Prediction of work metabolism from heart rate measurements in forest work: some practical methodological issues

The Impact of Body Posture on Heart Rate Strain during Tree Felling

Tree felling is recognized as one of the most difficult and physically demanding work phases in motor-manual wood harvesting, during which maintaining good posture can avert unnecessary loadings to the spine and the consequent musculoskeletal disorders to forestry professionals. This study aimed to (a) quantify the impact of posture selection by means of heart rate measurements and (b) analyze its interactions with the anthropometric and personal information of study subjects. Thirteen forest workers were asked to fell thirty trees in each of the four most common body postures during motor-manual forest operations: (i) stooping, (ii) flexed stooping, (iii) squatting, and (iv) half kneeling. Posture had a significant impact on the amount of heart strain measured as mean heart rate during work (HR_work), heart rate increase over resting heart rate (ΔHR), and relative heart rate index (HRR). The most popular position among the forest workers was flexed stooping, which also caused the most damage, compared with the least physiologically damaging position, half kneeling: HR_work by 12.40 bpm, ΔHR by 10.24 bpm, and HRR by 11.51. On the contrary, overweight and older subjects experienced lower heart rate strain, a finding that has to be further investigated.

Assessment of physical work demands of long-distance industrial gas delivery truck drivers

AIM

The aim of this study was to assess the work-related physical demands of long-distance truck drivers employed by a large gas delivery company in Canada.

METHODS

A total of 15 truck drivers participated in a data collection that included self-reporting assessments, field observations, and direct measurements to describe daily tasks organization, postural demands, physical workload, and force exertions.

RESULTS

Truck drivers' work was characterized by long working days ranging from 9.9 to 15.1 h (mean = 11.4 h), with half (49%) of the total working time spent behind the wheel. The overall workload as measured by relative cardiac strain (18.7% RHR) was found excessive for the long term given the shift duration. Peaks of heart rate in excess of 30 beats per minute above the daily average occurred mainly while operating valves and handling heavy hoses during gas deliveries. The task of delivering gas at a client's site required a moderate work rate on average (8.3 mlO₂/kg/min) requiring 24.4% or maximum work capacity on average.

CONCLUSION

Based on multiple data sources, this study highlights the risks of over-exertion and of excessive physical fatigue in the truck drivers' work that are coherent with the high prevalence of self-reported musculoskeletal pain in this group of workers.

Comparison of nine heart rate-based models to predict work metabolism of Forest workers

Predicted work metabolism (WM) from 9 heart rate (HR)-based models were compared to measured WM obtained during work in 39 forest workers. Using measured (i.e. raw) HR in these models can overestimate actual WM since the HR increase associated with body heat accumulation is non-metabolic. Hence, accuracy of WM prediction was assessed on all possible combinations of models using raw HR and corrected HR (thermal component removed) and with five different estimates of maximum work capacity (MWC) for the models that require it as an input. The 50 model combinations produced a wide range of WM estimates. Three models using individual calibration produced the lowest RMSE and narrowest LoA with corrected HR (rRMSE ≤13%; LoA [rBias <5% ± 25%]). One of the models that requires neither determination of the thermal component nor individual calibration performed very well (rRMSE = 18%; LoA [rBias = 1% ± 36%]). Practitioner Summary: These results provide a better understanding of the accuracy of various HR-based work metabolism (WM) estimation models. This information should prove particularly useful to ergonomics professionals wishing to select a method that provides accurate estimation of WM from HR measurements during work in varied thermal environments. Abbreviations: BMI: body mass index; HR: heart rate (beats per min); HR99: HR value exceeded during 99% of the duration of the HR recording period; HRcorr: heart rate without thermal pulses; HRraw: measured heart rate; HRres: heart rate reserve; HRrest: heart rate at rest; LoA: limits of agreement; Mrest: resting metabolism; MWC: maximum work capacity; RMSE: root mean square error; VO2: oxygen consumption; VO2 max: maximum oxygen consumption; WM: work metabolism.

Assessment of physical work demand of short distance industrial gas delivery truck drivers

AIM

This study assessed the work-related physical demands of short-distance truck drivers employed by a large gas delivery company in Canada.

METHODS

A total of 19 truck drivers participated in the data collection, which included a combination of self-reports, field observations and direct measurements to report on the work shift task composition, postures, physical workload, and force exertions.

