Tummy Time Tracking: Examining Agreement Between Parent Recall and Direct Observation in Infants.

IMPORTANCE: Parent recall is the primary method for measuring positioning practices such as tummy time in infants. Concerns regarding the accuracy of parent recall have been raised in the literature. To date, no study has examined the agreement of tummy time recall measures with gold-standard methods. OBJECTIVE: To assess the agreement between parental recall versus direct observation of tummy time in infants, and to explore the impact of prematurity on this relationship. DESIGN: Cross-sectional observational study, spanning 1 yr. SETTING: Participants' homes Participants: Thirty-two infant-parent dyads (19 full-term, 13 preterm), with infants ages 3 to 6 mo and caregivers ages older than 18 yr. OUTCOME AND MEASURES: Home-recorded videos of infant play across 3 days were used as a proxy for direct observation of tummy time and compared with a 12-item parent recall survey. RESULTS: Parent recall had a significant moderate correlation (ρ = .54, p = .002) with direct observation in full-term infants but was not correlated (p = .23) with direct observation in preterm infants. On average, parents of preterm infants overestimated tummy time by 2.5 times per day compared with direct observation. CONCLUSIONS AND RELEVANCE: For full-term infants, parent recall measures of tummy time exhibit an acceptable level of agreement with direct observation and can be reliably used over shorter periods. Parents of preterm infants may display a bias in recalling tummy time, leading to overestimations. To accurately assess tummy time in this population, a combination of subjective and objective measures should be explored. Plain-Language Summary: Tummy time is an essential movement experience for infants, especially for preterm infants, who are at a higher risk for motor delays. The most common way to track tummy time is through parent reports, or recall, versus a practitioner directly observing tummy time in the home. Despite the widespread use of parent recall to track tummy time, no study has examined the accuracy of parent recall versus direct observation in the home. Accurately assessing tummy time is crucial for improving and supporting health outcomes for infants. This study found that prematurity may affect the accuracy of parent recall for assessing tummy time in young infants. The authors discuss the implications of this finding and provide suggestions to guide the selection of appropriate methods to measure tummy time in clinical practice and research studies.

Agreement Analysis between Vive and Vicon Systems to Monitor Lumbar Postural Changes.

Immersive virtual reality has recently developed into a readily available system that allows for full-body tracking. Can this affordable system be used for component tracking to advance or replace expensive kinematic systems for motion analysis in the clinic? The aim of this study was to assess the accuracy of position and orientation measures from Vive wireless body trackers when compared to Vicon optoelectronic tracked markers attached to (1) a robot simulating trunk flexion and rotation by repeatedly moving to know locations, and (2) healthy adults playing virtual reality games necessitating significant trunk displacements. The comparison of both systems showed component tracking with Vive trackers is accurate within 0.68 ± 0.32 cm translationally and 1.64 ± 0.18° rotationally when compared with a three-dimensional motion capture system. No significant differences between Vive trackers and Vicon systems were found suggesting the Vive wireless sensors can be used to accurately track joint motion for clinical and research data.

Skill-Related Adaptive Modifications of Gaze Stabilization in Elite and Non-Elite Athletes.

The vestibular ocular reflex (VOR) provides gaze stability during head movements by driving eye movements in a direction opposing head motion. Although vestibular-based rehabilitation strategies are available, it is still unclear whether VOR can be modulated by training. By examining adaptations in gaze stabilization mechanisms in a population with distinct visuomotor requirements for task success (i.e., gymnasts), this study was designed to determine whether experience level (as a proxy of training potential) was associated with gaze stabilization modifications during fixed target (VOR promoting) and fixed-to-head-movement target (VOR suppressing) tasks. Thirteen gymnasts of different skill levels participated in VOR and VOR suppression tasks. The gain between head and eye movements was calculated and compared between skill levels using an analysis of covariance. Across experience levels, there was a similar degradation in VOR gain away from -1 at higher movement speeds. However, during the suppression tasks, more experienced participants were able to maintain VOR gain closer to 0 across movement speeds, whereas novice participants showed greater variability in task execution regardless of movement speed. Changes in adaptive modifications to gaze stability associated with experience level suggest that the mechanisms impacting gaze stabilization can be manipulated through training.

