Influences of backpack loading on recovery from anterior and posterior losses of balance: An exploratory investigation.

Backpacks are common devices for carrying external posterior loads. However, relatively little is known about how these external loads affect the ability to recover from balance loss. In this exploratory investigation, 16 young adults (8 female, 8 male) performed forward and backward lean-and-release balance recovery trials, while wearing a backpack that was unloaded or loaded (at 15% of individual body weight). We quantified the effects of backpack loading on balance recovery in terms of maximum recoverable lean angles, center-of-mass kinematics, and temporal-spatial stepping characteristics. Mean values of maximum lean angles were 20° and 9° in response to forward and backward perturbations, respectively. These angles significantly decreased when wearing the additional load for only backward losses of balance. During backward losses of balance, the additional load decreased peak center-of-mass velocity and increased acceleration by ∼10 and 18% respectively, which was accompanied by ∼5% faster stepping responses and steps that were ∼9% longer, 11% higher, and had an ∼10% earlier onset. Thus, wearing a backpack decreases backward balance recovery ability and changes backward recovery stepping characteristics.

The Effect of Wave Motion Intensities on Performance in a Simulated Search and Rescue Task and the Concurrent Demands of Maintaining Balance.

OBJECTIVE: The purpose of this study was to examine how intensity of wave motions affects the performance of a simulated maritime search and rescue (SAR) task. BACKGROUND: Maritime SAR is a critical maritime occupation; however, the effect of wave motion intensity on worker performance is unknown. METHODS: Twenty-four participants (12 male, 12 female) performed a simulated search and rescue task on a six-degree-of-freedom motion platform in two conditions that differed in motion intensity (low and high). Task performance, electromyography (EMG), and number of compensatory steps taken by the individual were examined. RESULTS: As magnitude of simulated motion increased, performance in the SAR task decreased, and was accompanied by increases in lower limb muscle activation and number of steps taken. CONCLUSIONS: Performance of an SAR task and balance control may be impeded by high-magnitude vessel motions. APPLICATION: This research has the potential to be used by maritime engineers, occupational health and safety professionals, and ergonomists to improve worker safety and performance for SAR operators.

Quantifying Segmental Contributions to Center-of-Mass Motion During Dynamic Continuous Support Surface Perturbations Using Simplified Estimation Models.

Investigating balance reactions following continuous, multidirectional, support surface perturbations is essential for improving our understanding of balance control in moving environments. Segmental motions are often incorporated into rapid balance reactions following external perturbations to balance, although the effects of these motions during complex, continuous perturbations have not been assessed. This study aimed to quantify the contributions of body segments (ie, trunk, head, upper extremity, and lower extremity) to the control of center-of-mass (COM) movement during continuous, multidirectional, support surface perturbations. Three-dimensional, whole-body kinematics were captured while 10 participants experienced 5 minutes of perturbations. Anteroposterior, mediolateral, and vertical COM position and velocity were calculated using a full-body model and 7 models with reduced numbers of segments, which were compared with the full-body model. With removal of body segments, errors relative to the full-body model increased, while relationship strength decreased. The inclusion of body segments appeared to affect COM measures, particularly COM velocity. Findings suggest that the body segments may provide a means of improving the control of COM motion, primarily its velocity, during continuous, multidirectional perturbations, and constitute a step toward improving our understanding of how the limbs contribute to balance control in moving environments.

Energy cost associated with moving platforms.

BACKGROUND: Previous research suggests motion induced fatigue contributes to significant performance degradation and is likely related to a higher incidence of accidents and injuries. However, the exact effect of continuous multidirectional platform perturbations on energy cost (EC) with experienced personnel on boats and other seafaring vessels remains unknown. OBJECTIVE: The objective of this experiment was to measure the metabolic ECs associated with maintaining postural stability in a motion-rich environment. METHODS: Twenty volunteer participants, who were free of any musculoskeletal or balance disorders, performed three tasks while immersed in a moving environment that varied motion profiles similar to those experienced by workers on a mid-size commercial fishing vessel (static platform (baseline), low and high motions (HMs)). Cardiorespiratory parameters were collected using an indirect calorimetric system that continuously measured breath-by-breath samples. Heart rate was recoded using a wireless heart monitor. RESULTS: Results indicate a systematic increase in metabolic costs associated with increased platform motions. The increases were most pronounced during the standing and lifting activities and were 50% greater during the HM condition when compared to no motion. Increased heart rates were also observed. DISCUSSION: Platform motions have a significant impact on metabolic costs that are both task and magnitude of motion dependent. Practitioners must take into consideration the influence of motion-rich environments upon the systematic accumulation of operator fatigue.

