Cooling Modality Effectiveness and Mortality Associate With Prehospital Care of Exertional Heat Stroke Casualities

BACKGROUND

Cold-water immersion is the gold standard for field treatment of an exertional heat stroke (EHS) casualty. Practical limitations may preclude this method and ice sheets (bed linens soaked in ice water) have emerged as a viable alternative. Laboratory studies suggest that this is an inferior method; however, the magnitude of hyperthermia is limited and may underestimate the cooling rate in EHS casualties.

OBJECTIVE

Our aim was to determine the prehospital core cooling rate, need for continued cooling on arrival to the emergency department, and mortality rate associated with ice sheet use.

METHODS

De-identified retrospective data were obtained from emergency medical services (EMS) and included presence or absence of altered mental status, cooling measures applied prior to EMS arrival, and time and core temperature (T_c; rectal) on-scene and on hospital arrival. Cooling rate was calculated from time and temperature data. Mortality data were obtained from the U.S. Army Combat Readiness Center.

RESULTS

There were 462 casualties that met inclusion criteria. The cooling rate for the entire sample was 0.07°C ± 0.08°C · min^-1. EHS casualties with an observed initial T_c < 39°C had an en route cooling rate of 0.03°C ± 0.04°C · min^-1 vs. initial T_c ≥ 39°C cooling rate of 0.16°C ± 0.08°C · min^-1. There was one fatality due to EHS, for a mortality rate of 0.20% (95% CI 0.01-1.20%).

CONCLUSIONS

The cooling rate in EHS casualties with initial T_c ≥ 39°C was approximately double that reported in laboratory studies. The observed mortality rate was comparable with casualties treated with cold-water immersion. Our data suggest that ice sheets provide a viable alternative when practical constraints preclude cold-water immersion.

Exertional heat stroke: An evidence based approach to clinical assessment and management

NEW FINDINGS

What is the topic of this review? The treatment of exertional heat stress, from initial field care through the return-to-activity decision, is reviewed. What advances does it highlight? Clinical assessment during field care using AVPU and vital signs to gauge recovery Approaches to field cooling and end of active cooling Shared clinical decision making for return to activity recommendations ABSTRACT: Exertional heat stroke (EHS) is a potentially fatal condition characterized by central nervous system dysfunction and body temperature often but not always >40°C that occurs in the context of physical work in warm or hot environments. In this paper, we review the continuum of care, from initial recognition and field care to transport and hospital care, and finally return to duty considerations. Morbidity and mortality can be greatly reduced if not eliminated with prompt recognition and aggressive cooling. If medical personnel are not present at point of collapse during or immediately following exercise, EHS should be the presumptive diagnosis until a formal diagnosis can be determined by qualified medical staff. EHS is the rare medical situation where initial treatment (cooling) takes precedence over transport to a medical facility, where advanced medical care may be required for severe EHS casualties. Recovery from EHS and return to activity is usually straightforward and unremarkable provided the casualty is rapidly cooled at time of collapse and adequate time is allowed for body healing. However, evidence-based data to guide return to activity following EHS is limited. Current research suggests that most individuals recover completely within a few weeks though some individuals may suffer prolonged sequalae and additional evaluation may be warranted, including heat tolerance testing. Several aspects of the care of the EHS casualty are based on best practices derived from personal experience and continued research is necessary to optimize evaluation and management. This article is protected by copyright. All rights reserved.

Heat Safety in the Workplace: Modified Delphi Consensus to Establish Strategies and Resources to Protect the US Workers

The purpose of this consensus document was to develop feasible, evidence-based occupational heat safety recommendations to protect the US workers that experience heat stress. Heat safety recommendations were created to protect worker health and to avoid productivity losses associated with occupational heat stress. Recommendations were tailored to be utilized by safety managers, industrial hygienists, and the employers who bear responsibility for implementing heat safety plans. An interdisciplinary roundtable comprised of 51 experts was assembled to create a narrative review summarizing current data and gaps in knowledge within eight heat safety topics: (a) heat hygiene, (b) hydration, (c) heat acclimatization, (d) environmental monitoring, (e) physiological monitoring, (f) body cooling, (g) textiles and personal protective gear, and (h) emergency action plan implementation. The consensus-based recommendations for each topic were created using the Delphi method and evaluated based on scientific evidence, feasibility, and clarity. The current document presents 40 occupational heat safety recommendations across all eight topics. Establishing these recommendations will help organizations and employers create effective heat safety plans for their workplaces, address factors that limit the implementation of heat safety best-practices and protect worker health and productivity.