A Virtual Reality Game Suite for Graded Rehabilitation in Patients With Low Back Pain and a High Fear of Movement: Within-Subject Comparative Study.

BACKGROUND: Complex movement pathologies that are biopsychosocial in nature (eg, back pain) require a multidimensional approach for effective treatment. Virtual reality is a promising tool for rehabilitation, where therapeutic interventions can be gamified to promote and train specific movement behaviors while increasing enjoyment, engagement, and retention. We have previously created virtual reality-based tools to assess and promote lumbar excursion during reaching and functional gameplay tasks by manipulating the position of static and dynamic contact targets. Based on the framework of graded exposure rehabilitation, we have created a new virtual reality therapy aimed to alter movement speed while retaining the movement-promoting features of our other developments. OBJECTIVE: This study aims to compare lumbar flexion excursion and velocity across our previous and newly developed virtual reality tools in a healthy control cohort. METHODS: A total of 31 healthy participants (16 males, 15 females) took part in 3 gamified virtual reality therapies (ie, Reachality, Fishality, and Dodgeality), while whole-body 3D kinematics were collected at 100 Hz using a 14-camera motion capture system. Lumbar excursion, lumbar flexion velocity, and actual target impact location in the anterior and vertical direction were compared across each virtual reality task and between the 4 anthropometrically defined intended target impact locations using separate 2-way repeated measures analysis of variance models. RESULTS: There was an interaction between game and impact height for each outcome (all P<.001). Post-hoc simple effects models revealed that lumbar excursion was reduced during Reachality and Fishality relative to that during Dodgeality for the 2 higher impact heights but was greater during Reachality than during Fishality and Dodgeality for the lowest impact height. Peak lumbar flexion velocity was greater during Dodgeality than during Fishality and Reachality across heights. Actual target impact locations during Dodgeality and Fishality were lower relative to those during Reachality at higher intended impact locations but higher at lower intended impact locations. Finally, actual target impact location was further in the anterior direction for Reachality compared to that for Fishality and for Fishality relative to that for Dodgeality. CONCLUSIONS: Lumbar flexion velocity was reduced during Fishality relative to that during Dodgeality and resembled velocity demands more similar to those for a self-paced reaching task (ie, Reachality). Additionally, lumbar motion and target impact location during Fishality were more similar to those during Reachality than to those during Dodgeality, which suggests that this new virtual reality game is an effective tool for shaping movement. These findings are encouraging for future research aimed at developing an individualized and graded virtual reality intervention for patients with low back pain and a high fear of movement.

Botulinum toxin type A for nonsurgical lateral release in patellofemoral pain syndrome: a case study.

SETTING: Outpatient rehabilitation clinic. PATIENT: A 37-year-old physically active male. CASE DESCRIPTION: The patient presented with anterior left knee pain, exacerbated when climbing stairs, sitting, and running. Exam showed lateral tracking patellae and palpable crepitus. One hundred fifty units of botulinum toxin A was injected into his left vastus lateralis. He underwent a 12-week home exercise program targeting the vastus medialis (VM). ASSESSMENT/RESULTS: Visual analog scale decreased from 70 to 0 on a 150-mm scale, from initial until 8 weeks postinjection. Functional Index Questionnaire increased from 5 to 16 over the same period. Knee torque and surface electromyography findings showed increased activity of the VM during knee extension. CONCLUSION: Botulinum injection into the vastus lateralis in conjunction with VM strengthening may provide more effective treatment of patellofemoral pain syndrome. Further study is needed to explore this novel treatment of patellofemoral pain syndrome.

Distinguishing chronic low back pain in young adults with mild to moderate pain and disability using trunk compliance.

