tests and outcomes of health and movement screens (HMS) in ROTC students. Twenty-eight students (20 males: 21.8 yrs [± 3.4] & 8 females: 20.7 yrs [± 1.8]) enrolled in an ROTC branch (Army, Air Force, Navy, or Marines) completed a series of screens, including body composition analysis via Dual-Energy X-Ray Absorptiometry (DXA), balance and functional movement tasks via a lower-quarter Y-Balance test, and knee and hip joint concentric strength testing on an isokinetic dynamometer. Official ROTC PFT scores were collected from the respective military branch leadership. HMS outcomes were compared to PFT scores via Pearson Product-Moment Correlation and linear regression analyses. Across branches, total PFT scores were significantly correlated to visceral adipose tissue (r = -0.52, p = 0.01) and android:gynoid fat ratio (r = -0.43, p = 0.04). Visceral adipose tissue (R 2 = 0.27, p = 0.011) and android to gynoid ratio (R 2 = 0.18, p = 0.042) significantly predicted total PFT scores. No further significant correlations between HMS and overall PFT scores were observed. HMS scores revealed significant bilateral differences in lower extremity body composition (p < 0.001; d = 0.23) and strength (p = 0.002; d = 0.23). Across ROTC branches, HMS were poorly correlated with PFT performance yet indicated significant bilateral differences in lower extremity strength and body composition. The inclusion of HMS may ease the increasing injury rate among the military population by assisting in detection of movement shortcomings.

Creatine monohydrate supplementation changes total body water and DXA lean mass estimates in female collegiate dancers.

Collegiate dance is unique because it requires athletic and academic performance; therefore, optimizing physical and mental function is crucial. Research among athletic populations demonstrate improvements in body composition, performance, and cognition following creatine monohydrate (CR) supplementation, yet dancers have not been investigated. The purpose of this study was to determine the effects of CR supplementation on body composition, performance, and cognitive function in female collegiate dancers. Participants were randomized to CR (CR; n = 7; 0.1 g·kg -1·day -1 CM +0.1 g·kg -1·day -1 corn-starch maltodextrin) or placebo (PL; n = 6; 0.2 g·kg -1·day -1 corn-starch maltodextrin) for 42 days. Pre- and post-testing included body composition, total body water (TBW), Depression, Anxiety and Stress Scale, Diet History Questionnaire, the National Institute of Health Toolbox fluid cognition battery and isokinetic strength, vertical jump, medicine ball throw, and Wingate anaerobic power test. CR demonstrated a significant increase in TBW (pre, 32.2 ± 3.5 kg; post, 32.7 ± 3.6 kg; p = 0.024) and lean mass (LM; pre, 39.8 ± 3.6 kg; post, 41.5 ± 4.5 kg; p = 0.020). CR supplementation may be an effective strategy to increase TBW and estimates of LM in female collegiate dancers. Although this may optimize aesthetics, larger samples sizes with resistance training are needed to determine if CR supplementation increases muscle mass and translates to improved performance.

The Effect of Foot Position and Lean Mass on Jumping and Landing Mechanics in Collegiate Dancers.

The purpose of this study was to investigate the effects of foot positioning and lean mass on jumping and landing mechanics in collegiate dancers. Thirteen dancers performed 3 unilateral and bilateral vertical jumps with feet in neutral and turnout positions. Dual-energy x-ray absorptiometry scans, jump height, vertical stiffness, and joint stiffness were assessed for relationships between foot positions. Jump heights were greater in right compared with left limb (P = .029) and neutral compared with turnout (P = .020) during unilateral jumping. In unilateral landing, knee stiffness was greater in turnout compared with neutral (P = .004) during the loading phase. Jump height (P < .001) was significantly increased, and vertical stiffness (P = .003) was significantly decreased during bilateral jumping in neutral compared with turnout. Significantly increased hip stiffness during the attenuation phase was observed in neutral compared with turnout (P = .006). Left-limb lean mass was significantly less than the right limb (P < .05). Adjustments for bilateral jumping were focused on hip stiffness, whereas there was a slight shift to knee strategy for unilateral jump.