Seasonal Trends for Environmental Illness Incidence in the U.S. Army

INTRODUCTION

The incidence of and risk factors for exertional heat illness (EHI) and cold weather injury (CWI) in the U.S. Army have been well documented. The "heat season", when the risk of EHI is highest and application of risk mitigation procedures is mandatory, has been arbitrarily defined as May 1 through September 30, while the "cold season" is understood to occur from October 1 to April 30 each year. The proportions of EHI and CWI that occur outside of the traditional heat and cold seasons are unknown. Additionally, it is unknown if either of the seasonal definitions are appropriate. The primary purpose of this study was to determine the proportion of EHI and of CWI that occur within the commonly accepted seasonal definitions. We also report the location-specific variability, seasonal definitions, and the demographic characteristics of the populations.

METHODS

The U.S. Army installations with the highest frequency of EHI and of CWI from 2008 to 2013 were identified and used for analysis. In total there were 15 installations included in the study, with five installations used for analysis in both the EHI and CWI projects. In- and out-patient EHI and CWI data (ICD-9-CM codes 992.0 to 992.9 and ICD codes 991.0 to 991.9, respectively) were obtained from the Defense Medical Surveillance System. Installation-specific denominator data were obtained from the Defense Manpower Data Center, and incidence rates were calculated by week, for each installation. Segmental (piecewise) regression analysis was used to determine the start and end of the heat and cold seasons.

RESULTS

Our analysis indicates that the heat season starts around April 22 and ends around September 9. The cold season starts on October 3 and ends on March 24. The majority (n = 6,445, 82.3%) of EHIs were diagnosed during the "heat season" of May 1 to September 30, while 10.3% occurred before the heat season started (January1 to April 30) and 7.3% occurred after the heat season ended (October 1 to December 31). Similar to EHI, 90.5% of all CWIs occurred within the traditionally defined cold season, while 5.7% occurred before and 3.8% occurred after the cold season. The locations with the greatest EHI frequency were Ft Bragg (n = 2,129), Ft Benning (n = 1,560), and Ft Jackson (n = 1,538). The bases with the largest proportion of CWI in this sample were Ft Bragg (17.8%), Ft Wainwright (17.2%), and Ft Jackson (12.7%). There were considerable inter-installation differences for the start and end dates of the respective seasons.

CONCLUSIONS

The present study indicates that the traditional heat season definition should be revised to begin  ∼3 weeks earlier than the current date of May 1; our data indicate that the current cold season definition is appropriate. Inter-installation variability in the start of the cold season was much larger than that for the heat season. Exertional heat illnesses are a year-round problem, with ∼17% of all cases occurring during non-summer months, when environmental heat strain and vigilance are lower. This suggests that EHI mitigation policies and procedures require greater year-round emphasis, particularly at certain locations.

International Classification of Disease Coding of Exertional Heat Illness in U.S. Army Soldiers

INTRODUCTION

The severity of exertional heat illnesses (EHI) ranges from relatively minor heat exhaustion to potentially life-threatening heat stroke. Epidemiological surveillance of the types of and trends in EHI incidence depends on application of the appropriate International Classification of Disease, 9th Revision (ICD-9) diagnostic code. However, data examining whether the appropriate EHI ICD-9 code is selected are lacking. The purpose of this study was to determine whether the appropriate ICD-9 code is selected in a cohort of EHI casualties.

MATERIALS AND METHODS

Chart reviews of 290 EHI casualties that occurred in U.S. Army soldiers from 2009 to 2012 were conducted. The ICD-9 diagnostic code was extracted, as were the initial and peak values for aspartate transaminase, alanine transaminase, creatine kinase, and creatinine. Diagnostic criteria for heat injury and heat stroke include evidence of organ and/or tissue damage; 2 out of 3 of the following must have been met to be considered heat injury (ICD-9 code 992.8) or heat stroke (ICD-9 code 992.0): aspartate transaminase/ alanine transaminase fold increase >3, creatine kinase fold increase >5, and/or creatinine ≥1.5mg/dL. Contingency tables were constructed from which sensitivity, specificity, and positive and negative predictive value were calculated.

RESULTS

The 290 cases in this cohort represent ∼29% of all EHI at Fort Benning and ∼6% of all EHI Army-wide during the study period. There were 80 cases that met the laboratory diagnostic criteria for heat injury/stroke, however of those, 28 cases were diagnosed as an EHI other than heat injury/stroke (sensitivity = 0.65). 210 cases did not meet the laboratory diagnostic criteria, but 66 of those were incorrectly diagnosed as heat injury or heat stroke (specificity = 0.69). Positive and negative predictive values were 0.44 and 0.84, respectively. In total, the incorrect ICD-9 code was applied to 94 of 290 total cases.