Chronic low back pain (cLBP) rates among younger individuals are rising. Although pain and disability are often less severe, underlying changes in trunk behavior may be responsible for recurrence. We examine the biomarker capacity of a simple Trunk Compliance Index (TCI) to distinguish individuals with and without cLBP. A random subset (n = 49) of the RELIEF RCT were matched to healthy controls for sex, age, height and weight. We measured TCI (as displacement/ weight-normalized perturbation force) using anthropometrically-matched, suddenly-applied pulling perturbations to the trunk segment, randomized across three planes of motion (antero-posterior, medio-lateral, and rotational). Mean differences between cLBP, sex and perturbation direction were assessed with repeated-measures analysis of variance. Discriminatory accuracy of TCI was assessed using Receiver Operator Characteristic (ROC) analysis. Baseline characteristics between groups were equivalent (x̅ [range]): sex (57% female / group), age (23.0 [18-45], 22.8 [18-45]), height, cm (173.0 [156.5-205], 171.3 [121.2-197], weight, kg (71.8 [44.5-116.6], 71.7 [46.8-117.5]) with cLBP associated with significantly lower TCI for 5 of 6 directions (range mean difference, - 5.35: - 1.49, range 95% CI [- 6.46: - 2.18 to - 4.35: - 0.30]. Classification via ROC showed that composite TCI had high discriminatory potential (area under curve [95% CI], 0.90 [0.84-0.96]), driven by TCI from antero-posterior perturbations (area under curve [95% CI], 0.99 [0.97-1.00]). Consistent reductions in TCI suggests global changes in trunk mechanics that may go undetected in classic clinical examination. Evaluation of TCI in younger adults with mild pain and disability may serve as a biomarker for chronicity, leading to improved preventative measures in cLBP.Trial Registration and Funding RELIEF is registered with clinicaltrials.gov (NCT01854892) and funded by the NIH National Center for Complementary & Integrative Health (R01AT006978).

The influence of gaze stabilization and fixation on stepping reactions in younger and older adults.

PURPOSE: To date, there has been little evidence to suggest the importance of foveal viewing versus peripheral retina viewing when trying to recover from a perturbation. The purposes of this investigation were to (1) determine whether a visual target can be stabilized on the fovea during a perturbation, (2) determine whether stepping responses following a perturbation are influenced by foveal fixation, and (3) compare gaze stability and stepping responses between young and aging adults. MATERIALS/METHODS: Ten young adults and 10 aging adults were asked to wear an eye-tracking device linked to a kinematic tracking system during perturbations. Perturbations were delivered under 2 conditions: control (no instructions regarding gaze location were given) and earth-fixed (EF) (subjects were asked to fixate gaze on an EF target). Stepping responses were recorded via force plates. Gaze stability, reported as percent foveal fixation (% FF), was calculated from eye-tracking data. Step latencies (SLs) were computed from force plate data. A 2 x 2 analysis of variance was used to assess statistical significance between groups. For the young and aging adults, linear correlations were made to identify relationships between % FF and SL. RESULTS: For each condition, aging adults took longer to initiate a step (control, P = .002; EF, P = .003). Young adults were better at maintaining gaze fixation than older adults (P = .0045). Linear correlations demonstrated significant negative relationships between SL and % FF for young (r = -0.76, P = .001) and older (r = -0.87, P = .0001) adults. As % FF increased, SL decreased. CONCLUSIONS: The ability to maintain gaze fixation of an EF target may be important in reducing SL following a perturbation. Older adult subjects demonstrated a decreased ability to fixate a target during balance tasks while also displaying longer SLs.

Isometric gluteus medius muscle torque and frontal plane pelvic motion during running.

The objective of this study was to investigate the relationship between isometric GM torque and the degree of frontal plane pelvic drop during running. Twenty-one healthy, recreational runners (9 males, 12 females) who ran 8.05 km or more per week were obtained from a sample of convenience. GM maximal isometric torque was collected prior to the run. Subjects then ran on a treadmill for 30 minutes while bilateral three-dimensional pelvic kinematic data were collected for 10 seconds at each 2 minute increment. Left side pelvic drop showed a slight increase (effect size = 0.61); while, the right side pelvic drop remained stable (effect size = 0.18). Pearson's Correlations showed no relationship between GM isometric torque and frontal plane pelvic drop for any of the data collection periods during the 30-minute run. These results suggest that isometric GM torque was a poor predictor of frontal plane pelvic drop. One should question whether a dynamic rather than static measure of GM strength would be more appropriate. Future research is needed to identify dynamic strength measures that would better predict biomechanical components of running gait. Key pointsThere is a lack of research linking static, clinical measures to dynamic running gait observations.Isometric gluteus medius muscle torque is a poor predictor of frontal plane pelvic drop in running.Future studies should identify dynamic strength measures that correlate with elements of running biomechanics.

