A wireless accelerometer node for reliable and valid measurement of lumbar accelerations during treadmill running.

This study investigated the reliability of a wireless accelerometer and its agreement with optical motion capture for the measurement of root mean square (RMS) acceleration during running. RMS acceleration provides a whole-body metric of movement mechanics and economy. Fifteen healthy college-age participants performed treadmill running for two 60-s trials at 2.22, 2.78, and 3.33 m/s and one trial of 150 s (five 30-s epochs) at 2.78 m/s. We assessed between-trial and within-trial reliability, and agreement in each axis between a trunk-mounted wireless accelerometer and a reflective marker on the accelerometer measured by optical motion capture. Intraclass correlations assessing between-trial repeatability were 0.89-0.97, depending on the axis, and intraclass correlations assessing within-trial repeatability were 0.99-1.00. Bland-Altman analyses assessing agreement indicated mean difference values between -0.03 and 0.03 g, depending on the axis. Anterio-posterior acceleration had the greatest limits of agreement (LOA) (±0.12 g) and vertical acceleration had the smallest LOA (±0.03 g). For measuring RMS acceleration of the trunk, this wireless accelerometer node provides repeatable and valid measurement compared with the standard laboratory method of optical motion capture.

Contributions of lower extremity kinematics to trunk accelerations during moderate treadmill running.

BACKGROUND: Trunk accelerations during running provide useful information about movement economy and injury risk. However, there is a lack of data regarding the key biomechanical contributors to these accelerations. The purpose was to establish the biomechanical variables associated with root mean square (RMS) accelerations of the trunk. METHODS: Eighteen healthy males (24.0 ± 4.2 yr; 1.78 ± 0.07 m; 79.7 ± 14.8 kg) performed treadmill running with high resolution accelerometer measurement at the lumbar spine and full-body optical motion capture. We collected 60 sec of data at three speeds (2.22, 2.78, 3.33 m ∙ s(-1)). RMS was calculated for medio-lateral (ML), anterio-posterior (AP), vertical (VT), and the resultant Euclidean scalar (RES) acceleration. From motion capture, we calculated 14 kinematic variables, including mean sagittal plane joint angles at foot contact, mid-stance, and toe-off. Principal components analysis (PCA) was used to form independent components comprised of combinations of the original variables. Stepwise regressions were performed on the original variables and the components to determine contributions to RMS acceleration in each axis. RESULTS: Significant speed effects were found for RMS-accelerations in all axes (p < 0.05). Regressions of the original variables indicated from 4 to 5 variables associated with accelerations in each axis (R2 = 0.71 to 0.82, p < 0.001). The most prominent contributing variables were associated with the late flight and early stance phase. PCA reduced the data into four components. Component 1 included all hip angles before mid-stance and component 2 was primarily associated with propulsion. Regressions indicated key contributions from components 1 and 2 to ML, VT, and RES acceleration (p < 0.05). CONCLUSIONS: The variables with highest contribution were prior to mid-stance and mechanically relate to shock absorption and attenuation of peak forces. Trunk acceleration magnitude is associated with global running variables, ranging from energy expenditure to forces lending to the mechanics of injury. These data begin to delineate running gait events and offer relationships of running mechanics to those structures more proximal in the kinetic chain. These relationships may provide insight for technique modification to maximize running economy or prevent injury.

Lower extremity fatigue increases complexity of postural control during a single-legged stance.

BACKGROUND: Non-linear approaches to assessment of postural control can provide insight that compliment linear approaches. Control entropy (CE) is a recently developed statistical tool from non-linear dynamical systems used to assess the complexity of non-stationary signals. We have previously used CE of high resolution accelerometry in running to show decreased complexity with exhaustive exercise. The purpose of this study was to determine if complexity of postural control decreases following fatiguing exercise using CE. METHODS: Ten subjects (5 M/5 F; 25 ± 3 yr; 169.4 ± 11.7 cm; 79.0 ± 16.9 kg) consented to participation approved by Western Oregon University IRB and completed two trials separated by 2-7 days. Trials consisted of two single-legged balance tests separated by two Wingate anaerobic tests (WAnT; PreFat/PostFat), or rest period (PreRest/PostRest). Balance tests consisted of a series of five single-legged stances, separated by 30 s rest, performed while standing on the dominant leg for 15-s with the participant crossing the arms over the chest and flexing the non-dominant knee to 90 degrees. High resolution accelerometers (HRA) were fixed superficial to L3/L4 at the approximate center of mass (COM). Triaxial signals from the HRA were streamed in real time at 625 Hz. COM accelerations were recorded in g's for vertical (VT), medial/lateral (ML), and anterior/posterior (AP) axes. A newly developed statistic (R-test) was applied to group response shapes generated by Karhunen Loeve (KL) transform modes resulting from Control Entropy (CE) analysis. RESULTS: R-tests showed a significant mean vector difference (p < .05) within conditions, between axes in all cases, except PostFat, indicating the shape of the complexity response was different in these cases. R-test between conditions, within axis, differences were only present in PostFat for AP vs. PreFat (p < .05). T-tests showed a significantly higher overall CE PostFat in VT and ML compared to PreFat and PostRest (p < .0001). PostFat CE was also higher than PostRest in AP (p < .0001). CONCLUSIONS: These data indicate that fatiguing exercise eliminates the differential complexity response between axes, but increases complexity in all axes compared to the non-fatigued condition. This has implications with regard to the effects of fatigue on strategies of the control system to maintain postural control.