The effects of short-term and long-term experiences on co-contraction of lower extremity postural control muscles during continuous, multi-directional support-surface perturbations.

While reactive balance control in response to single perturbations in quiet standing is relatively well understood, some occupational environments (e.g. maritime environments) expose workers to continuous, multi-directional challenges to balance and postural control, which require workers to respond to the current perturbation, as well as anticipate coming perturbations. Investigation of muscle activation patterns during continuous, multi-directional perturbations, and the role of previous experience, is warranted to better understand postural control strategies in these types of environments. This study aimed to identify changes in co-contraction in the lower extremity postural control muscles during multi-directional support-surface perturbations as a result of short-term and long-term experience. Twenty-five participants (12 with minimal experience (novice), 13 with ≥6 months experience working in moving maritime environments (experienced)) were exposed to five 5-minute trials of continuous support-surface perturbations. Muscle activity was recorded from six muscles bilaterally. Co-contraction indices were calculated for selected muscle pairings and compared between groups and trials. Co-contraction decreased across trials, and was lower in the experienced group relative to the novice group. These findings provide insight into the influence of previous experience on muscle activation during reactive balance control, and suggest that increased co-contraction may be a potential mechanism of the increased risk of workplace fatigue, falls, and injury in novice maritime workers. The development and refinement of training programs targeting novice workers may be a potential avenue to reduce fall and injury risk in maritime environments.

Population Differences in Postural Response Strategy Associated with Exposure to a Novel Continuous Perturbation Stimuli: Would Dancers Have Better Balance on a Boat?

Central or postural set theory suggests that the central nervous system uses short term, trial to trial adaptation associated with repeated exposure to a perturbation in order to improve postural responses and stability. It is not known if longer-term prior experiences requiring challenging balance control carryover as long-term adaptations that influence ability to react in response to novel stimuli. The purpose of this study was to determine if individuals who had long-term exposure to balance instability, such as those who train on specific skills that demand balance control, will have improved ability to adapt to complex continuous multidirectional perturbations. Healthy adults from three groups: 1) experienced maritime workers (n = 14), 2) novice individuals with no experience working in maritime environments (n = 12) and 3) individuals with training in dance (n = 13) participated in the study. All participants performed a stationary standing task while being exposed to five 6 degree of freedom motions designed to mimic the motions of a ship at sea. The balance reactions (change-in-support (CS) event occurrences and characteristics) were compared between groups. Results indicate dancers demonstrated significantly fewer CS events than novices during the first trial, but did not perform as well as those with offshore experience. Linear trend analyses revealed that short-term adaptation across all five trials was dependent on the nature of participant experience, with dancers achieving postural stability earlier than novices, but later than those with offshore experience. These results suggest that long term previous experiences also have a significant influence on the neural control of posture and balance in the development of compensatory responses.

The effects of moving environments on thoracolumbar kinematics and foot center of pressure when performing lifting and lowering tasks.

The purpose of this study was to examine how wave-induced platform motion effects postural stability when handling loads. Twelve participants (9 male, 3 female) performed a sagittal lifting/lowering task with a 10 kg load in different sea conditions off the coast of Halifax, Nova Scotia, Canada. Trunk kinematics and foot center of force were measured using the Lumbar Motion Monitor and F-Scan foot pressure system respectively. During motion conditions, significant decreases in trunk velocities were accompanied by significant increases in individual foot center of pressure velocities. These results suggest that during lifting and lowering loads in moving environments, the reaction to the wave-induced postural disturbance is accompanied by a decrease in performance speed so that the task can be performed more cautiously to optimize stability.

A survey of musculoskeletal injuries amongst Canadian massage therapists.

A survey was administered to registered massage therapists (RMT) across Canada to determine the prevalence of musculoskeletal pain and discomfort to the low back, shoulders, neck, wrist and thumbs associated with therapeutic treatments. A total of 502 RMT responded to the survey. Despite the majority of the respondents indicating they received proper training in therapy postures and self-care, there was a high prevalence of pain reporting to all areas of the upper extremity. The highest reporting of pain and discomfort was reported in the wrist and thumb, followed by the low back, neck and shoulders, respectively. There were no significant gender differences in pain/discomfort reporting except for the neck. The results of this survey indicate a high prevalence of musculoskeletal pain and discomfort associated with delivering massage therapy treatments. Therapists must focus on proper technique posture and adhere to a regime of self-care to reduce the risks of pain and injury. Further research is needed to determine the effects of neuromuscular fatigue and technique accommodation as it relates to pain risk.