A Motor Learning Paradigm Combining Technology and Associative Learning to Assess Prone Motor Learning in Infants.

BACKGROUND: Associative learning is the ability to discover a relationship between two or more events. We combined principles of learning and technology to develop a paradigm to assess associative learning in prone. PURPOSE: The purpose of this study was to determine whether 3- to 6-month-old infants can demonstrate: (1) short-term learning of an association between their upper body movements in prone and activation of a toy, and (2) retention of the association learned on day 1, 24 hours later. METHODS: Twenty-eight infants who were 3 to 6 months of age and who were typically developing were tested for 2 consecutive days in an instrumented play gym. Both days of testing had a baseline and 4 acquisition phases (2 minutes each). During the acquisition phase, the toy activated for a maximum of 10 seconds when the infant's head was above a threshold. A criterion was set a priori to distinguish infants as short-term learners and retainers of the association learned on day 1. RESULTS: Of 28 infants, 22 and 14 infants completed all phases of the testing on day 1 and day 2, respectively. Fourteen (50%) of the infants met the criteria for short-term learners. On day 2, there was an analyzable sample of 9 short-term learners. Three of the 12 short-term learners (25%) demonstrated retention on day 2. CONCLUSION: Consistent with prior infant motor learning research, half of the infants demonstrated associative learning in this novel assessment in prone; however, based on study criteria, the infants had limited retention of the association on day 2.

Rehabilitation of an elite gymnast with a type II manubriosternal dislocation.

BACKGROUND AND PURPOSE: This case report describes the rehabilitation of an elite, 15-year-old gymnast after a nonreduced type II manubriosternal dislocation. The rehabilitation took place in a gymnastics venue but was guided by a physician and a licensed physical therapist. CASE DESCRIPTION: The gymnast participated in a 13-week rehabilitation program for range of motion and strengthening that was based on a biomechanical hierarchy. Rehabilitation began at week 2 after injury for the lower extremities and at week 4 for the upper extremities. OUTCOMES: By week 4, the patient began upper-extremity strengthening, and by week 6, the patient had no pain with palpation and tolerated light sternal loading. At week 9, a plain-film radiograph revealed a stable manubriosternal joint, and by week 13, the patient returned to gymnastics pain-free. DISCUSSION: This case report shows that, after a 13-week regimen of progressive and repetitive, cyclical tensile and compressive loading, the manubriosternal joint was stable, and the elite gymnast was able to return to the sport, successfully competing in a regional competition.

Oculomotor tracking strategy in normal subjects with and without simulated scotoma.

PURPOSE: Experiments were conducted on five subjects with no visual impairment to assess tracking strategy differences in subjects with and without a simulated central scotoma. METHODS: Subjects were asked to visually track horizontally moving periodic and nonperiodic sinusoidal stimuli through a +/-5 degrees range. Scotoma simulation was achieved electronically with a closed-loop feedback system using horizontal eye movement measurements from a monocular limbus eye tracker updated at a rate of 500 Hz. The scotoma was centrally located and had defined horizontal half widths of 1, 2, and 3 degrees . Vertical eye position measurements from a video-based dark-pupil tracker were used to identify and remove trials in which extreme vertical eye position deviations reduced the effectiveness of the simulation. RESULTS: All subjects developed a preferred retinal locus (PRL) in the left visual field and demonstrated a tendency for saccadic redirection to this area. Saccadic endpoints into the PRL outnumbered foveally directed saccades by a factor of 2:1. The PRL was located outside the compromised central vision region, typically near the edge of the scotoma boundary, for all subjects except one. This subject had a PRL within the simulated scotoma under two conditions, but the percentage of total time spent at the "compromised" PRL was less than for other subjects. CONCLUSIONS: Subjects with no visual impairment confronted with a central scotoma develop a preferred retinal locus to replace the nonfunctional fovea and appear to suppress normal refoveating saccadic behavior in favor of this location.

Effects of Visual Display on Joint Excursions Used to Play Virtual Dodgeball.