Lower Extremity Kinematic Waveform Analysis During a Single Leg Drop Task - Including a Single Subject Design.

BACKGROUND: Lower limb asymmetries may be associated with increased injury risk in an active female population. However, an appropriate method for determining these asymmetries has not been established. HYPOTHESIS/PURPOSE: The purpose of the present study was to examine the single leg drop landing (SLD) kinematic waveforms of female recreational athletes for the pelvis, hip, and knee using statistical parametric mapping (SPM). It was hypothesized that individual bilateral differences would be masked by the group analysis. STUDY DESIGN: Descriptive Laboratory Study. METHODS: The current study examined the sagittal and frontal plane pelvis, hip, and knee kinematics of nine physically active females during a SLD. To better elucidate whether asymmetries were present between right and left limbs throughout the landing phase, data were analyzed with SPM. The time-series data were comprised from initial contact to the bottom of the landing. A single subject design was also included to account for potential interindividual variability. RESULTS: At the group level there were no statistical differences between the right and left limbs of participants for all variables. The single subject design yielded at least two significant asymmetries for all participants. Six out of the nine participants had bilateral differences for all six kinematic time-series. CONCLUSIONS: The lack of significant differences at the group level may have been masked by movement variability amongst participants. For example, when considering participants with significant differences for hip flexion, four participants had greater values on the left limb and three on the right. A similar observation was made for knee flexion where three participants had significantly greater kinematic values on the left versus four on the right. Until a method is developed to adequately dichotomize lower extremities during the SLD task, a single subject design strategy be used with group analysis when making bilateral comparisons. LEVEL OF EVIDENCE: 3.

Application of Polynomial Regression Model for Joint Stiffness.

Quasi-stiffness (joint stiffness) is often used to characterize leg properties during athletic and other activities and has been reported by a single slope of angle-moment curve. However, the joint angle-moment relationship of some relationship are not effectively represented by a simple linear regression model. Thus, the purpose of this analysis was to investigate the benefits of utilizing a 2nd order polynomial regression (quadratic) model as compared to the linear model when calculating lower extremity joint stiffness incorporating subdivided eccentric phases. Thirty healthy and active college students performed 15 drop jumps from a 30-cm platform. The eccentric phase was identified as the time from initial foot contact (IC) to the lowest vertical position of the center of mass and subdivided into the loading and attenuation phases, separated by the peak vertical ground reaction force. Lower extremity joint stiffnesses (hip, knee, and ankle) for the loading and attenuation phases were calculated using a linear and quadratic model. Multiple 2 by 2 repeated measures ANOVAs were performed. In the post-hoc analyses, the quadratic model had greater goodness-of-fit (r 2 and RMSE) than the linear model (p < .05) for all joints. The quadratic model revealed differences between the loading and attenuation phases for both hip (p = .001) and knee stiffness (p < .001). These results suggest that the quadratic model is more representative of the angle-moment relationship while subdividing the eccentric phase of a drop jump into the loading and attenuation phases.

Sex and Limb Differences in Lower Extremity Alignment and Kinematics during Drop Vertical Jumps.

Sex and limb differences in lower extremity alignments (LEAs) and dynamic lower extremity kinematics (LEKs) during a drop vertical jump were investigated in participants of Korean ethnicity. One hundred healthy males and females participated in a drop vertical jump, and LEAs and LEKs were determined in dominant and non-dominant limbs. A 2-by-2 mixed model MANOVA was performed to compare LEAs and joint kinematics between sexes and limbs (dominant vs. non-dominant). Compared with males, females possessed a significantly greater pelvic tilt, femoral anteversion, Q-angle, and reduced tibial torsion. Females landed on the ground with significantly increased knee extension and ankle plantarflexion with reduced hip abduction and knee adduction, relatively decreased peak hip adduction, knee internal rotation, and increased knee abduction and ankle eversion. The non-dominant limb showed significantly increased hip flexion, abduction, and external rotation; knee flexion and internal rotation; and ankle inversion at initial contact. Further, the non-dominant limb showed increased peak hip and knee flexion, relatively reduced peak hip adduction, and increased knee abduction and internal rotation. It could be suggested that LEAs and LEKs observed in females and non-dominant limbs might contribute to a greater risk of anterior cruciate ligament injuries.

