Khoirul Muslim

Disturbance and recovery of trunk stiffness and reflexive muscle responses following prolonged trunk flexion: influences of flexion angle and duration.

BACKGROUND Experimental studies suggest that flexed working postures reduce passive support of the spine, which could represent a significant risk factor for the development of occupational low back disorders. Neuromuscular compensations to reduced passive stiffness include increases in baseline activity or reflexive activation of trunk muscles. Yet, alterations and recovery of the synergy between active and passive tissues following prolonged flexion in humans are currently unknown. METHODS Twelve healthy participants were exposed to all combinations of two trunk flexion durations (2 and 16 min) and three flexion angles (33, 66, and 100% of individual flexion-relaxation angle). Load relaxation was recorded throughout exposures, whereas trunk stiffness and reflexive behaviors of the lumbar extensor muscles were investigated during dynamic responses to sudden perturbations. FINDINGS The magnitude of load relaxation increased with increasing flexion angle. Trunk stiffness decreased and reflex gains increased following flexion exposures; for both outcomes, acute changes were larger following exposure to increasing flexion angle. Reflex gains remained elevated one hour after exposure to maximum flexion. INTERPRETATION Exposure to prolonged trunk flexion changed trunk stiffness and reflex behavior in patterns consistent with epidemiological evidence linking such exposure with the risk of occupational low back disorders. Observed increases in reflex gains, at least among healthy individuals, may be a compensation for decreases in passive trunk stiffness following acute exposure to flexed postures. It remains to be determined whether the neuromuscular system can similarly respond to accumulated disturbances in passive structures following exposure to repeated flexion tasks.

Disturbance and recovery of trunk mechanical and neuromuscular behaviours following prolonged trunk flexion: influences of duration and external load on creep-induced effects

Trunk flexion results in adverse mechanical effects on the spine and is associated with a higher incidence of low back pain. To examine the effects of creep deformation on trunk behaviours, participants were exposed to full trunk flexion in several combinations of exposure duration and external load. Trunk mechanical and neuromuscular behaviours were obtained pre- and post-exposure and during recovery using sudden perturbations. Intrinsic trunk stiffness decreased with increasing flexion duration and in the presence of the external load. Recovery of intrinsic stiffness required more time than the exposure duration and was influenced by exposure duration. Reflexive trunk responses increased immediately following exposure but recovered quickly (∼2.5 min). Alterations in reflexive trunk behaviour following creep deformation exposures may not provide adequate compensation to allow for complete recovery of concurrent reductions in intrinsic stiffness, which may increase the risk of injury due to spinal instability. Statement of relevance: An increased risk of low back injury may result from flexion-induced disturbances to trunk behaviours. Such effects, however, appear to depend on the type of flexion exposure, and have implications for the design of work involving trunk flexion.

Disturbance and recovery of trunk mechanical and neuromuscular behaviours following repetitive lifting: influences of flexion angle and lift rate on creep-induced effects

Repetitive lifting is associated with an increased risk of occupational low back disorders, yet potential adverse effects of such exposure on trunk mechanical and neuromuscular behaviours were not well described. Here, 12 participants, gender balanced, completed 40 min of repetitive lifting in all combinations of three flexion angles (33, 66, and 100% of each participants full flexion angle) and two lift rates (2 and 4 lifts/min). Trunk behaviours were obtained pre- and post-exposure and during recovery using sudden perturbations. Intrinsic trunk stiffness and reflexive responses were compromised after lifting exposures, with larger decreases in stiffness and reflexive force caused by larger flexion angles, which also delayed reflexive responses.Consistent effects of lift rate were not found. Except for reflex delay no measures returned to pre-exposure values after 20 min of recovery. Simultaneous changes in both trunk stiffness and neuromuscular behaviours may impose an increased risk of trunk instability and low back injury. Practitioner summary An elevated risk of low back disorders is attributed to repetitive lifting. Here, the effects of flexion angle and lift rate on trunk mechanical and neuromuscular behaviours were investigated. Increasing flexion angle had adverse effects on these outcomes, although lift rate had inconsistent effects and recovery time was more than 20 min.

Evidence for an exposure-response relationship between trunk flexion and impairments in trunk postural control

Prolonged trunk flexion alters passive and active trunk tissue behaviors, and exposure-response relationships between the magnitude of trunk flexion exposure and changes in these behaviors have been reported. This study assessed whether similar exposure-response relationships exist between such exposures and impairments in trunk postural control. Twelve participants (6 M, 6 F) were exposed to three distinct trunk flexion conditions (and a no-flexion control condition), involving different flexion durations with/without an external load, and which induced differing levels of passive tissue creep. Trunk postural control was assessed prior to and immediately following trunk flexion exposures, and during 10 min of standing recovery, by tracking center of pressure (COP) movements during a seated balance task. All COP-based sway measures increased following each flexion exposure. In the anteroposterior direction, these increases were larger with increasing exposure magnitude, whereas such a relationship was not evident for mediolateral sway measures. All measures were fully recovered following 10 min of standing. The present results provide evidence for an exposure-response relationship between trunk flexion exposures and impairments in trunk postural control; specifically, larger impairments following increased exposures (i.e., longer flexion duration and presence of external load). Such impairments in trunk postural control may result from some combination of reduced passive trunk stiffness and altered/delayed trunk reflex responses, and are generally consistent with prior evidence of exposure-dependent alterations in trunk mechanical and neuromuscular behaviors assessed using positional trunk perturbations. Such evidence suggests potential mechanistic pathways through which trunk flexion exposures may contribute to low-back injury risk.