BACKGROUND: Virtual reality (VR) interventions hold great potential for rehabilitation as commercial systems are becoming more affordable and can be easily applied to both clinical and home settings. OBJECTIVE: In this study, we sought to determine how differences in the VR display type can influence motor behavior, cognitive load, and participant engagement. METHODS: Movement patterns of 17 healthy young adults (8 female, 9 male) were examined during games of Virtual Dodgeball presented on a three-dimensional television (3DTV) and a head-mounted display (HMD). The participant's avatar was presented from a third-person perspective on a 3DTV and from a first-person perspective on an HMD. RESULTS: Examination of motor behavior revealed significantly greater excursions of the knee (P=.003), hip (P<.001), spine (P<.001), shoulder (P=.001), and elbow (P=.026) during HMD versus 3DTV gameplay, resulting in significant differences in forward (P=.003) and downward (P<.001) displacement of the whole-body center of mass. Analyses of cognitive load and engagement revealed that relative to 3DTV, participants indicated that HMD gameplay resulted in greater satisfaction with overall performance and was less frustrating (P<.001). There were no significant differences noted for mental demand. CONCLUSIONS: Differences in visual display type and participant perspective influence how participants perform in Virtual Dodgeball. Because VR use within rehabilitation settings is often designed to help restore movement following orthopedic or neurologic injury, these findings provide an important caveat regarding the need to consider the potential influence of presentation format and perspective on motor behavior.

Effects of Real-World Versus Virtual Environments on Joint Excursions in Full-Body Reaching Tasks.

Starting from an upright standing posture and reaching for a target that requires some forward bending of the trunk can involve many different configurations of the trunk and limb segments. We sought to determine if configurations of the limb and trunk segments during our standardized full-body reaching tasks were influenced by the visual environment. This paper examined movement patterns of healthy participants ([Formula: see text], eight female and nine male) performing full body reaching tasks to: 1) real-world targets; 2) virtual targets presented on a 3-D television; and 3) virtual targets presented using a head-mounted display. For reaches performed in the virtual world, the avatar was presented from a third-person perspective for the 3-D television and from a first-person perspective for the head-mounted display. Reaches to virtual targets resulted in significantly greater excursions of the ankle, knee, hip, spine, and shoulder compared with reaches made to real-world targets. This resulted in significant differences in the forward and downward displacements of the whole-body center of mass between the visual environments. Visual environment clearly influences how subjects perform full-body reaching tasks to static targets. Because a primary goal of virtual reality within rehabilitation is often to restore movement following orthopedic or neurologic injury, it is important to understand how visual environment will affect motor behavior. The present findings suggest that the existing game systems that track and present avatars from a third-person perspective elicit significantly different motor behavior when compared with the same tasks being presented from a first-person perspective.

Scapular muscle tests in subjects with shoulder pain and functional loss: reliability and construct validity.

BACKGROUND AND PURPOSE: Scapular muscle performance evaluated with a handheld dynamometer (HHD) has been investigated only in people without shoulder dysfunction for test-retest reliability of data obtained with a single scapular muscle test. The purpose of this study was to assess the reliability, error, and validity of data obtained with an HHD for 4 scapular muscle tests in subjects with shoulder pain and functional loss. SUBJECTS AND METHODS: Subjects (N=40) with shoulder pain and functional loss were tested by measuring the kilograms applied with an HHD during 3 trials for muscle tests for the lower trapezius, upper trapezius, middle trapezius, and serratus anterior muscles. Concurrently, surface electromyography (sEMG) data were collected for the 4 muscles. The same procedures were performed 24 to 72 hours after the initial testing by the same tester. Muscle tests were performed 3 times, and the results were averaged for data analysis. RESULTS: Intraclass correlation coefficients for intratester reliability of measurements of isometric force obtained using an HHD ranged from .89 to .96. The standard error of the measure (90% confidence interval [CI]) ranged from 1.3 to 2.7 kg; the minimal detectable change (90% CI) ranged from 1.8 to 3.6 kg. Construct validity assessment, done by comparing the amounts of isometric muscle activity (sEMG) for each muscle across the 4 muscle tests, revealed that the muscle activity of the upper trapezius and lower trapezius muscles was highest during their respective tests. Conversely, the isometric muscle activity of the middle trapezius and serratus anterior muscles was not highest during their respective tests. DISCUSSION AND CONCLUSION: In people with shoulder pain and functional loss, the intrarater reliability and error over 1 to 3 days were established using an HHD for measurement of isometric force for the assessment of scapular muscle performance. Error values can be used to make decisions regarding individual patients. Construct validity was established for the lower and upper trapezius muscle tests; therefore, these tests are advocated for use. However, construct validity was not demonstrated for the serratus anterior and middle trapezius muscle tests as performed in this study. Further investigation of these muscle tests is warranted.

