Occupational cold stress and rewarming alters skin temperature thresholds for manual dexterity decrements: An exploratory study

Abstract

The skin temperature thresholds at which precipitous reductions in dexterity occur in cold environments, and whether they are altered by rewarming, are not well defined. In three environmental conditions (20°C, 10°C, and 0°C air temperatures), 14 healthy adults (three females; age: 24 ± 6 years) completed five dexterity tests (Placing Test) over ~130 min of various light-to-moderate physical activities to simulate occupational work demands while minimally dressed. Brief passive rewarming (10 min in ~22°C air temperature) and a final dexterity test upon reentry to the environment was then performed. Dexterity was evaluated as the absolute (seconds) or percent change from an individual's best baseline performance. Prior to rewarming, segmented regression revealed thresholds for greater dexterity loss during progressive cold strain occurred at skin temperatures of ~22.9°C (fingers), ~24.9°C (hand), and ~22.4°C (forearm) (all p ≤ 0.002). After rewarming, this threshold shifted upwards to ~25.7°C for the fingers (p ≤ 0.007). The hand skin temperature threshold after rewarming was ~27.1°C (for absolute changes, p < 0.001), but one was not identified with percent change (p = 0.074). A forearm skin temperature threshold was not identified following rewarming (p ≥ 0.058). These findings indicate that, in non-hypothermic conditions, skin temperature thresholds for dexterity loss during prolonged occupational cold stress may be modified with rewarming.

Keywords: cold injury; environmental; fingers; hands; work‐rest.

FIGURE 1

Representative example of one participant in a 0°C trial. Individuals participated in three experimental trials that differed only by air temperature (20°C, 10°C, and 0°C). Participants (3 females and 11 males) engaged in ~130 min of physical activity where dexterity was assessed at five timepoints (DT1–5) throughout the exposure, followed by a 10‐min seated passive rewarming period (~22°C air temperature), and ending with a final dexterity assessment (DT6) upon re‐entry to the cold environment. Physical activity consisted of 4 cycles of a ~10 min performance battery with 20 min treadmill walking at varying speeds and grades [walk 1–4], after which a final performance battery was performed. The performance batteries consisted of 3 sets of 1 repetition (3 × 1) of squat jumps (30‐s rest between repetitions), 3 × 1 isometric mid‐thigh pull (30‐s rest between repetitions), seated dexterity test, and 1 × 3 maximal isometric handgrip strength on each hand (15‐s rest between repetitions). Representative finger skin temperature, core temperature, and heart rate data from one participant's 0°C trial are shown to highlight the modest increases in core temperature and reductions in finger skin temperature that occurred with varying exercise intensities throughout the trial.

FIGURE 2

Descriptive individual physiological responses to occupational cold stress and rewarming. Participants engaged in ~130 min of physical activity in the cold in which dexterity was assessed at five timepoints throughout the exposure, followed by a 10‐min passive rewarming period, and ending with a final dexterity assessment upon re‐entry to the cold environment. Individuals participated in three experimental trials that differed only by air temperature 20°C, 10°C, and 0°C). The dashed lined separates baseline values prior to insertion in the cold environment (on the left) and values across time during the prolonged cold exposure, rewarming period, and subsequent reinsertion into the cold environment (on the right). Individual data are presented by lines. Circles on the right of the dashed line depict when the dexterity tests occurred for a given participant (six total per a given environmental condition). Note that thermal sensation was not measured prior to insertion into the cold environment. n = 14 (3 females and 11 males).

FIGURE 3

Finger skin temperature thresholds for greater losses of dexterity during occupational cold stress. Participants engaged in ~130 min of light‐to‐moderate physical activity in the cold in which dexterity was assessed at five timepoints throughout the exposure (Before Rewarming, panels a and b), followed by a 10‐min passive rewarming period, and ending with a final dexterity assessment upon re‐entry to the cold environment (After Rewarming, panels c and d). The change (∆) in the time to complete the dexterity test compared to a given participant's best performance during a baseline visit is expressed in seconds (Panels a and c) or percent change (Panels b and d). Main panels display the statistical threshold point estimate with standard error (dashed line with gray shading and values presented), with model fit from segmented regression in green (mean with 95% confidence intervals) and best model fit after the threshold by polynomial regression (R ² values presented) in blue (mean with 95% confidence intervals). Inset figures show the same data for a given panel with the application of a locally estimated scatterplot smoothing curve to aid visualization. n = 14 (3 females and 11 males).

FIGURE 4

Hand skin temperature thresholds for greater losses of dexterity during occupational cold stress. Participants engaged in ~130 min of light‐to‐moderate physical activity in the cold in which dexterity was assessed at five timepoints throughout the exposure (Before Rewarming, panels a and b), followed by a 10‐min passive rewarming period, and ending with a final dexterity assessment upon re‐entry to the cold environment (After Rewarming, panels c and d). The change (∆) in the time to complete the dexterity test compared to a given participant's best performance during a baseline visit is expressed in seconds (Panels a and c) or percent change (Panels b and d). Main panels display the statistical threshold point estimate with standard error (dashed line with gray shading and values presented), with model fit from segmented regression in green (mean with 95% confidence intervals) and best model fit after the threshold by polynomial regression (R ² values presented) in blue (mean with 95% confidence intervals). Inset figures show the same data for a given panel with the application of a locally estimated scatterplot smoothing curve to aid visualization. n = 14 (3 females and 11 males).

FIGURE 5

Forearm skin temperature thresholds for greater losses of dexterity during occupational cold stress. Participants engaged in ~130 min of light‐to‐moderate physical activity in the cold in which dexterity was assessed at five timepoints throughout the exposure (Before Rewarming, panels a and b), followed by a 10‐min passive rewarming period, and ending with a final dexterity assessment upon re‐entry to the cold environment (After Rewarming, panels c and d). The change (∆) in the time to complete the dexterity test compared to a given participant's best performance during a baseline visit is expressed in seconds (Panels a and c) or percent change (Panels b and d). Main panels display the statistical threshold point estimate with standard error (dashed line with gray shading and values presented), with model fit from segmented regression in green (mean with 95% confidence intervals) and best model fit after the threshold by polynomial regression (R ² values presented) in blue (mean with 95% confidence intervals). Inset figures show the same data for a given panel with the application of a locally estimated scatterplot smoothing curve to aid visualization. n = 14 (3 females and 11 males).

FIGURE 6

Diagnostic accuracy of skin temperature, core temperature, and thermal sensation for discriminating dexterity loss during cold exposure and rewarming. Participants engaged in ~130 min of physical activity in the cold in which dexterity was assessed at five timepoints throughout the exposure, followed by a 10‐min passive rewarming period, and ending with a final dexterity assessment upon re‐entry to the cold environment. The ability of cold strain measurements to discriminate a 5% (left panel) or 10% (right panel) loss of dexterity is plotted as the area under the curve with 95% confidence intervals from receiver operating characteristic curves constructed from a generalized linear mixed effects model to account for repeated measures. Diagnostic accuracy for dexterity was assessed with inclusion of the rewarming data (i.e., all six dexterity tests) or exclusion of the rewarming data (i.e., dexterity tests 1–5). TCore, core temperature; Ts4thFinger, 4th finger skin temperature; TSensation, thermal sensation; TsHand, hand skin temperature. n = 14 (3 females and 11 males).