CONCLUSIONS

Our data suggest that caution is warranted when examining epidemiological surveillance data on EHI severity, as there was disagreement between the laboratory data and the selected ICD-9 code in ∼1/3 of all cases in this cohort. Of note is the lack of an ICD-9 or -10 code for heat injury; we recommend coding for heat exhaustion as the primary diagnosis and additional codes to capture the accompanying muscle, tissue, and/or organ damage.

Fitness tests and occupational tasks of military interest: a systematic review of correlations

: Physically demanding occupations (ie, military, firefighter, law enforcement) often use fitness tests for job selection or retention. Despite numerous individual studies, the relationship of these tests to job performance is not always clear. : This review examined the relationship by aggregating previously reported correlations between different fitness tests and common occupational tasks. : Search criteria were applied to PUBMED, EBSCO, EMBASE and military sources; scoring yielded 27 original studies providing 533 Pearson correlation coefficients (r) between fitness tests and 12 common physical job task categories. Fitness tests were grouped into predominant health-related fitness components and body regions: cardiorespiratory endurance (CRe); upper body, lower body and trunk muscular strength and muscular endurance (UBs, LBs, TRs, UBe, LBe, TRe) and flexibility (FLX). Meta-analyses provided pooled r's between each fitness component and task category. : The CRe tests had the strongest pooled correlations with most tasks (eight pooled r values 0.80-0.52). Next were LBs (six pooled r values >0.50) and UBe (four pooled r values >0.50). UBs and LBe correlated strongly to three tasks. TRs, TRe and FLX did not strongly correlate to tasks. : Employers can maximise the relevancy of assessing workforce health by using fitness tests with strong correlations between fitness components and job performance, especially those that are also indicators for injury risk. Potentially useful field-expedient tests include timed-runs (CRe), jump tests (LBs) and push-ups (UBe). Impacts of gender and physiological characteristics (eg, lean body mass) should be considered in future study and when implementing tests.

Validity of Self-Reported Physical Fitness and Body Mass Index in a Military Population

Many epidemiological studies rely on valid physical fitness data. The purpose of this investigation was to assess the validity of self-reported Army Physical Fitness Test (APFT) data and determine whether men and women recall APFT performance differently. U.S. Army soldiers (N = 1,047) completed a survey, including questions on height, weight, and most recent APFT performance. Height, weight, and APFT performance were also obtained from unit records. The mean ± SDs for unit and self-reported push-up repetitions were 63.5 ± 13.1 and 66.3 ± 14.0 for men and 37.7 ± 12.8 and 40.2 ± 12.8 for women, respectively. The mean ± SD for unit- and self-reported sit-up repetitions were 66.3 ± 11.4 and 68.1 ± 12.1 for men and 64.2 ± 13.6 and 66.5 ± 12.9 for women, respectively. The mean ± SD unit- and self-reported 2-mile run times were 15.2 ± 1.8 and 14.9 ± 1.6 minutes for men, and 18.0 ± 2.9 and 17.4 ± 1.9 minutes for women, respectively. Unit- and self-reported body mass indices (BMIs) (calculated by height and weight) were 26.4 ± 3.4 and 26.3 ± 3.6 for men and 24.6 ± 2.8 and 24.2 ± 3.3 for women. Correlations between unit- and self-reported scores for push-ups, sit-ups, 2-mile run, height, weight, and BMI were 0.82, 0.78, 0.85, 0.87, 0.97, and 0.88 for men and 0.86, 0.84, 0.87, 0.78, 0.98, and 0.78 for women, respectively. On average, men and women slightly overreported performance on the APFT and overestimated height, resulting in underestimated BMI. There was no difference in recall ability between men and women (p > 0.05). The very good to excellent correlations (r = 0.78-0.98) between unit- and self-reported scores indicate that self-reported data are valid for capturing physical fitness performance in this population.

Cold thermoregulatory responses following exertional fatigue

Participants in prolonged, physically demanding cold-weather activities are at risk for a condition called "thermoregulatory fatigue". During cold exposure, the increased gradient favoring body heat loss to the environment is opposed by physiological responses and clothing and behavioral strategies that conserve body heat stores to defend body temperature. The primary human physiological responses elicited by cold exposure are shivering and peripheral vasoconstriction. Shivering increases thermogenesis and replaces body heat losses, while peripheral vasoconstriction improves thermal insulation of the body and retards the rate of heat loss. A body of scientific literature supports the concept that prolonged and/or repeated cold exposure, fatigue induced by sustained physical exertion, or both together, can impair the shivering and vasoconstrictor responses to cold ("thermoregulatory fatigue"). The mechanisms accounting for this thermoregulatory impairment are not clear, but there is evidence to suggest that changes in central thermoregulatory control or peripheral sympathetic responsiveness to cold lead to thermoregulatory fatigue and increased susceptibility to hypothermia.