Thoracic Spine Manipulation in Individuals With Subacromial Impingement Syndrome Does Not Immediately Alter Thoracic Spine Kinematics, Thoracic Excursion, or Scapular Kinematics: A Randomized Controlled Trial.

STUDY DESIGN: Randomized controlled trial. OBJECTIVES: To determine if thoracic spinal manipulative therapy (SMT) alters thoracic kinematics, thoracic excursion, and scapular kinematics compared to a sham SMT in individuals with subacromial impingement syndrome, and also to compare changes in patient-reported outcomes between treatment groups. BACKGROUND: Prior studies indicate that thoracic SMT can improve pain and disability in individuals with subacromial impingment syndrome. However, the mechanisms underlying these benefits are not well understood. METHODS: Participants with shoulder impingement symptoms (n = 52) were randomly assigned to receive a single session of thoracic SMT or sham SMT. Thoracic and scapular kinematics during active arm elevation and overall thoracic excursion were measured before and after the intervention. Patient-reported outcomes measured were pain (numeric pain-rating scale), function (Penn Shoulder Score), and global rating of change. RESULTS: Following the intervention, there were no significant differences in changes between groups for thoracic kinematics or excursion, scapular kinematics, and patient-reported outcomes (P>.05). Both groups showed an increase in scapular internal rotation during arm raising (mean, 0.9°; 95% confidence interval [CI]: 0.3°, 1.6°; P = .003) and lowering (0.8°; 95% CI: 0.0°, 1.5°; P = .041), as well as improved pain reported on the numeric pain-rating scale (1.2 points; 95% CI: 0.3, 1.8; P<.001) and function on the Penn Shoulder Score (9.1 points; 95% CI: 6.5, 11.7; P<.001). CONCLUSION: Thoracic spine extension and excursion did not change significantly following thoracic SMT. There were small but likely not clinically meaningful changes in scapular internal rotation in both groups. Patient-reported pain and function improved in both groups; however, there were no significant differences in the changes between the SMT and the sham SMT groups. Overall, patient-reported outcomes improved in both groups without meaningful changes to thoracic or scapular motion. LEVEL OF EVIDENCE: Therapy, level 1b-.

Immediate changes in pressure pain sensitivity after thoracic spinal manipulative therapy in patients with subacromial impingement syndrome: A randomized controlled study.

BACKGROUND: Thoracic SMT can improve symptoms in patients with subacromial impingement syndrome. However, at this time the mechanisms of SMT are not well established. It is possible that changes in pain sensitivity may occur following SMT. OBJECTIVES: To assess the immediate pain response in patients with shoulder pain following thoracic spinal manipulative therapy (SMT) using pressure pain threshold (PPT), and to assess the relationship of change in pain sensitivity to patient-rated outcomes of pain and function following treatment. DESIGN: Randomized Controlled Study. METHODS: Subjects with unilateral subacromial impingement syndrome (n = 45) were randomly assigned to receive treatment with thoracic SMT or sham thoracic SMT. PPT was measured at the painful shoulder (deltoid) and unaffected regions (contralateral deltoid and bilateral lower trapezius areas) immediately pre- and post-treatment. Patient-rated outcomes were pain (numeric pain rating scale - NPRS), function (Pennsylvania Shoulder Score - Penn), and global rating of change (GROC). RESULTS: There were no significant differences between groups in pre-to post-treatment changes in PPT (p ≥ 0.583) nor were there significant changes in PPT within either group (p ≥ 0.372) following treatment. NPRS, Penn and GROC improved across both groups (p < 0.001), but there were no differences between the groups (p ≥ 0.574). CONCLUSION: There were no differences in pressure pain sensitivity between participants receiving thoracic SMT versus sham thoracic SMT. Both groups had improved patient-rated pain and function within 24-48 h of treatment, but there was no difference in outcomes between the groups.

A muscle temperature compensation technique for EMG fatigue measures.

