Ollie Jay

Physical work capacity in older adults: Implications for the aging worker

BACKGROUND In many developed countries, the workforce is rapidly aging. Occupational demands however, have not decreased despite the fact that workers see a decline in physical work capacity with age. The purpose of this review is to examine the physiological adaptations to aging, the impact of aging on performance and the benefits of physical fitness in improving functional work capacity in aging individuals. METHODS An extensive search of the scientific literature was performed, acquiring published articles which examined the physiological changes associated with age-related decrements in the physical work capacity of healthy aging adults. The databases accessed included AARP Ageline, AccessScience, Annual Reviews, CISTI, Cochrane Library, Clinical Evidence, Digital Dissertations (Proquest), Embase, HealthSTAR, Medline, PubMed, Scopus, and PASCAL and included relevant information sites obtained on the world wide web. RESULTS While a great deal of variation exists, an average decline of 20% in physical work capacity has been reported between the ages of 40 and 60 years, due to decreases in aerobic and musculoskeletal capacity. These declines can contribute to decreased work capacity, and consequential increases in work-related injuries and illness. However, differences in habitual physical activity will greatly influence the variability seen in individual physical work capacity and its components. Well-organized, management-supported, work-site health interventions encouraging physical activity during work hours could potentially decrease the incidence of age-related injury and illness. CONCLUSIONS Age-associated functional declines and the accompanying risk of work-related injury can be prevented or at least delayed by the practice of regular physical activity. Older workers could optimally pursue their careers until retirement if they continuously maintain their physical training.

Heat stress in older individuals and patients with common chronic diseases

Scientists have predicted that extremes in climate are likely to increase in frequency and severity. [1][1] These changes may have a direct impact on population health, as heat waves can exceed the physiological adaptive capacity of vulnerable population groups. Individuals over the age of 60 years

Thermometry, Calorimetry, and Mean Body Temperature during Heat Stress

Heat balance in humans is maintained at near constant levels through the adjustment of physiological mechanisms that attain a balance between the heat produced within the body and the heat lost to the environment. Heat balance is easily disturbed during changes in metabolic heat production due to physical activity and/or exposure to a warmer environment. Under such conditions, elevations of skin blood flow and sweating occur via a hypothalamic negative feedback loop to maintain an enhanced rate of dry and evaporative heat loss. Body heat storage and changes in core temperature are a direct result of a thermal imbalance between the rate of heat production and the rate of total heat dissipation to the surrounding environment. The derivation of the change in body heat content is of fundamental importance to the physiologist assessing the exposure of the human body to environmental conditions that result in thermal imbalance. It is generally accepted that the concurrent measurement of the total heat generated by the body and the total heat dissipated to the ambient environment is the most accurate means whereby the change in body heat content can be attained. However, in the absence of calorimetric methods, thermometry is often used to estimate the change in body heat content. This review examines heat exchange during challenges to heat balance associated with progressive elevations in environmental heat load and metabolic rate during exercise. Further, we evaluate the physiological responses associated with heat stress and discuss the thermal and nonthermal influences on the bodys ability to dissipate heat from a heat balance perspective.

The evaporative requirement for heat balance determines whole‐body sweat rate during exercise under conditions permitting full evaporation

•  A relative exercise intensity (%) protocol is often used to compare absolute whole‐body sweat rates (WBSRs) during exercise between participants of different aerobic capacity. •  Under conditions permitting full evaporation, heat balance theory suggests that exercise intensity should be fixed to elicit the same rate of evaporation required for heat balance (Ereq). •  Whole‐body direct calorimetry was employed to measure WBSRs throughout 90 min of exercise across a range of air temperatures and rates of metabolic heat production. •  Irrespective of ambient temperature and metabolic heat production, Ereq alone described ∼90% of all variability in WBSR during steady‐state and non‐steady‐state exercise, whereas <2% of variation was independently described by %. •  To perform an unbiased comparison of WBSRs (but not necessarily core temperature) between different individuals/groups under conditions allowing full evaporation, future studies should consider using a fixed Ereq irrespective of the % incurred.

Large differences in peak oxygen uptake do not independently alter changes in core temperature and sweating during exercise.