Thermal response to running across the Sahara desert: data for three men

BACKGROUND

There are limited data concerning the physiological responses to long-duration exercise collected under field conditions, and less data under harsh environmental conditions. This paper describes select environmental conditions and physiological responses of three runners attempting to run across the entire Sahara desert over a 111-d period.

METHODS

The runners started in Saint-Louis, Senegal, and we collected data on 2 d at the start of the expedition. Core temperature was measured via telemetry pill (Tpill), heart rate via Polar monitor, and metabolic rate (M) was estimated from two equations. The Pandolf equation uses movement speed and grade while Berglund's equation predicts M from heart rate and dry-bulb temperature. Data are presented as mean +/- SD (range).

RESULTS

The runners intermittently ran 8.0 km x h(-1) over 6 h during Night (warm-humid) conditions and 6.9 km x h(-1) over 7 h 40 min during Day (hot-dry) desert conditions. Mean Tpill was similar for both days (37.8 +/- 10.34 vs. 37.82 +/- 0.50 degrees C) while range was greater during the day (Day: 36.69-38.91 vs. Night: 37.11-38.48 degrees C). Heart rate was 128 +/- 16 (72-156) and 119 +/- 17 (75-147) bpm for Night and Day, respectively. Mmean was 299 +/- 66 (65-418) W x m(-2) and 364 +/- 117 (58-542) W x m(-2) during Night and 239 +/- 60 (67-356) and 244 +/- 139 (54-464) W x m(-2) during Day, estimated by Berglund and Pandolf, respectively.

CONCLUSIONS

During Day, the athletes ran slower than during Night, though Tpill was similar, indicative of the greater environmental strain. Mean predicted M was similar between equations, though maximum and minimal values were more extreme and rate-of-change dynamics faster according to Pandolf's equation.

Responses to mild cold stress are predicted by different individual characteristics in young and older subjects

Older individuals' ability to maintain core temperature during cold stress is impaired; however, the relative importance of individual characteristics that influence this response are unknown. The purpose of this study was to determine the relative influence of individual characteristics on core temperature and tissue insulation (I(t)) during mild cold stress. Forty-two young (23 +/- 1 yr, range 18-30 yr) and 46 older (71 +/- 1 yr, range 65-89 yr) subjects, varying widely in muscularity, adiposity, and body size, underwent a transient cooling protocol during which esophageal temperature (T(es)) was measured continuously and I(t) was calculated using standard equations. Multiple-regression analyses were performed to determine predictors of T(es) and I(t), and standardized regression coefficients were analyzed to determine the relative influence of each predictor. Candidate predictors included age, sex, weight, body surface area, body surface area-to-mass ratio, sum of skinfolds, percent fat, appendicular skeletal muscle mass, and thyroid hormone concentrations (triiodothyronine, thyronine). The sum of skinfolds explained 67% (P < 0.01) of the T(es) variance in young subjects vs. 2% (P = 0.30) in older subjects. Conversely, appendicular skeletal muscle mass explained a greater portion of the variance in older subjects for both T(es) (older: 28%, P < 0.01; young: 8%, not significant) and I(t) (older: 46%, P < 0.01; young: 17%, P < 0.01). The T(es) residual variance was considerably larger in older subjects (59-72% vs. 14-42% in young subjects), possibly due to varying rates of physiological aging. These results suggest that the relative influence of individual characteristics changes with aging.

Incidence of adverse reactions from 23,000 exposures to simulated terrestrial altitudes up to 8900 m

INTRODUCTION

Adverse reactions during hypobaric chamber operations result from changes in barometric pressure per se and to the related reductions in the partial pressure of inspired oxygen. Previous studies have indicated that an adverse reaction may occur in approximately 6% of exposures in chambers used for flight training. The purpose of this study was to determine the rate of adverse reactions in a chamber used exclusively for terrestrial altitude research studies.

METHODS

Data for incidence of ear block, sinus block, toothache, and other adverse reactions were analyzed using a master history file that contained information such as annual and total number of studies and human exposures, and onset and outcome of adverse reactions. Incidence for a given time period was calculated as (# of reactions x 100)/(# of exposures).

RESULTS

In 33 yr, there have been 23,656 human exposures and 296 adverse reactions. The overall incidence was 1.25 reactions per 100 exposures (0.72 for research volunteers and 0.53 for staff). The majority (75% of all reactions) were ear blocks (0.93 reactions per 100 exposures). Staff members were more likely than research volunteers to have more than one reaction.

