Comparison of multi-task ergonomic assessment methods for risk of upper extremity and low back musculoskeletal disorders.

Work-related musculoskeletal disorder of upper extremity multi-task assessment methods (Revised Strain Index [RSI], Distal Upper Extremity Tool [DUET]) and manual handling multi-task assessment methods (Revised NIOSH Lifting Equation [RNLE], Lifting Fatigue Failure Tool [LiFFT]) were compared. RSI and DUET showed a strong correlation (rs = 0.933, p < 0.001) where increasing risk factor exposure resulted in increasing outputs for both methods. RSI and DUET demonstrated fair agreement (κ = 0.299) in how the two methods classified outputs into risk categories (high, moderate or low) when assessing the same tasks. The RNLE and LiFFT showed a strong correlation (rs = 0.903, p = 0.001) where increasing risk factor exposure resulted in increasing outputs, and moderate agreement (κ = 0.574) in classifying the outputs into risk categories (high, moderate or low) when assessing the same tasks. The multi-task assessment methods provide consistent output magnitude rankings in terms of increasing exposure, however some differences exist between how different methods classify the outputs into risk categories.

The ACGIH TLV for lifting: Estimated TLVs for torso asymmetry beyond 30 degrees.

BACKGROUND: The American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) for Lifting is a manual material handling (MMH) assessment method to identify weight limits that nearly all workers may be exposed to without developing work-related low back disorders (LBD). However, this assessment method only applies to lifting with the torso within 30° asymmetry of the sagittal plane. OBJECTIVE: Estimate TLV weight limits while lifting with torso asymmetry greater than 30° beyond the sagittal plane. METHODS: Lifting tasks were performed from various horizontal and vertical locations, at torso asymmetry angles of 0°, 15°, 30°, 45°, 60°, 75° and 90°, using ACGIH identified TLVs. Validated MMH assessment methods (NIOSH Lifting Equation, Ohio State University LBD Risk Model) were utilized to estimate TLVs at torso asymmetries greater than 30°. RESULTS: The current ACGIH TLVs resulted in low- to moderate-risk risk levels for torso asymmetries from 0° to 30°, and the risk incrementally increased as torso asymmetry increased to 90°. With the intention to keep the risk levels to that found at 30° torso asymmetry, lower TLV weight limits in the vertical and horizontal zones investigated were estimated for torso asymmetries from 45° to 90°. The resulting adjusted TLVs were consistent with weight limits identified for similar lifting conditions from other assessment methods that account for torso asymmetry. CONCLUSIONS: This research found current ACGIH-defined TLVs possess less than high-risk for LBD, and provided guidance to practitioners for reduced TLVs when torso asymmetry is greater than 30° from the sagittal plane.

Influence of different passive shoulder exoskeletons on shoulder and torso muscle activation during simulated horizontal and vertical aircraft squeeze riveting tasks.

Aircraft manufacturing involves riveting utilizing squeeze riveting tools at heights from below elbow to overhead levels. This study assessed utilization of passive shoulder exoskeletons on shoulder and torso muscle activation during simulated squeeze riveting. Horizontal and vertical riveting tasks using squeeze riveting tools were performed by 16 aircraft workers wearing three different shoulder exoskeletons and a no-exoskeleton condition capturing electromyographic signals from shoulder and torso muscles. Exoskeletons reduced normalized EMG for the left anterior deltoid at both heights (6.6% and 15.7%), the right anterior deltoid (8.3%) and the right and left medial deltoid (9.3% and 8.9%) at the upper height for horizontal squeeze riveting. Exoskeletons reduced normalized EMG for the right and left anterior deltoids (7.0%-10.6%) and medial deltoids (1.3%-7.1%) within the upper zones during vertical squeeze riveting. Participants felt exoskeletons would be beneficial for squeeze riveting, however no preference was found among the exoskeletons used.

Torso Kinematics in Human Rolling Do Not Change When Upper Extremity Motion Is Constrained.