The construction of common treadmills significantly affects biomechanical and metabolic variables.

Surface compliance has been shown to affect leg stiffness and energetics. It is unknown if compliance differences between common treadmills would elicit such changes. Therefore, the purpose of this study was to determine if compliance design differences of common treadmills would affect the mechanics and energetics of running. Eleven runners ran at moderate, self-selected, matched belt speeds for three minutes on two treadmills: compliant (CT) and rigid (RT) decks. During the last minute of each trial, oxygen consumption and six markers describing the torso, thigh, shank and foot, and one marker to determine treadmill deflection were recorded. Leg stiffness, continuous relative phase (CRP) and CRP variability were calculated. Compared to RT, running on CT resulted in a significantly more compliant leg (8.591 kN•m-1 > 9.063 kN•m-1), lower oxygen consumption (34.69 ml•kg-1•min-1 < 36.86 ml•kg-1•min-1), different coordination patterns and greater variability, particularly during the push-off phase. These results are inconsistent with the literature because the deck of CT rebounds back at the runner during the absorption phase and away from the runner during the push-off phase. Therefore, care should be taken when using treadmills for research and comparing mechanical and energetic measures between studies.

Correlations between joint kinematics and dynamic balance control during gait in pregnancy.

BACKGROUND: Dynamic balance control degrades during pregnancy, but it is not yet understood why. Mechanical aspects of the body should directly affect walking balance control, but we have recently published papers indicating that weight gains during pregnancy explain very little dynamic balance changes. Our goal was to determine if lower extremity joint kinematic changes are an indicator of walking balance control. This information is vital to understanding the route by which pregnancy increases fall risk. METHODS: Twenty-three pregnant women were tested at five different times in the 2nd and 3rd trimesters of pregnancy. Participants performed walking trials at a self-selected pace. Motion capture was used to measure joint kinematics (discrete and coordination variables) and body center of mass motion. Changes over time were statistically analyzed. Correlations between kinematics and walking balance were modelled with hierarchical multiple regression models. RESULTS: As pregnancy progresses, it appears that a more flexed hip posture could be driving lower extremity kinematic changes toward increased coordination between joints and increased knee and ankle motions. Walking balance changes were also detected through increased COM motion (lateral range of motion and velocity) in the lateral directions. However, there was little correlation between kinematic and balance changes (r2 < 0.4). Strong correlations were only observed when all kinematics (including those that don't ubiquitously change during pregnancy) were used in the regression model (r2 > 0.7). SIGNIFICANCE: Our findings suggest that walking balance control is not altered by a common kinematic change between all pregnant women. While increased lateral center of mass motion should be expected with pregnancy, the kinematics leading to this increase may be person-specific. The cause of dynamic imbalance in each pregnant women (physiological, mechanical, and neurocognitive) may play an important role in determining the kinematic means by which lateral center of mass motion increases.

Understanding the influence of perceived fatigue on coordination during endurance running.

During the course of a training programme, runners will typically increase running velocity and volume possibly encountering fatigue during a run, which is characterised as a feeling of general tiredness. The purpose of the current study was to identify whether or not level of perceived fatigue affects coordination and coordination variability in healthy runners during the recovery velocity of an endurance interval run. A total of 20 endurance runners completed a 1-hour run that included running velocity intervals at 75% of estimated 10 k race pace (5 minutes) and estimated 10 k race pace (1 minute). After each run, participants completed a fatigue questionnaire and were grouped based on their post-run self-reported perceived fatigue. 3D motion capture data were collected during the run and analysed to generate coordination patterns and variability of the patterns as dependent variables. Multiple mixed model ANOVAs were conducted to test for differences between perceived fatigue groups. Coordination and variability differences were reported in a number of couplings during transition phases (late and early stance) and events (toe-off and foot contact) of the gait cycle. It was concluded that the level of perceived fatigue affected coordination and coordination variability during the recovery velocity of a 1-hour interval run.

