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We investigated the effect of added load and intense exercise on jump and landing performance and ground reaction force (GRF) during landings where attentional demand was varied. Fifty-two males (37 ± 9.2 years, 180.7 ± 6.1 cm, 90.2 ± 11.6 kg, maximal aerobic fitness (VO(₂max)) 50 ± 8.5 ml (.) kg(-1 .) min(-1), BMI 27.6 ± 3.1, mean ± s) completed a VO(₂max) test. Experimental sessions were completed (≥4 days in between) in a randomised counterbalanced order, one while wearing body armour and appointments (loaded) and one without load (unloaded). A vertical jump, a drop landing concentrating on safe touchdown, a drop jump and a drop landing with an attentional distraction were performed. These were repeated 1 min after a 5-min treadmill run. Mean jump height decreased by 12% (P < 0.001) with loading and a further by 6% following the running task. Peak GRFs were increased by 13-19% with loading (P < 0.001) depending on the landing task demands and a further by 4-9% following intense exercise. The distracted drop landing had significantly higher GRFs compared to all other landings. Results demonstrate that added load impacts on jumping and landing performance, an effect that is amplified by prior intense exercise, and distraction during landing. Such increases in GRF apply to police officer performance in their duties and may increase the risk of injury.

Body armour is used widely by law enforcement and other agencies but has received mixed reviews. This study examined the influence of stab resistant body armour (SRBA) and mandated accessories on physiological responses to, and the performance of, simulated mobility tasks. Fifty-two males (37 ± 9.2 yr, 180.7 ± 6.1 cm, 90.2 ± 11.6 kg, VO2max 50 ± 8.5 ml kg(-1) min(-1), BMI 27.6 ± 3.1, mean ± SD) completed a running VO2max test and task familiarisation. Two experimental sessions were completed (≥4 days in between) in a randomised counterbalanced order, one while wearing SRBA and appointments (loaded) and one without additional load (unloaded). During each session participants performed five mobility tasks: a balance task, an acceleration task that simulated exiting a vehicle, chin-ups, a grappling task, and a manoeuvrability task. A 5-min treadmill run (zero-incline at 13 km·h(-1), running start) was then completed. One min after the run the five mobility tasks were repeated. There was a significant decrease in performance during all tasks with loading (p < 0.001). Participants were off-balance longer; slower to complete the acceleration, grapple and mobility tasks; completed fewer chin-ups; and had greater physiological cost (↑ %HRmax, ↑ %VO2max, ↑ RER) and perceptual effort (↑ RPE) during the 5-min run. Mean performance decreases ranged from 13 to 42% while loaded, with further decreases of 6-16% noted after the 5-min run. Unloaded task performance was no different between phases. Wearing SRBA and appointments significantly reduced mobility during key task elements and resulted in greater physiological effort. These findings could have consequences for optimal function in the working environment and therefore officer and public safety., (Copyright © 2013 Elsevier Ltd and The Ergonomics Society. All rights reserved.)

Objective: Several studies have used the H-reflex to investigate the effect of upright stances and locomotion on spinal reflex excitability. The reliability of eliciting this reflex during weight-bearing has however yet to be addressed. This study was undertaken to determine the reliability of individual differences in the H-reflex recorded from healthy subjects during quiet standing. Secondary aims of the study were to evaluate individual reliability during prolonged standing, and to establish the minimum number of trials required to provide reliable measurements of the H-reflex., Design and Participants: Twenty neurologically healthy volunteers participated in a repeated measures design consisting of 8 blocks of 20 trials evenly distributed over two testing sessions. H-reflex recordings were elicited from the subject's dominant side soleus muscle by percutaneously stimulating the posterior tibial nerve. Stimuli were presented every 10 s, with 2 min seated rest provided between blocks of trials. Peak-to-peak amplitude of H-reflexes and m-responses determined for individual trials were used for subsequent analysis., Results: It was found that the reliability of measuring the H-reflex and m-response during quiet standing was extremely robust (r = .97 for both measures). This pattern of individual differences remained consistent over 80 trials confirming the stability of the measures. High reliabilities (r = .96 and .87 for the H-reflex and m-responses respectively) were also observed when as few as four trials were analysed. When measures obtained during the first session of testing were compared with those obtained for session two, the correlation coefficients were generally of a lower order (r = .54 to .90)., Discussion: The results demonstrate that the H-reflex in quiet standing provides high intra-individual reliability, suggestive of a stable reflex resistant to potentially confounding postural influences, or other sources of biological variation. The between-session reliability underscores the difficulty in reproducing conditions between sessions, and emphasises the need for within-session comparisons of H-reflex amplitudes. Given the functional challenge of maintaining an upright posture, the H-reflex appears to be a well maintained and stable phenomenon.