The independent influence of peak oxygen uptake (Vo(₂ peak)) on changes in thermoregulatory responses during exercise in a neutral climate has not been previously isolated because of complex interactions between Vo(₂ peak), metabolic heat production (H(prod)), body mass, and body surface area (BSA). It was hypothesized that Vo(₂ peak) does not independently alter changes in core temperature and sweating during exercise. Fourteen males, 7 high (HI) Vo(₂ peak): 60.1 ± 4.5 ml·kg⁻¹·min⁻¹; 7 low (LO) Vo(₂ peak): 40.3 ± 2.9 ml·kg⁻¹·min⁻¹ matched for body mass (HI: 78.2 ± 6.1 kg; LO: 78.7 ± 7.1 kg) and BSA (HI: 1.97 ± 0.08 m²; LO: 1.94 ± 0.08 m²), cycled for 60-min at 1) a fixed heat production (FHP trial) and 2) a relative exercise intensity of 60% Vo(₂ peak) (REL trial) at 24.8 ± 0.6°C, 26 ± 10% RH. In the FHP trial, H(prod) was similar between the HI (542 ± 38 W, 7.0 ± 0.6 W/kg or 275 ± 25 W/m²) and LO (535 ± 39 W, 6.9 ± 0.9 W/kg or 277 ± 29 W/m²) groups, while changes in rectal (T(re): HI: 0.87 ± 0.15°C, LO: 0.87 ± 0.18°C, P = 1.00) and aural canal (T(au): HI: 0.70 ± 0.12°C, LO: 0.74 ± 0.21°C, P = 0.65) temperature, whole-body sweat loss (WBSL) (HI: 434 ± 80 ml, LO: 440 ± 41 ml; P = 0.86), and steady-state local sweating (LSR(back)) (P = 0.40) were all similar despite relative exercise intensity being different (HI: 39.7 ± 4.2%, LO: 57.6 ± 8.0% Vo(2 peak); P = 0.001). At 60% Vo(2 peak), H(prod) was greater in the HI (834 ± 77 W, 10.7 ± 1.3 W/kg or 423 ± 44 W/m²) compared with LO (600 ± 90 W, 7.7 ± 1.4 W/kg or 310 ± 50 W/m²) group (all P < 0.001), as were changes in T(re) (HI: 1.43 ± 0.28°C, LO: 0.89 ± 0.19°C; P = 0.001) and T(au) (HI: 1.11 ± 0.21°C, LO: 0.66 ± 0.14°C; P < 0.001), and WBSL between 0 and 15, 15 and 30, 30 and 45, and 45 and 60 min (all P < 0.01), and LSR(back) (P = 0.02). The absolute esophageal temperature (T(es)) onset for sudomotor activity was ∼0.3°C lower (P < 0.05) in the HI group, but the change in T(es) from preexercise values before sweating onset was similar between groups. Sudomotor thermosensitivity during exercise were similar in both FHP (P = 0.22) and REL (P = 0.77) trials. In conclusion, changes in core temperature and sweating during exercise in a neutral climate are determined by H(prod), mass, and BSA, not Vo(₂ peak).

Selecting the correct exercise intensity for unbiased comparisons of thermoregulatory responses between groups of different mass and surface area