RESULTS

Driving (mean of 43% of daily work shift) and delivering gas cylinders to customers (28%) were the main tasks of the truck drivers. Delivering gas cylinders measured as moderate level work and daily work duration was not excessive with respect to mean cardiac strain for most drivers. However, manual handling and force exertion activities were frequent and deemed unsafe most of the time with respect to existing guidelines on manual materials handling.

CONCLUSION

This study documents physical risk factors that are consistent with musculoskeletal pain prevalence reported for short-distance truck drivers.

Worker heat stress prevention and work metabolism estimation: comparing two assessment methods of the heart rate thermal component

The heart rate thermal component ( ΔHRT ) can increase with body heat accumulation and lead to work metabolism (WM) overestimation. We used two methods (VOGT and KAMP) to assess ΔHRT of 35 forest workers throughout their work shifts, then compared ΔHRT at work and at rest using limits of agreement (LoA). Next, for a subsample of 20 forest workers, we produced corrected WM estimates from ΔHRT and compared them to measured WM. Although both methods produced significantly different ΔHRT time-related profiles, they yielded comparable average thermal cardiac reactivity (VOGT: 24.8 bpm °C^-1; KAMP: 24.5 bpm °C^-1), average ΔHRT (LoA: 0.7 ± 11.2 bpm) and average WM estimates (LoA: 0.2 ± 3.4 ml O₂ kg^-1min^-1 for VOGT, and 0.0 ± 5.4 ml O₂ kg^-1min^-1 for KAMP). Both methods are suitable to assess heat stress through ΔHRT and improve WM estimation. Practitioner summary: We compared two methods for assessing the heart rate thermal component ( ΔHRT ), which is needed to produce a corrected HR profile for estimating work metabolism (WM). Both methods yielded similar ΔHRT estimates that allowed accurate estimations of heat stress and WM at the group level, but they were imprecise at the individual level. Abbreviations: AIC: akaike information criterion; bpm: beats per minute; CI: confidence intervals; CV: coefficient of variation in %; CV drift: cardiovascular drift; ΔHR_T: the heart rate thermal component in bpm; ΔHR_T: the heart rate thermal component in bpm; ΔΔHR_T: variation in the heart rate thermal component in bpm; ΔT_C: variation in core body temperature in °C; HR: heart rate in bpm; HRmax: maximal heart rate in bpm; Icl: cloting insulation in clo; KAMP: Kampmann et al. (2001) method to determe ΔHR_T; LoA: Limits of Agreement; PMV-PPD: the Predicted Mean Vote and Predicted Percentage Dissatisfied; PHS: Predicted Heat Strain model; RCM: random coefficients model; SD: standard deviation; TC: core body temperature in °C; TCR: thermal cardiac reactivity in bpm °C^-1; τ_ΔHRT: rate of change in the heart rate thermal component in bpm min^-1; τ_TC: rate of change in core body temperature in °C min^-1; t_α,n-1: Student's t statistic with level of confidence alpha and n^-1 degrees of freedom; TWL: Thermal Work Limit model; V̇O2 : oxygen consumption in ml O₂ kg^-1 min^-1; V̇O2 max: maximal oxygen consumption in ml O₂ kg^-1 min^-1; VOGT: Vogt et al. (1973) method to determine ΔHR_T; WBGT: Wet-Bulb Globe Temperature in °C; WM: work metabolism.

Evaluation of physiological workload assessment methods using heart rate and accelerometry for a smart wearable system

Work metabolism (WM) can be accurately estimated by oxygen consumption (VO₂), which is commonly assessed by heart rate (HR) in field studies. However, the VO₂-HR relationship is influenced by individual capacity and activity characteristics. The purpose of this study was to evaluate three models for estimating WM compared with indirect calorimetry, during simulated work activities. The techniques were: the HR-Flex model; HR branched model, combining HR with hip-worn accelerometers (ACC); and HR + arm-leg ACC model, combining HR with wrist- and thigh-worn ACC. Twelve participants performed five simulated work activities and three submaximal tests. The HR + arm-leg ACC model had the overall best performance with limits of agreement (LoA) of -3.94 and 2.00 mL/min/kg, while the HR-Flex model had -5.01 and 5.36 mL/min/kg and the branched model, -6.71 and 1.52 mL/min/kg. In conclusion, the HR + arm-leg ACC model should, when feasible, be preferred in wearable systems for WM estimation. Practitioner Summary: Work with high energy demand can impair employees' health and life quality. Three models were evaluated for estimating work metabolism during simulated tasks. The model combining heart rate, wrist- and thigh-worn accelerometers showed the best accuracy. This is, when feasible, suggested for wearable systems to assess work metabolism.