Traditional posterior load carriage: effects of load mass and size on torso kinematics, kinetics, muscle activity and movement stability.

Traditional posterior load carriage (PLC), done without the use of an assistive device (e.g. backpack), has been associated with low back pain (LBP) development. This study evaluated the effects of important task demands, related to load mass and size, on potential mechanisms linking traditional PLC with LBP. Nine healthy participants completed PLC tasks with three load masses (20%, 35% and 50% of individual body mass) and three load sizes (small, medium and large). Torso kinematics, kinetics, muscle activity and slip risk were evaluated during PLC on a walkway, and torso movement stability was quantified during PLC on a treadmill. Increasing load mass caused increased torso flexion, L5/S1 flexion moment, abdominal muscle activity and torso movement stability in the frontal plane. Increasing load size also caused higher torso flexion, peak torso angular velocity and acceleration, and abdominal muscle activity. Complex interactive effects of load mass and size were found on paraspinal muscle activity and slip risk. Specific task demands, related to load mass and size, may thus influence the risk of LBP during PLC. Practitioner Summary: This study examined the effects of load mass and size on low back pain (LBP) risk using intermediary measures derived from torso kinematics, kinetics and muscle activity. Our current findings, along with earlier work, suggest that load mass and size can influence LBP risk, and that use of smaller and light loads may be beneficial during PLC.

Musculoskeletal symptoms associated with posterior load carriage: An assessment of manual material handling workers in Indonesia

BACKGROUND Concerns have been raised regarding the high prevalence of musculoskeletal symptoms (MSS) among manual material handling (MMH) workers. However, limited investigations have been undertaken among one large group of workers using a particular MMH method called posterior load carriage (PLC). This is typically done without the use of a backpack in developing countries, and involves exposure to known risk factors for MSS such as heavy loads, non-neutral postures, and high levels of repetition. OBJECTIVES To 1) determine the types and prevalence of MSS among PLC workers and the impacts of these MSS on workers, 2) explore job demands potentially contributing to MSS, and (3) obtain input from workers regarding possible improvements to facilitate future interventions. METHODS Structured interview applied to 108 workers to assess PLC worker characteristics and job demands in eight cities in Indonesia. RESULTS MSS were reported in all anatomical regions evaluated, with symptoms most commonly reported at the lower back (72.2%), feet (69.4%), knees (64%), shoulders (47.2%), and neck (41.7%). Logistic regression indicated that MSS in the lower back were associated with longer work hours/day, MSS in the hands were associated with load mass, and MSS in the ankles/feet were associated with stature and load carriage frequency. MSS were reported to interfere with daily activity, but only few workers sought medical treatment. Possible improvements included the use of a belt, hook, or backpack/frame, and changes in the carriage method. CONCLUSIONS The study suggests that PLC workers incur a relatively high MSS burden. Future studies are needed to develop and evaluate practical interventions and specific guidelines to improve working conditions and occupational health and safety for PLC workers.

The sensitivity of galvanic skin response for assessing mental workload in indonesia.

BACKGROUND Objective measures have been shown to be equally sensitive in different cultures. However, these measures need special devices that are relatively expensive and need expertise to analyze the result. In Indonesia, there is a need for a sensitive and affordable mental workload measure. OBJECTIVE To evaluate the sensitivity of Galvanic Skin Response (GSR) in assessing mental workload in Indonesia. PARTICIPANTS A total of 72 Indonesian students with normal visual capability. METHOD Participants were asked to work on visual memory search task with a secondary task of counting with three different levels of difficulty. GSR, Heart Rate Variability (HRV), and the NASA-TLX were administered prior to, during, and after the tasks. RESULTS GSR measure was compared to NASA-TLX and HRV measures. Like the HRV, GSR showed to be sensitive in distinguishing rest and task condition significantly but not sensitive in distinguishing different levels of mental workload. In contrast, both the NASA-TLX and performance measure were sensitive in differentiating different levels of mental workload. CONCLUSIONS GSR has potential as a simple, cost-effective tool for measuring mental workload in Indonesia.

The effects of a simple intervention on exposures to low back pain risk factors during traditional posterior load carriage

Traditional posterior load carriage (PLC), typically performed without the use of an assistive device, is associated with a high prevalence of low back pain (LBP). However, there are few studies that have evaluated potential interventions to reduce exposures to LBP risk factors. This work examined the effects of a simple, potentially low-cost intervention using an assistive device (i.e., carrying aid) on exposures to factors related to LBP risk during PLC. Torso kinematics and kinetics, slip risk, and ratings of perceived discomfort (RPD) were obtained during simulated PLC on a walkway. Consistent with earlier results, increasing load mass substantially increased torso flexion and lumbosacral flexion moment, as well as RPDs in all anatomical regions evaluated. Using the carrying aid with a higher load placement resulted in substantially lower mean lumbosacral moments when carrying the heaviest load. In contrast, using the carrying aid with a lower load placement resulted in substantially higher torso flexion angles, higher mean lumbosacral moments when carrying heavier loads, and higher peak lumbosacral moments across all load masses. With use of the carrying aid, both higher and lower load placement resulted in significantly lower RPDs in the elbows and hands compared to the control condition. In summary, use of a carrying aid with higher load placement may be beneficial in reducing the risk of LBP during PLC. Future studies are needed, though, to improve the device design and to enhance external validity.