We assessed whether comparisons of thermoregulatory responses between groups unmatched for body mass and surface area (BSA) should be performed using a metabolic heat production (prod) in Watts or Watts per kilogram for changes in rectal temperature (ΔTre), and an evaporative heat balance requirement (Ereq) in Watts or Watts per square meter for local sweat rates (LSR). Two groups with vastly different mass and BSA [large (LG): 91.5 ± 6.8 kg, 2.12 ± 0.09 m(2), n = 8; small (SM): 67.6 ± 5.6 kg, 1.80 ± 0.09 m(2), n = 8; P < 0.001], but matched for heat acclimation status, sex, age, and with the same onset threshold esophageal temperatures (LG: +0.37 ± 0.12°C; SM: +0.41 ± 0.17°C; P = 0.364) and thermosensitivities (LG: 1.02 ± 0.54, SM: 1.00 ± 0.38 mg·cm(-2)·min(-1)·°C(-1); P = 0.918) for sweating, cycled for 60 min in 25°C at different levels of prod (500 W, 600 W, 6.5 W/kg, 9.0 W/kg) and Ereq (340 W, 400 W, 165 W/m(2), 190 W/m(2)). ΔTre was different between groups at a prod of 500 W (LG: 0.52 ± 0.15°C, SM: 0.92 ± 0.24°C; P < 0.001) and 600 W (LG: 0.78 ± 0.19°C, SM: 1.14 ± 0.24°C; P = 0.007), but similar at 6.5 W/kg (LG: 0.79 ± 0.21°C, SM: 0.85 ± 0.14°C; P = 0.433) and 9.0 W/kg (LG: 1.02 ± 0.22°C, SM: 1.14 ± 0.24°C; P = 0.303). Furthermore, ΔTre was the same at 9.0 W/kg in a 35°C environment (LG: 1.12 ± 0.30°C, SM: 1.14 ± 0.25°C) as at 25°C (P > 0.230). End-exercise LSR was different at Ereq of 400 W (LG: 0.41 ± 0.18, SM: 0.57 ± 0.13 mg·cm(-2)·min(-1); P = 0.043) with a trend toward higher LSR in SM at 340 W (LG: 0.28 ± 0.06, SM: 0.37 ± 0.15 mg·cm(-2)·min(-1); P = 0.057), but similar at 165 W/m(2) (LG: 0.28 ± 0.06, SM: 0.28 ± 0.12 mg·cm(-2)·min(-1); P = 0.988) and 190 W/m(2) (LG: 0.41 ± 0.18, SM: 0.37 ± 0.15 mg·cm(-2)·min(-1); P = 0.902). In conclusion, when comparing groups unmatched for mass and BSA, future experiments can avoid systematic differences in ΔTre and LSR by using a fixed prod in Watts per kilogram and Ereq in Watts per square meter, respectively.

Heat exposure in the Canadian workplace

Exposure to excessive heat is a physical hazard that threatens Canadian workers. As patterns of global climate change suggest an increased frequency of heat waves, the potential impact of these extreme climate events on the health and well-being of the Canadian workforce is a new and growing challenge. Increasingly, industries rely on available technology and information to ensure the safety of their workers. Current Canadian labor codes in all provinces employ the guidelines recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) that are Threshold Limit Values (TLVs) based upon Wet Bulb Globe Temperature (WBGT). The TLVs are set so that core body temperature of the workers supposedly does not exceed 38.0 degrees C. Legislation in most Canadian provinces also requires employers to install engineering and administrative controls to reduce the heat stress risk of their working environment should it exceed the levels permissible under the WBGT system. There are however severe limitations using the WGBT system because it only directly evaluates the environmental parameters and merely incorporates personal factors such as clothing insulation and metabolic heat production through simple correction factors for broadly generalized groups. An improved awareness of the strengths and limitations of TLVs and the WGBT index can minimize preventable measurement errors and improve their utilization in workplaces. Work is on-going, particularly in the European Union to develop an improved individualized heat stress risk assessment tool. More work is required to improve the predictive capacity of these indices.

Calorimetric measurement of postexercise net heat loss and residual body heat storage.

PURPOSE Previous studies have shown a rapid reduction in postexercise local sweating and blood flow despite elevated core temperatures. However, local heat loss responses do not illustrate how much whole-body heat dissipation is reduced, and core temperature measurements do not accurately represent the magnitude of residual body heat storage. Whole-body evaporative (H(E)) and dry (H(D)) heat loss as well as changes in body heat content (DeltaH(b)) were measured using simultaneous direct whole-body and indirect calorimetry. METHODS Eight participants cycled for 60 min at an external work rate of 70 W followed by 60 min of recovery in a calorimeter at 30 degrees C and 30% relative humidity. Core temperature was measured in the esophagus (T(es)), rectum (T(re)), and aural canal (T(au)). Regional muscle temperature was measured in the vastus lateralis (T(vl)), triceps brachii (T(tb)), and upper trapezius (T(ut)). RESULTS After 60 min of exercise, average DeltaH(b) was +273 +/- 57 kJ, paralleled by increases in T(es), T(re), and T(au) of 0.84 +/- 0.49, 0.67 +/- 0.36, and 0.83 +/- 0.53 degrees C, respectively, and increases in T(vl), T(tb), and T(ut) of 2.43 +/- 0.60, 2.20 +/- 0.64, and 0.80 +/- 0.20 degrees C, respectively. After a 10-min recovery, metabolic heat production returned to pre-exercise levels, and H(E) was only 22.9 +/- 6.9% of the end-exercise value despite elevations in all core temperatures. After a 60-min recovery, DeltaH(b) was +129 +/- 58 kJ paralleled by elevations of T(es) = 0.19 +/- 0.13 degrees C, T(re) = 0.20 +/- 0.03 degrees C, T(au) = 0.18 +/- 0.04 degrees C, Tvl = 1.00 +/- 0.43 degrees C, T(tb) = 0.92 +/- 0.46 degrees C, and T(ut) = 0.31 +/- 0.27 degrees C. Despite this, H(E) returned to preexercise levels. Only minimal changes in H(D) occurred throughout. CONCLUSION We confirm a rapid reduction in postexercise whole-body heat dissipation by evaporation despite elevated core temperatures. Consequently, only 53% of the heat stored during 60 min of exercise was dissipated after 60 min of recovery, with the majority of residual heat stored in muscle tissue.

