The influence of age on spinal and lower limb muscle activity during repetitive lifting.

This study investigated the effects of age on upper erector spinae (UES), lower erector spinae (LES) and lower body (gluteus maximus; biceps femoris; and vastus lateralis) muscle activity during a repetitive lifting task. Twenty-four participants were assigned to two age groups: 'younger' (n = 12; mean age ± SD = 24.6 ± 3.6 yrs) and 'older' (n = 12; mean age = 46.5 ± 3.0 yrs). Participants lifted and lowered a box (13 kg) repetitively at a frequency of 10 lifts per minute for a maximum of 20 min. EMG signals were collected every minute and normalised to a maximum voluntary isometric contraction. A submaximal endurance test of UES and LES was used to assess fatigue. Older participants showed higher levels of UES and LES muscle activity (approximately 12-13%) throughout the task, but less fatigue compared to the younger group post-task completion. When lifting, lower-limb muscle activity was generally higher in older adults, although temporal changes were similar. While increased paraspinal muscle activity may increase the risk of back injury in older workers when repetitive lifting, younger workers may be more susceptible to fatigue-related effects. Education and training in manual materials handling should consider age-related differences when developing training programmes.

Age-related differences do affect postural kinematics and joint kinetics during repetitive lifting.

BACKGROUND: Age is considered a risk factor for manual handling-related injuries and older workers incur higher injury-related costs than younger co-workers. This study investigated the differences between the kinematics and kinetics of repetitive lifting in two groups of handlers of different ages. METHODS: Fourteen younger (mean 24.4 yr) and 14 older (mean 47.2 yr) males participated in the study. Participants repetitively lifted a box weighing 13 kg at a frequency of 10 lifts/min for a maximum of 20 min. Postural kinematics (joint and lumbosacral angles and angular velocities) and kinetics (joint moments) were measured throughout the lifting task using motion analysis and ground reaction forces. Muscle fatigue of the erector spinae was assessed using electromyography. FINDINGS: Peak lumbosacral, trunk, hip and knee flexion angles differed significantly between age groups over the duration of the task, as did lumbosacral and trunk angular velocities. The younger group increased peak lumbar flexion by approximately 18% and approached 99% of maximum lumbosacral flexion after 20 min, whereas the older group increased lumbar flexion by 4% and approached 82% maximum flexion. The younger group had a larger increase in peak lumbosacral and trunk angular velocities during extension, which may be related to the increased back muscle fatigue observed among the younger group. INTERPRETATION: Older participants appeared to control the detrimental effects of fatigue associated with repetitive lifting and limit lumbar spine range of motion. The higher rates of musculoskeletal injury among older workers may stem from a complex interaction of manual handling risk factors.

Changes of whole-body power, muscle function, and jump performance with prolonged cycling to exhaustion.

PURPOSE: To quantify how whole-body power, muscle-function, and jump-performance measures change during prolonged cycling and recovery and determine whether there are relationships between the different fatigue measures. METHODS: Ten competitive or recreationally active male cyclists underwent repeated 20-min stages of prolonged cycling at 70% VO2peak until exhaustion. Whole-body peak power output (PPO) was assessed using an all-out 30-s sprint 17 min into each cycle stage. Ratings of perceived exertion (RPE) were recorded throughout. Isometric and isokinetic muscle-function tests were made between cycle stages, over ~6 min, and during 30-min recovery. Drop-jump measures were tested at exhaustion and during recovery. RESULTS: PPO initially increased or was maintained in some subjects but fell to 81% of maximum at exhaustion. RPE was near maximal (18.7) at exhaustion, with the time to exhaustion related to the rate of rise of RPE. PPO first started to decline only when RPE exceeded 16 (ie, hard). Peak isometric and concentric isokinetic torque (180°/s) for the quadriceps fell to 86% and 83% of pretest at exhaustion, respectively. In contrast, the peak concentric isokinetic torque (180°/s) of the hamstrings increased by 10% before declining to 93% of maximum. Jump height fell to 92% of pretest at exhaustion and was correlated with the decline in PPO (r = .79). Muscle-function and jump-performance measures did not recover over the 30-min postexercise rest period. CONCLUSIONS: At exhaustion, whole-body power, muscle-function, and jump-performance measures had all fallen by 7-19%. PPO and drop-jump decrements were linearly correlated and are appropriate measures of maximal performance.

The effects of prior exposure, warning, and initial standing posture on muscular and kinematic responses to sudden loading of a hand-held box.

BACKGROUND: Twelve percent of work-related low back injuries have been attributed to sudden loading events. When a sudden load is applied to an object that is held in front of the body, postural responses are rapid, yet it is not clear whether these responses differ with respect to initial posture at the time of loading, or by providing prior exposure to, or warning of a sudden loading event. METHODS: Thirty male subjects in either an upright or stooped standing posture held a pre-weighted box that was suddenly pulled downwards. Surface electromyography techniques were used to detect onset latencies of seven muscles of the right lower limb and trunk, and two-dimensional motion data in the sagittal plane were simultaneously collected. The first trial involved sudden unexpected loading in the upright standing posture, without any prior experience or warning of the loading event. This was followed by a series of randomised loading trials in the upright and stooped standing posture, with and without prior warning of the loading event. FINDINGS: Prior exposure and warning was found to influence postural responses in the upright standing posture, decreasing muscle and joint onset latencies, and resultant maximal angular displacement of the trunk and lower limb. Perturbation in the stooped posture was less reliant on abdominal muscle activation and produced an overall different joint movement initiation pattern, with less joint displacement than in the upright standing position. INTERPRETATION: These findings indicate that prior exposure to, and warning of a sudden loading event lead to changes in postural responses and decreased joint excursion. These changes may contribute to increased stability and decreased risk of musculoskeletal injury.