Stand-to-sit kinematic changes during pregnancy correspond with reduced sagittal plane hip motion.

BACKGROUND: The stand-to-sit motion has been linked to falls during pregnancy. It is also used in the clinical evaluation of functional performance. The physical and physiological changes during pregnancy may necessitate a change in stand-to-sit kinematic performance. Therefore, this study was conducted to evaluate the longitudinal changes to stand-to-sit kinematics during pregnancy. METHODS: Fifteen pregnant women were tested in 4-week intervals from 16 weeks to 36 weeks gestational age. They performed a 60-second trial of semi-continuous stand-to-sit motion. Sagittal plane motions at the ankle, knee, spine, and shoulders were measured. Additionally, three-dimensional hip motion was measured. Discrete variables (e.g. range of motion) and joint coordinations (through vector coding) were analyzed over time through a linear mixed model analysis. FINDINGS: The results indicate a shift away from sagittal hip motion throughout pregnancy. Hip range of motion and standing angle changed in favor of spine motion. Joint coordination shifted from hip dominant to spine- and shoulder-dominate coordination just before the start of sitting motion. Hip-knee joint coordination just before seat contact shifted from hip to a knee-dominant motion during pregnancy. INTERPRETATION: Discrete variable changes in the entire stand-to-sit motion seem to be driven by initial standing posture related to an increase in gestational lordosis. Likewise, standing joint coordination shift to upper body motion can be attributed to gestational lordosis limiting functional ability around the hip. The shift in motion away from the hip may provide insight into why both fall rates and low back pain rates increase during stand-to-sit during pregnancy.

Effects of treadmill running velocity on lower extremity coordination variability in healthy runners.

With a growing interest in coordination variability and its role in endurance running, it is important to identify the effect of running velocity. The purpose of the current study was to investigate the effect of treadmill running velocity on the coordination and variability of coordination of lower extremity couplings of healthy runners during stance. Fourteen apparently healthy runners ran on a split-belt force instrumented treadmill at five different velocities. Continuous relative phase (CRP) was used to quantify coordination and variability (vCRP) between lower extremity couplings of the right limb (thigh-shank, thigh-foot, shank-foot) during three phases of stance (loading, mid stance, and propulsion). Multiple one-way repeated measure ANOVAs were conducted to identify differences among velocity conditions at each phase and discrete events (initial foot contact, peak knee flexion during stance, and toe-off). Thigh internal/external rotation (IR/ER)-Shank abduction/adduction (AB/AD) coupling was different during the propulsive phase (p = 0.02). Thigh flexion/extension-Shank flexion/extension showed the greatest differences in vCRP across velocity conditions with differences occurring during loading phase, mid stance, propulsive phase, and peak flexion (p < 0.05). Additionally, significant differences were seen in Thigh FL/EX-Shank FL/EX (toe-off, p = 0.01) and Thigh FL/EX-Foot inversion/eversion (IN/EV) (toe-off, p = 0.032). Interestingly, the decreases in vCRP values were accompanied by changes in center of mass vertical motion during stance, but not knee flexion angles. Increases in running velocity led to a more constrained running pattern through a reduction in degrees of freedom.

Adaptations of lumbar biomechanics after four weeks of running training with minimalist footwear and technique guidance: Implications for running-related lower back pain.

