The influence of rest break frequency and duration on physical performance and psychophysiological responses: a mining simulation study

Abstract

Purpose To investigate the influence of shorter, more frequent rest breaks during simulated work (outdoor mining) in the heat on physical performance and psychophysiological responses. Methods On separate days, thirteen males undertook two 225 min simulation trials in the afternoon (12.00–3.45 pm) including 180 min of treadmill walking at a constant rate of perceived exertion of 11 (or ‘light’) on the 6–20 Borg scale in a heat chamber (37 °C, 40% RH), interspersed with 45 min of rest breaks in an air-conditioned room (22 °C, 35% RH). Rest breaks in the current practice (CP) trial occurred at 1.00 and 2.30 pm (30 min and 15 min, respectively), while in the experimental (EXP) trial were at 1.00 (15 min), 1.45, 2.25 and 3.05 pm (10 min each). Results Total distance covered was not different (p = 0.086) between CP (12,858 ± 2207 m) and EXP (12,094 ± 2174 m). Heart rate, thermal sensation and thermal comfort were significantly higher at 120–180 min (all p < 0.05) in CP compared to EXP. Moderate- to large-effect sizes (Hedge’s g) between trials were also found at 120–180 min for core temperature (g = 0.50 and 0.99, respectively). No differences were found between trials for cognitive performance, perceived fatigue, urine specific gravity, or total water intake (p > 0.05). Conclusion Shorter, more frequent rest breaks have little impact on physical performance, thermal strain and exercise-related sensations. Current practices should remain in place until further studies can be conducted on an actual mine site during summer where outdoor workers perform their work duties.

Work–rest regimens for work in hot environments: A scoping review

“…16 studies that used NIOSH recommendations, two specifically mentioned using the Recommended Alert Limits on unacclimatized participants, 45,58 whereas the other did not mention whether they used the Recommended Alert Limits or the Recommended Exposure Limits but investigated heat-acclimatized 41 Thirty-one experimental studies (89%) focused on physical tasks only (Figure 5A), with 30 studies using endurance tasks and one study using a psychomotor task (one-dimensional vertical compensatory tracking task). 41 One experimental study (3%) 57 investigated mental tasks only (a vertical visual vigilance task), one (3%) 63 investigated endurance and mental tasks sequentially, and two (6%) 16,36 field studies investigated occupational tasks with high cognitive and physical demand (included in "physical and mental, concurrently"). No laboratory study focused on the combination of physical and mental tasks performed concurrently.…”

“…No laboratory study focused on the combination of physical and mental tasks performed concurrently. Of the 33 experimental studies that investigated endurance tasks or a combination of endurance and mental tasks, 25 (76%) used a single-task such as walking, 35,37,40,43,45,47,49,50,52,[59][60][61][63][64][65] cycling, 26-28,39,42,51,62,66 or block stepping. 44,48 The remaining eight studies (24%) incorporated specific occupational tasks related to agriculture, construction, and tourism, 16 welding, 36 repetitive box lifting, 54 walking with load carrying, 49,55,56 walking with arm curls, 58 or walking with shoveling.…”

“…The latter used different techniques to set work intensity (Figure 5C), either by fixing exercise intensity at a given metabolic rate (k = 20, reporting intensity in W, 35,37,40,47,48,54,[58][59][60] in % of VO 2max , 42,43,49,55,64,65 in kcal/ h, 44,52,53 metabolic equivalent of tasks 50 or not reported 56 ), a fixed rate of metabolic heat production, [26][27][28]39,45,51,62,66 or fixing it at a given level of heart rate 61 or perceived effort. 63 Of the 30 experimental studies that used a fixed-intensity strategy, five used various intensity patterns during the simulated work. 40,47,49,50,53 The average total protocol duration, including work and rest periods, was 222 ± 162 min (median: 136, range:…”

“…Specifically, the study by Mortagy and Ramsey 57 did not mention the method used to record core temperature, and Beshir et al 41 did not measure core temperature. Rectal temperature was used in 19 (58%) of the 33 studies, gastrointestinal temperature in six 16,45,[58][59][60]63 (18%) (in two of these studies, some of the participants used rectal temperature due to specific reasons 45,59 ), oral temperature in one, 36 aural canal temperature in one, 65 whereas the others used a combination of rectal and esophageal, 26,42,50,62,66 or rectal and gastrointestinal 51 temperatures.…”

Limitations associated with thermoregulation and cardiovascular research assessing laborers performing work in the heat

“…Out of 1559 potential studies in our search, 21 studies qualified, which yielded 71 interventions (Figure 1). 10,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] No studies were translated using Google Translate. The descriptive characteristics of each intervention are presented in Table 1.…”