Human rolling, as turning in bed, is a fundamental activity of daily living. A quantitative analysis of rolling could help identify the neuromusculoskeletal disorders that prohibit rolling and develop interventions for individuals who cannot roll. This study sought to determine whether crossing the arms over the chest would alter fundamental coordination patterns when rolling. Kinematic data were collected from 24 subjects as they rolled with and without their arms crossed over their chest. Crossing the arms decreased the mean peak angular velocities of the shoulders (p = .001) and pelvis (p = .013) and influenced the mean duration of the roll (p = .057). There were no fundamental differences in shoulder and pelvis coordination when rolling with the arms crossed over the chest, implying that the arms may not have a major role in rolling.

The Reliability and Validity of Gluteal Endurance Measures (GEMs).

BACKGROUND: The gluteals have unique morphology related to muscle endurance, including moderate fiber sizes and a majority of Type I endurance fibers. Evidence suggests gluteal endurance is related to low back pain, running kinematics, balance, posture, and more. However, reliable and valid measures specific to gluteal endurance are lacking in the literature. HYPOTHESIS/PURPOSE: The purpose of this study was to examine the intra- and inter-rater reliability of two gluteal endurance measures (GEMs) for clinical use. It also aimed to examine validity for the two measures by using electromyography (EMG), recording reasons for task failure, and analyzing differences between demographic groups. STUDY DESIGN: Cross-Sectional. METHODS: Sixty-eight males and females with and without recurrent low back pain aged 18-35 years were recruited from a university population. Electromyography electrodes were placed on subjects' gluteus maximus and gluteus medius, and each subject performed three trials of GEM-A (abduction endurance) and GEM-B (bridging endurance). Hold times, EMG median frequency (MF) data, and subjective reasons for task failure were analyzed. RESULTS: Both GEMs demonstrated high intra-rater reliability (ICC = 0.87-0.94) and inter-rater reliability (ICC = 0.99). Mean hold times were 104.83 ± 34.11 seconds for GEM-A (abduction endurance) and 81.03 ± 24.79 seconds for GEM-B (bridging endurance). No statistically significant difference was found between subjects with and without recurrent LBP. Median frequency data validated the onset of gluteal fatigue during both measures. Posterolateral hip (gluteal) fatigue was reported as the primary reason for task failure in 93% and 86% of subjects for GEM-A and GEM-B, respectively. CONCLUSION: This seminal study of GEM-A (abduction endurance) and GEM-B (bridging endurance) found both measures to be reliable and valid measures of gluteal endurance. Further examination of the GEMs in samples with different types of LBP or hip pain is recommended. LEVEL OF EVIDENCE: 3.

Gluteal Muscle Activation During Common Yoga Poses.

BACKGROUND: Approximately 24% of physical therapists report regularly using yoga to strengthen major muscle groups. Although clinicians and athletes often use yoga as a form of strength training, little is known about the activation of specific muscle groups during yoga poses, including the gluteus maximus and medius. HYPOTHESIS/PURPOSE: The purpose of this study was to measure gluteus maximimus and gluteus medius activation via electromyography (EMG) during five common yoga poses. A secondary purpose of the current study was to examine differences in muscle activation between sexes and experience levels. STUDY DESIGN: Cross-Sectional. METHODS: Thirty-one healthy males and females aged 18-35 years were tested during five yoga poses performed in a randomized order. Surface EMG electrodes were placed on subjects' right gluteus maximus and gluteus medius. Subjects performed the poses on both sides following a maximal voluntary isometric contraction (MVIC) test for each muscle. All yoga pose EMG data were normalized to the corresponding muscle MVIC data. RESULTS: Highest gluteus maximus activation occurred during Half Moon Pose on the lifted/back leg (63.3% MVIC), followed by the stance/front leg during Half Moon Pose (61.7%), then the lifted/back leg during Warrior Three Pose (46.1%). Highest gluteus medius activation occurred during Half Moon Pose on the lifted/back leg (41.9%), followed by the lifted/back leg during the Warrior Three Pose (41.6%). A significant difference was found in %MVIC of gluteus medius activity between male and female subjects (p = 0.026), and between experienced and inexperienced subjects (p = 0.050), indicating higher activation among males and inexperienced subjects, respectively. CONCLUSION: Half Moon Pose and Warrior Three Pose elicited the highest activation for both the gluteus maximus and the gluteus medius. Higher gluteus medius activation was seen in males and inexperienced subjects compared to their female and experienced counterparts. LEVEL OF EVIDENCE: 3.