Reliability of mechanomyography and triaxial accelerometry in the assessment of balance.

Reliability of high-resolution accelerometery (HRA) and mechanomyography (MMG) was evaluated for the assessment of single-leg balance. Subjects (5M/5F, 25+/-3 yr; 169.4+/-11.7 cm; 79.0+/-16.9 kg) participated in fifteen (three randomized bouts of five repetitions) 15-s dominant leg stances. A single HRA was fixed superficial to L3/L4 segment to capture motions relative to the center-of-mass, and three-uniaxial accelerometers were fixed on the surface of the dominant leg correspondent to the vastus medialis (VM), vastus lateralis (VL), and soleus (SOL) muscles to record MMG. Triaxial signals from the HRA (s.r.=625 Hz) were streamed to a base station, simultaneously with MMG (s.r.=1000 Hz). Signals were sampled, recorded and later analyzed. HRAs were recorded in g's for vertical (VT), medial/lateral (ML), anterior/posterior (AP) directions, and resultant (RES) scalar. Intraclass correlation coefficients (ICC) were computed for each and Pearson's r was calculated for the relationships between MMG and HRA (alpha < or =0.05). Except for RES (ICC=0.36), all measures demonstrated moderately strong reliability (ICC=0.75, 0.73, 0.63, 0.87, 0.89, and 0.86 for VM, VL, SOL, VT, ML, and AP, respectively). HRA and MMG provide reliable information pertaining to balance, and may have application in evaluating postural control and stability.

High resolution MEMS accelerometers to estimate VO2 and compare running mechanics between highly trained inter-collegiate and untrained runners.

BACKGROUND: The purposes of this study were to determine the validity and reliability of high resolution accelerometers (HRA) relative to VO(2) and speed, and compare putative differences in HRA signal between trained (T) and untrained (UT) runners during treadmill locomotion. METHODOLOGY: Runners performed 2 incremental VO(2max) trials while wearing HRA. RMS of high frequency signal from three axes (VT, ML, AP) and the Euclidean resultant (RES) were compared to VO(2) to determine validity and reliability. Additionally, axial rms relative to speed, and ratio of axial accelerations to RES were compared between T and UT to determine if differences in running mechanics could be identified between the two groups. PRINCIPAL FINDINGS: Regression of RES was strongly related to VO(2), but T was different than UT (r = 0.96 vs 0.92; p<.001) for walking and running. During walking, only the ratio of ML and AP to RES were different between groups. For running, nearly all acceleration parameters were lower for T than UT, the exception being ratio of VT to RES, which was higher in T than UT. All of these differences during running were despite higher VO(2), O(2) cost, and lower RER in T vs UT, which resulted in no significant difference in energy expenditure between groups. CONCLUSIONS/SIGNFICANCE: These results indicate that HRA can accurately and reliably estimate VO(2) during treadmill locomotion, but differences exist between T and UT that should be considered when estimating energy expenditure. Differences in running mechanics between T and UT were identified, yet the importance of these differences remains to be determined.

Control entropy identifies differential changes in complexity of walking and running gait patterns with increasing speed in highly trained runners.

Regularity statistics have been previously applied to walking gait measures in the hope of gaining insight into the complexity of gait under different conditions and in different populations. Traditional regularity statistics are subject to the requirement of stationarity, a limitation for examining changes in complexity under dynamic conditions such as exhaustive exercise. Using a novel measure, control entropy (CE), applied to triaxial continuous accelerometry, we report changes in complexity of walking and running during increasing speeds up to exhaustion in highly trained runners. We further apply Karhunen-Loeve analysis in a new and novel way to the patterns of CE responses in each of the three axes to identify dominant modes of CE responses in the vertical, mediolateral, and anterior/posterior planes. The differential CE responses observed between the different axes in this select population provide insight into the constraints of walking and running in those who may have optimized locomotion. Future comparisons between athletes, healthy untrained, and clinical populations using this approach may help elucidate differences between optimized and diseased locomotor control.

Effects of balance training on selected skills.

The purpose of this study was to determine the effect of a 4-week balance training program on specified functional tasks. Thirty-six subjects (age = 22.7 +/- 2.10 years; height = 168.30 +/- 9.55 cm; weight = 71.15 +/- 16.40 kg) were randomly placed into control (C; n = 19) and experimental groups (Tx; n = 17). The Tx group trained using a commercially available balance training device (BOSU). Postural limits (displacement and sway) and functional task (time on ball, shuttle run, and vertical jump) were assessed during a pretest (T1), a posttest (T2), and 2 weeks posttraining (T3). Multivariate repeated measures analysis (alpha = 0.05) revealed significant differences in time on ball, shuttle run, total sway, and fore/aft displacement after the exercise intervention (T2). T3 assessment revealed that total sway and time on ball remained controlled; however, no other measures were retained. Balance training improved performance of selected sport-related activities and postural control measures, although it is unclear whether the effect of training would transfer to general functional enhancement.