OBJECTIVES: To investigate the changes in lumbar kinematic and paraspinal muscle activation before, during, and after a 4-week minimalist running training. DESIGN: Prospective cohort study. SETTING: University research laboratory. PARTICIPANTS: Seventeen habitually shod recreational runners who run 10-50 km per week. MAIN OUTCOME MEASURES: During stance phases of running, sagittal lumbar kinematics was recorded using an electrogoniometer, and activities of the lumbar paraspinal muscles were assessed by electromyography. Runners were asked to run at a prescribed speed (3.1 m/s) and a self-selected speed. RESULTS: For the 3.1 m/s running speed, significant differences were found in the calculated mean lumbar posture (p = 0.001) during the stance phase, including a more extended lumbar posture after minimalist running training. A significant reduction in the contralateral lumbar paraspinal muscle activation was also observed (p = 0.039). For the preferred running speed, similar findings of a more extended lumbar posture (p = 0.002) and a reduction in contralateral lumbar paraspinal muscle activation (p = 0.047) were observed. CONCLUSION: A 4-week minimalist running training program produced significant changes in lumbar biomechanics during running. Specifically, runners adopted a more extended lumbar posture and reduced lumbar paraspinal muscle activation. These findings may have clinical implications for treating individuals with running-related lower back pain.

Muscle activity during backward and forward running with body weight support.

We investigated muscle activity during backward (BR) and forward (FR) running with body weight support (BWS). Ten participants completed BR and FR on a lower body positive pressure treadmill while selecting a preferred speed (PS) for different BWS conditions (0%, 20%, 40%, 60%, and 80%BWS). Muscle activity from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GA), rating of perceived exertion (RPE), preferred stride frequency (PSF), and PS were measured. Magnitude of muscle activity (BF, TA, and GA), RPE, PSF, and PS were not influenced by the interaction of direction and BWS (P>0.05). BF, TA, and GA were not different between directions (P>0.05) but were different between BWS conditions (P<0.01). RF was influenced by the interaction of direction and BWS (P<0.01). RF, BF, TA, and GA during BR were lower with increasing BWS. RF during BR was 59-86% higher than that of FR within BWS condition. RPE was lower with increasing BWS (P<0.001), regardless of direction of locomotion. PSF was lower and PS was higher during BR and FR with increasing BWS (both P<0.001). PSF during BR was 6-9% higher than that of FR. PS during BR was 24-31% lower than that of FR. These observations demonstrate that a change in BWS influences magnitude of muscle activity, PS, PSF, and RPE for both BR and FR. However, a change in direction of locomotion may not influence magnitude of muscle activity or RPE during running for a given BWS, even though muscle activity pattern, PS, and PSF were different between BR and FR.

Determining if muscle activity is related to preferred stride frequency during running in the water and on land.

PURPOSE: To determine if muscle activity is related to preferred stride frequency (PSF) during deep water running (DWR) and treadmill running on dry land (TMR). METHODS: Subjects (n = 11; 26.2 ± 4.4 years) completed TMR and DWR at their mode-specific preferred stride frequency (PSF mode). They also ran at stride frequencies which were lower and higher than the PSF mode (i.e., PSF mode ± 5, 10, and 15 %). Muscle activity from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GL), SF, and rating of perceived exertion (RPE) were measured. RESULTS: The PSF mode during DWR was significantly lower than that of TMR (i.e., 49.9 ± 11.0 versus 81.9 ± 4.8 strides/min, P < 0.0001). Additionally, muscle activity from the RF, TA, and GL during DWR was significantly lower than during TMR at respective PSF mode (~83.6 % decrease, P < 0.0001). However, RPE while running at the PSF mode during DWR and TMR was similar. During DWR, the RF, TA, and GL muscle activity was not different between PSF mode and any other SF conditions (P > 0.0005). During TMR, there was no significant difference in the RF and GL muscle activity between PSF mode and any other SF conditions during TMR (P > 0.0005). CONCLUSIONS: During DWR, subjects selected a lower PSF than during TMR even though RPE was the same. It was also determined that the relationship between muscle activity and changes in SF relative to the PSF mode was unique during DWR and TMR.