Simulation of Exoskeleton Alignment and its Effect on the Knee Extensor and Flexor Muscles.

This study presents the analysis of different knee joint impairments and their effects on the knee extensor and flexor muscles. Joint impairments can result from stroke, musculoskeletal diseases, or misalignment of an attached exoskeleton joint. Understanding the correlation between parameters involved in joint movement mechanisms as well as force interactions could provide insight to establish an appropriate design for exoskeletons. Joints can be powered or even be rectified in terms of alignment by exoskeletons to help a patient recover quickly. For the study, OpenSIM 4.0 was used to generate models and simulations of the human musculoskeletal structure with and without introduced knee joint impairments along the sagittal and transverse directions. A scenario to simulate the constraints of an exoskeleton designed with a single hinge joint to mimic the knee joint was also considered. Alterations to the knee joint axis within the range of +5.00 to -6.40 mm would result in a meaningful yet not a significant change in muscle stresses; the simulation outputs indicate that constraining the knee joint motion to the sagittal plane will only increase the force generated by the vastus lateralis muscle up to 4.3%.

The effects of a fatiguing lifting task on postural sway among males and females.

Lifting and falls comprise a large proportion of work related injuries. Repetitive lifting to the point of fatigue can affect postural sway, which is associated with fall risk. To investigate the effects of lifting and fatigue on postural sway in males and females, 35 participants (18 male, 17 female) were asked to lift a weighted box in sets of 25 lifts at 5 different incremental weights (10, 15, 20, 25, and 30 kg) until fatigue. Before and after each lifting set, participants performed a single leg balance test on a force platform to assess postural sway by means of center of pressure mean velocity. Analysis of pre-fatigue to post-fatigue postural sway measurements indicated that there were no significant differences in mean velocity when males and females were grouped together. However, when analyzed as separate groups, mean postural sway center of pressure velocity increased for males but did not for females, indicating that males and females use different strategies to maintain balance when fatigued.

BUILDING A BETTER GLUTEAL BRIDGE: ELECTROMYOGRAPHIC ANALYSIS OF HIP MUSCLE ACTIVITY DURING MODIFIED SINGLE-LEG BRIDGES.

BACKGROUND: Gluteal strength plays a role in injury prevention, normal gait patterns, eliminating pain, and enhancing athletic performance. Research shows high gluteal muscle activity during a single-leg bridge compared to other gluteal strengthening exercises; however, prior studies have primarily measured muscle activity with the active lower extremity starting in 90 ° of knee flexion with an extended contralateral knee. This standard position has caused reports of hamstring cramping, which may impede optimal gluteal strengthening. HYPOTHESIS/PURPOSE: The purpose of this study was to determine which modified position for the single-leg bridge is best for preferentially activating the gluteus maximus and medius. STUDY DESIGN: Cross-Sectional. METHODS: Twenty-eight healthy males and females aged 18-30 years were tested in five different, randomized single-leg bridge positions. Electromyography (EMG) electrodes were placed on subjects' gluteus maximus, gluteus medius, rectus femoris, and biceps femoris of their bridge leg (i.e., dominant or kicking leg), as well as the rectus femoris of their contralateral leg. Subjects performed a maximal voluntary isometric contraction (MVIC) for each tested muscle prior to performing five different bridge positions in randomized order. All bridge EMG data were normalized to the corresponding muscle MVIC data. RESULTS: A modified bridge position with the knee of the bridge leg flexed to 135 ° versus the traditional 90 ° of knee flexion demonstrated preferential activation of the gluteus maximus and gluteus medius compared to the traditional single-leg bridge. Hamstring activation significantly decreased (p < 0.05) when the dominant knee was flexed to 135 ° (23.49% MVIC) versus the traditional 90 ° (75.34% MVIC), while gluteal activation remained similarly high (51.01% and 57.81% MVIC in the traditional position, versus 47.35% and 57.23% MVIC in the modified position for the gluteus maximus and medius, respectively). CONCLUSION: Modifying the traditional single-leg bridge by flexing the active knee to 135 ° instead of 90 ° minimizes hamstring activity while maintaining high levels of gluteal activation, effectively building a bridge better suited for preferential gluteal activation. LEVEL OF EVIDENCE: 3.