Consensus recommendations on training and competing in the heat

Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up‐to‐date recommendations to optimize performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimize performance is to heat acclimatize. Heat acclimatization should comprise repeated exercise‐heat exposures over 1–2 weeks. In addition, athletes should initiate competition and training in a euhydrated state and minimize dehydration during exercise. Following the development of commercial cooling systems (e.g., cooling vest), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organizers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimizing the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events for hydration and body cooling opportunities when competitions are held in the heat.

Aural canal, esophageal, and rectal temperatures during exertional heat stress and the subsequent recovery period.

CONTEXT The measurement of body temperature is crucial for the initial diagnosis of exertional heat injury and for monitoring purposes during a subsequent treatment strategy. However, little information is available about how different measurements of body temperature respond during and after exertional heat stress. OBJECTIVE To present the temporal responses of aural canal (T(ac)), esophageal (T(es)), and rectal (T(re)) temperatures during 2 different scenarios (S1, S2) involving exertional heat stress and a subsequent recovery period. DESIGN Randomized controlled trial. SETTING University research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty-four healthy volunteers, with 12 (5 men, 7 women) participating in S1 and 12 (7 men, 5 women) participating in S2. INTERVENTION(S) The participants exercised in the heat (42 degrees C, 30% relative humidity) until they reached a 39.5 degrees C cut-off criterion, which was determined by T(re) in S1 and by T(es) in S2. As such, participants attained different levels of hyperthermia (as determined by T(re)) at the end of exercise. Participants in S1 were subsequently immersed in cold water (2 degrees C) until T(re) reached 37.5 degrees C, and participants in S2 recovered in a temperate environment (30 degrees C, 30% relative humidity) for 60 minutes. MAIN OUTCOME MEASURE(S) We measured T(ac), T(es), and T(re) throughout both scenarios. RESULTS The T(es) (S1 = 40.19 +/- 0.41 degrees C, S2 = 39.50 +/- 0.02 degrees C) was higher at the end of exercise compared with both T(ac) (S1 = 39.74 +/- 0.42 degrees C, S2 = 38.89 +/- 0.32 degrees C) and T(re) (S1 = 39.41 +/- 0.04 degrees C, S2 = 38.74 +/- 0.28 degrees C) (for both comparisons in each scenario, P < .001). Conversely, T(es) (S1 = 36.26 +/- 0.74 degrees C, S2 = 37.36 +/- 0.34 degrees C) and T(ac) (S1 = 36.48 +/- 1.07 degrees C, S2 = 36.97 +/- 0.38 degrees C) were lower compared with T(re) (S1 = 37.54 +/- 0.04 degrees C, S2 = 37.78 +/- 0.31 degrees C) at the end of both scenarios (for both comparisons in each scenario, P < .001). CONCLUSIONS We found that T(ac), T(es), and T(re) presented different temporal responses during and after both scenarios of exertional heat stress and a subsequent recovery period. Although these results may not have direct practical implications in the field monitoring and treatment of individuals with exertional heat injury, they do quantify the extent to which these body temperature measurements differ in such scenarios.