PURPOSE: The use of electromyogram-based fatigue measurements during high-intensity, dynamic activities is confounded by the accompanying increase in muscle temperature. The purpose of this communication was to demonstrate the use of a muscle temperature compensation technique for electromyogram (EMG) fatigue measurements. METHODS: Subjects were six healthy men (mean age 30.8 +/- 5.6 yr) with no recent history of lower extremity injury. In part 1 of this study, the relationship between muscle temperature and EMG mean power frequency was determined for the vastus lateralis muscle (VL). The VL was heated with diathermy to a temperature of approximately 39 degrees C. Isometric EMG data were collected during the performance of a nonfatiguing protocol as the muscle cooled (39-34 degrees C). In part 2 of this study, the subjects rode a lower-extremity ergometer at workloads of 25%, 50%, and 75% of their VO2max. Isometric EMG and intramuscular temperature data were collected from the VL during intermittent interruptions of the activity. The relationship between muscle temperature and EMG mean power frequency established in part 1 was used with the measured change in muscle temperature to correct for the effect of temperature on the EMG mean power frequency. RESULTS: The results from part 1 revealed a linear relationship between EMG mean power frequency and muscle temperature (N = 5, mean slope = 2.82 +/- 0.27 Hz. degrees C-1, R2 = 0.88 +/- 0.02). The mean slope was used as a muscle temperature compensation factor that quantified the influence of muscle temperature on EMG mean power frequency. For part 2, representative data from a single subject are presented to demonstrate the use of the muscle temperature compensation technique. CONCLUSION: A muscle temperature compensation technique for EMG mean power frequency analysis has been demonstrated. This technique corrects for the detrimental influence of muscle temperature changes on EMG fatigue measurements, thereby improving the efficacy of EMG fatigue measurements during high-intensity, dynamic activities that result in muscle temperature increases.

Changes in landing biomechanics during a fatiguing landing activity.

The objective of this study was to investigate the effects of LE fatigue on ground impact force, LE kinematics, and LE kinetics during landing. Ground reaction force (GRF), kinematic, and electromyogram (EMG) data were collected from 12 male subjects during a fatiguing landing activity (FLA). This activity allowed not only the biomechanical differences between unfatigued and fatigued landings to be determined, but also the time history of multiple biomechanical variables as fatigue progressed. EMG mean frequency analysis using data collected immediately before and after the FLA indicated that subjects experienced fatigue of the quadriceps muscles. Results indicated a decrease in ground impact force and an increase in maximum joint flexion during landing with fatigue. Joint impulse values were consistent with a distal to proximal redistribution of extensor moment production. Potential reasons for this redistribution are discussed. A trend reversal in hip and ankle impulse during the activity suggest a change in landing strategy as fatigue progressed. The data also suggest that the measured changes in landing biomechanics may have been influenced by other factors, in addition to fatigue, such as a neuromuscular protective mechanism to decrease impact force magnitude.

Adaptations in horizontal head stabilization in response to altered vision and gaze during natural walking.

The purpose of this study was to determine adaptations in head stability resulting from altered gaze control and vision during over-ground walking. Using over-ground walking permitted adaptations in walking velocity and cadence that are otherwise not possible during treadmill walking or walking-in-place. Gaze control and vision were manipulated by having 20 young adult subjects 1) walk naturally, 2) view a distant, earth-fixed target to enhance the vestibulo-ocular reflex (VOR), 3) view a head-fixed target to suppress the VOR, and 4) walk in darkness. Horizontal head and trunk angular velocities in space, walking velocity and cadence were measured. Root-mean-square head and trunk angular velocities were calculated and frequency analyses determined head-trunk movement patterns. Results demonstrated that when given the opportunity, subjects slowed down and decreased cadence in response to challenging tasks. Despite strongly reduced walking velocity and cadence, walking in darkness proved most challenging for head stabilization, indicating the importance of vision during this process. Viewing the earth-fixed target demonstrated the greatest head stability thereby, facilitating gaze stabilization. However, comparisons between the earth-fixed and head-fixed target conditions suggest a reciprocal relationship where gaze stability also facilitates head stability. This contribution of gaze stability to head stability is more important than vision alone as the head stabilization response was diminished during the VOR suppressed condition.