Can the efficacy of electrically stimulated pedaling using a commercially available ergometer BE improved by minimizing the muscle stress-time integral?

INTRODUCTION: The cardiorespiratory and muscular strength benefits of functional electrical stimulation (FES) pedaling for spinal cord injury (SCI) subjects are limited because the endurance of electrically stimulated muscle is low. METHODS: We tested new electrical stimulation timing patterns (Stim3, designed using a forward dynamic simulation to minimize the muscle stress-time integral) to determine whether SCI subjects could increase work and metabolic responses when pedaling a commercial FES ergometer. Work, rate of oxygen uptake (VO(2)), and blood lactate data were taken from 11 subjects (injury level T4-T12) on repeated trials. RESULTS: Subjects performed 11% more work pedaling with Stim3 than with existing stimulation patterns (StimErg) (P = 0.043). Average (VO(2)) and blood lactate concentrations were not significantly different between Stim3 (442 ml/min, 5.9 mmol/L) and StimErg (417 ml/min, 5.9 mmol/L). CONCLUSION: The increased mechanical work performed with Stim3 supports the use of patterns that minimize the muscle stress-time integral to prolong FES pedaling.

Effects of fast functional electrical stimulation gait training on mechanical recovery in poststroke gait.

Stroke leads to gait impairments that can negatively influence quality of life. Functional electrical stimulation (FES) applied during fast walking (FastFES) is an effective gait rehabilitation strategy that can lead to improvements in gait performance, walking speed and endurance, balance, activity, and participation poststroke. The effect of FastFES gait training on mechanical energy utilization is not well understood. The objective of this study was to test the effects of 12 weeks of FastFES gait training on mechanical recovery indices of poststroke gait. Kinematic data were collected from 11 stroke survivors before and after 12 weeks of FastFES training. Mechanical recovery was calculated from the positive changes in vertical, anterior-posterior, and medial-lateral components of center of mass energy. The average mechanical recovery increased from 34.5% before training to 40.0% after training. The increase was statistically significant (P = 0.014). The average self-selected walking speed increased from 0.4 m/s to 0.7 m/s after the 12-week FastFES training. The results indicate that the subjects were better able to generate and utilize the external mechanical energy of walking after FastFES gait training. FastFES gait training has the capacity to increase the gait speed, improve the mechanical recovery, and reduce the mechanical energy expenditure of stroke survivors when they walk.

The effects of stimulating lower leg muscles on the mechanical work and metabolic response in functional electrically stimulated pedaling.

Functional electrical stimulation (FES) pedaling with the muscles of the upper leg has been shown to provide benefit to spinal cord injured (SCI) individuals. FES pedaling with electrical stimulation timing patterns that minimize the stress-time integral of activated muscles has been shown to increase the work individuals can perform during the exercise compared to existing FES stimulation timing patterns. Activation of the lower leg muscles could further enhance the benefit of FES pedaling by increasing the metabolic response to the exercise. For SCI individuals, the objectives of this study were to experimentally determine whether FES pedaling with the upper and lower leg muscles would affect the work generated and increase the physiological responses compared to pedaling with the upper leg muscles alone. Work, rate of oxygen consumption ·VO2, and blood lactate data were measured from nine SCI subjects (injury level T4-T12) as they pedaled using upper leg and upper and lower leg muscle groups on repeated trials. The subjects performed 6% more work with the upper and lower legs than with the upper legs alone, but the difference was not significant (p = 0.2433). The average rate of oxygen consumption associated with the upper leg muscles (441 ±231 mL/min) was not significantly different from the corresponding average for the upper and lower legs (473 ±213 mL/min) (p = 0.1176). The blood lactate concentration associated with the upper leg muscles (5.9 ±2.3 mmoles/L) was significantly lower than the corresponding average for the upper and lower legs (6.8 ±2.3 mmoles/L) (p = 0.0049). The results indicate that electrical stimulation timing patterns that incorporate the lower leg muscles do increase the blood lactate concentrations. However, there was not enough evidence to reject the null hypothesis that stimulating the lower leg muscles affected the work accomplished or increased the rate of oxygen consumption. In conclusion, incorporating the lower leg muscles in the exercise does not lead to negative effects and could result in enhanced exercise outcomes in the long term.