Effects of pelvic stabilization on lumbar muscle activity during dynamic exercise.

Many commonly utilized low-back exercise devices offer mechanisms to stabilize the pelvis and to isolate the lumbar spine, but the value of these mechanisms remains unclear. The purpose of this study was to examine the effect of pelvic stabilization on the activity of the lumbar and hip extensor muscles during dynamic back extension exercise. Fifteen volunteers in good general health performed dynamic extension exercise in a seated upright position on a lumbar extension machine with and without pelvic stabilization. During exercise, surface electromyographic activity of the lumbar multifidus and biceps femoris was recorded. The activity of the multifidus was 51% greater during the stabilized condition, whereas there was no difference in the activity of the biceps femoris between conditions. This study demonstrates that pelvic stabilization enhances lumbar muscle recruitment during dynamic exercise on machines. Exercise specialists can use these data when designing exercise programs to develop low back strength.

Adaptive sweat gland response after spinal cord injury.

OBJECTIVE: To compare the eccrine gland cholinergic sensitivity of upper (UE) and lower (LE) extremities in untrained able-bodied individuals (UAB), untrained individuals with spinal cord injury (U/SCI), and trained wheelchair athletes (E/SCI). DESIGN: Static group comparison. SETTING: SCI population. PARTICIPANTS: A total of 25 men (mean age, 27.8+/-5.0 y; mean height, 175.8+/-9.1cm; mean weight, 76.2+/-7.7 kg) were categorized into 3 groups UAB (n=10), U/SCI (n=10), and E/SCI (n=5). Individuals with SCI had injuries ranging from C4-8. INTERVENTIONS: Peripheral sweat production was induced by using pilocarpine iontophoresis at surface landmarks relative to the flexor carpi radialis and medial gastrocnemius muscles. MAIN OUTCOME MEASURES: Peripheral sweat rate (SR), sweat gland density (SGD), and sweat per gland (S/G) were calculated for both UE and LE. RESULTS: Peripheral SR for the UAB in both UE (7.58+/-1.99 g x m(-2) x min(-1)) and LE (4.42+/-1.23 g x m(-2) x min(-1)) were significantly greater than those for U/SCI (1.08+/-1.01 g x m(-2) x min(-1), .24+/-.35 g x m(-2) x min(-1), respectively) and E/SCI (3.61+/-2.1 g x m(-2) x min(-1),.71+/-.81 g x m(-2). min(-1), respectively). Furthermore, the UE versus LE SR ratio was calculated at 1.71:1 for UAB subjects, whereas U/SCI and E/SCI subjects showed a ratio of 4.50:1 and 5.07:1, respectively. UE SGD measures in U/SCI (83.20+/-39.84 glands/cm(2)) persons were significantly less than either the UAB (120.20+/-21.42 glands/cm(2)) or the E/SCI (120.80+/-21.56 glands/cm(2)). CONCLUSIONS: These results may indicate that sweat glands below the lesion are less sensitive to cholinergic activation, regardless of central or exogenous stimulation. However, glands above the level of the lesion may exhibit increased productivity when individuals are exposed to physical training and physiologic stress.

Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits.

OBJECTIVE: To quantify changes in balance parameters and ranges of postural control at the ankle after isokinetic fatigue. DESIGN: Before-after trials, with a 5 x 6 repeated-measures design. SETTING: General community. PARTICIPANTS: Twenty-four men (age, 24.9 +/- 3.92y; height, 177.79 +/- 6.36cm; weight, 80.78 +/- 13.22kg) without ankle trauma within 2 years. INTERVENTIONS: Fatigue of the plantarflexors and dorsiflexors was induced by isokinetic contractions. Balance was assessed by using a unilateral test (15-s quiet stance, 10-s lean test) on a force platform immediately before and at 0 (T0), 10 (T10), 20 (T20), and 30 (T30) minutes postfatigue. MAIN OUTCOME MEASURE: Mediolateral (ML) and fore-aft (FA) sway as well as ML and FA displacement were analyzed by analysis of variance with repeated measures for time (alpha =.05). RESULTS: In quiet stance, ML sway was greater at T0, whereas total sway increased at all time points postfatigue (P < .05). For the lean test, FA sway increased at T0 and T10, and total sway increased at all time points (P < .05). Both ML and FA displacement significantly differed at T0 (P < .05). All sway parameters returned to baseline within 20 minutes. CONCLUSIONS: Isokinetic fatigue of ankle plantarflexors and dorsiflexors significantly influences sway parameters and ranges of postural control in healthy young men. These perturbations are transient, and recovery occurs within 20 minutes.