Muscle stimulation waveform timing patterns for upper and lower leg muscle groups to increase muscular endurance in functional electrical stimulation pedaling using a forward dynamic model.

Functional electrical stimulation (FES) of pedaling provides a means by which individuals with spinal cord injury can obtain cardiorespiratory exercise. However, the early onset of muscle fatigue is a limiting factor in the cardiorespiratory exercise obtained while pedaling an FES ergometer. One objective of this study was to determine muscle excitation timing patterns to increase muscle endurance in FES pedaling for three upper leg muscle groups and to compare these timing patterns to those used in a commercially available FES ergometer. The second objective was to determine excitation timing patterns for a lower leg muscle group in conjunction with the three upper leg muscle groups. The final objective was to determine the mechanical energy contributions of each of the muscle groups to drive the crank. To fulfill these objectives, we developed a forward dynamic simulation of FES pedaling to determine electrical stimulation on and off times that minimize the muscle stress-time integral of the stimulated muscles. The computed electrical stimulation on and off times differed from those utilized by a commercially available FES ergometer and resulted in 17% and 11% decrease in the muscle stress-time integral for the three upper leg muscle groups and four upper and lower leg muscle groups, respectively. Also, the duration of muscle activation by the hamstrings increased by 5% over a crank cycle for the computed stimulation on and off times, and the mechanical energy generated by the hamstrings increased by 20%. The lower leg muscle group did not generate sufficient mechanical energy to reduce the energy contributions of the upper leg muscle groups. The computed stimulation on and off times could prolong FES pedaling, and thereby provide improved cardiorespiratory and muscle training outcomes for individuals with spinal cord injury. Including the lower leg muscle group in FES pedaling could increase cardiorespiratory demand while not affecting the endurance of the muscles involved in the pedaling task.

Influence of pedaling rate on muscle mechanical energy in low power recumbent pedaling using forward dynamic simulations.

An understanding of the muscle power contributions to the crank and limb segments in recumbent pedaling would be useful in the development of rehabilitative pedaling exercises. The objectives of this work were to 1) quantify the power contributions of the muscles to driving the crank and limb segments using a forward dynamic simulation of low-power pedaling in the recumbent position, and 2) determine whether there were differences in the muscle power contributions at three different pedaling rates. A forward dynamic model was used to determine the individual muscle excitation amplitude and timing to drive simulations that best replicated experimental kinematics and kinetics of recumbent pedaling. The segment kinematics, pedal reaction forces, and electromyograms (EMG) of 10 muscles of the right leg were recorded from 16 subjects as they pedaled a recumbent ergometer at 40, 50, and 60 rpm and a constant 50 W workrate. Intersegmental joint moments were computed using inverse dynamics and the muscle excitation onset and offset timing were determined from the EMG data. All quantities were averaged across ten cycles for each subject and averaged across subjects. The model-generated kinematic and kinetic quantities tracked almost always within 1 standard deviation (SD) of the experimental data for all three pedaling rates. The uniarticular hip and knee extensors generated 65% of the total mechanical work in recumbent pedaling. The triceps surae muscles transferred power from the limb segments to the crank and the bi-articular muscles that crossed the hip and knee delivered power to the crank during the leg transitions between flexion and extension. The functions of the individual muscles did not change with pedaling rate, but the mechanical energy generated by the knee extensors and hip flexors decreased as pedaling rate increased. By varying the pedaling rate, it is possible to manipulate the individual muscle power contributions to the crank and limb segments in recumbent pedaling and thereby design rehabilitative pedaling exercises to meet specific objectives.

How changing the inversion/eversion foot angle affects the nondriving intersegmental knee moments and the relative activation of the vastii muscles in cycling.

Nondriving intersegmental knee moment components (i.e., varus/valgus and internal/external axial moments) are thought to be primarily responsible for the etiology of overuse knee injuries such as patellofermoral pain syndrome in cycling because of their relationship to muscular imbalances. However the relationship between these moments and muscle activity has not been studied. Thus the four primary objectives of this study were to test whether manipulating the inversion/eversion foot angle alters the varus/valgus knee moment (Objective 1) and axial knee moment (Objective 2) and to determine whether activation patterns of the vastus medialis oblique (VMO), vastus lateralis (VL), and tensor fascia latae (TFL) were affected by changes in the varus/valgus (Objective 3) and axial knee moments (Objective 4). To fulfill these objectives, pedal loads and lower limb kinematic data were collected from 15 subjects who pedaled with five randomly assigned inversion/eversion angles: 10 deg and 5 deg everted and inverted and 0 deg (neutral). A previously described mathematical model was used to compute the nondriving intersegmental knee moments throughout the crank cycle. The excitations of the VMO, VL, and TFL muscles were measured with surface electromyography and the muscle activations were computed. On average, the 10-deg everted position decreased the peak varus moment by 55% and decreased the peak internal axial moment by 53% during the power stroke (crank cycle region where the knee moment is extensor). A correlation analysis revealed that the VMO/VL activation ratio increased significantly and the TFL activation decreased significantly as the varus moment decreased. For both the VMO/VL activation ratio and the TFL activation, a path analysis indicated that the varus/valgus moment was highly correlated to the axial moment but that the correlation between muscle activation and the varus moment was due primarily to the varus/valgus knee moment rather than the axial knee moment. The conclusion from these results is that everting the foot may be beneficial towards either preventing or ameliorating patellofemoral pain syndrome in cycling.

Functional roles of the leg muscles when pedaling in the recumbent versus the upright position.

An understanding of the coordination of the leg muscles in recumbent pedaling would be useful to the design of rehabilitative pedaling exercises. The objectives of this work were to (i) determine whether patterns of muscle activity while pedaling in the recumbent and upright positions are similar when the different orientation in the gravity field is considered, (ii) compare the functional roles of the leg muscles while pedaling in the recumbent position to the upright position to the upright position and (iii) determine whether leg muscle onset and offset timing for recumbent and upright pedaling respond similarly to changes in pedaling rate. To fulfill these objectives, surface electromyograms were recorded from 10 muscles of 15 subjects who pedaled in both the recumbent and upright positions at 75, 90, and 105 rpm and at a constant workrate of 250 W. Patterns of muscle activation were compared over the crank cycle. Functional roles of muscles in recumbent and upright pedaling were compared using the percent of integrated activation in crank cycle regions determined previously for upright pedaling. Muscle onset and offset timing were also compared. When the crank cycle was adjusted for orientation in the gravity field, the activation patterns for the two positions were similar. Functional roles of the muscles in the two positions were similar as well. In recumbent pedaling, the uniarticular hip and knee extensors functioned primarily to produce power during the extension region of the crank cycle, whereas the biarticular muscles crossing the hip and knee functioned to propel the leg through the transition regions of the crank cycle. The adaptations of the muscles to changes in pedaling rate were also similar for the two body positions with the uniarticular power producing muscles of the hip and knee advancing their activity to earlier in the crank cycle as the pedaling rate increased. This information on the functional roles of the leg muscles provides a basis by which to form functional groups, such as power-producing muscles and transition muscles, to aid in the development of rehabilitative pedaling exercises and recumbent pedaling simulations to further our understanding of task-dependent muscle coordination.