DISCUSSION

The incidence of 1.25 reactions per 100 exposures for our chamber is considerably lower than that reported in the literature. This is due primarily to our use of lower altitudes and slower rates of ascent and descent compared with other facilities whose emphasis is on aircraft flight training.

Epidemiology of U.S. Army cold weather injuries, 1980-1999

BACKGROUND

Cold weather injuries (CWI) are of great military concern due to their wide-ranging impact on military readiness. Previous short-term studies have identified CWI to be more prevalent in African-Americans, infantrymen, and lower-ranking soldiers. The purpose of this cross-sectional study was to determine the occurrence of CWI hospitalizations in the U.S. Army from 1980 to 1999, and to identify possible trends, high-risk groups and/or activities.

METHODS

The U.S. Army Research Institute of Environmental Medicine Total Army Injury and Health Outcomes Database was searched for hospitalizations with ICD-9-CM codes for frostbite, hypothermia, immersion foot, chilblains, and other. Information concerning each soldier included: gender, age, ethnicity, rank, occupation, type of injury, home of record, duty station, principle diagnosis, trauma code, and cause of injury. Data was available on the demographic composition of the Army, by year, and was used as the denominator when calculating the frequency of occurrence.

RESULTS

During the study period there were 2143 hospitalizations due to CWI. African-American men and women were injured approximately 4 times and 2.2 times as often as their Caucasian counterparts, respectively. Trauma and cause of injury codes indicate that about 80% of all CWI hospitalizations result on-duty and during organized training. The yearly rate of CWI hospitalization has declined from 38.2/100,000 in 1985 to 0.2/100,000 in 1999.

CONCLUSIONS

Our data are consistent with previous research concerning the increased rate of CWI among African-Americans though further investigation appears warranted. The occurrence of most CWI during on-duty training suggests preventability. The decline in the overall rate of CWI hospitalizations is multifactorial.

Pituitary-adrenal and pituitary-thyroid hormone responses during exercise-cold exposure after 7 days of exhaustive exercise

BACKGROUND

After several days of exhaustive exercise in mild-warm environments, cutaneous vasoconstrictor responses to cold exposure are less effective in conserving body heat than in the rested condition. Hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes hormones could mediate this response since they may affect vasoconstriction. The effects of exertional fatigue on pituitary-adrenal hormones and thyroid hormone responses to exercise-cold stress are unknown.

HYPOTHESIS

We hypothesized that 7 consecutive days of exercise would decrease adrenocorticotropin (ACTH) and cortisol, while elevating thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) and that these hormones would be related to a blunted vasoconstrictor response to cold.

METHODS

Nine male volunteers walked, completely wetted, for up to 6 h in 5 degrees C air, when rested (day 0, control) and after 7 consecutive days (day 7) of exhaustive exercise (4 h each day of mixed aerobic and anaerobic activities in thermoneutral conditions). Blood was sampled on day 0 and day 7 at baseline (0700 hours), and before and immediately after cold exposure.

RESULTS

At 0700 hours, ACTH and cortisol were elevated (p < 0.05) after 7 d of exercise, compared with control conditions. Following exercise-cold exposure, cortisol, T3, and T4 increased (p < 0.05) similarly on both day 0 and day 7. ACTH and TSH did not increase as a result of exercise-cold exposure on either day.

CONCLUSIONS

These data indicate that 7 d of exercise elevates basal (0700 hours) pituitary-adrenal stress hormones (ACTH, cortisol). However, 7 d of exercise did not modify adrenal or thyroid hormone responses, relative to the day 0 cold exposure, suggesting that they are not responsible for the blunted vasoconstriction during exercise-cold exposure following 7 consecutive days of exercise.

Physiological responses to cold exposure in men: a disabled submarine study

A disabled submarine (DISSUB) lacking power and/or environmental control will become cold, and the ambient air may become hypercapnic and hypoxic. This study examined if the combination of hypoxia, hypercapnia, and cold exposure would adversely affect thermoregulatory responses to acute cold exposure in survivors awaiting rescue. Seven male submariners (33 +/- 6 yrs) completed a series of cold-air tests (CAT) that consisted of 20-min at T(air) = 22 degrees C, followed by a linear decline (1 degrees C x min(-1)) in T(air) to 12 degrees C, which was then held constant for an additional 150-min. CAT were performed under normoxic, normocapnic conditions (D0), acute hypoxia (D1, 16.75% O2), after 4 days of chronic hypoxia, hypercapnia and cold (D5, 16.75% O2, 2.5% CO2, 4 degrees C), and hypoxia-only again (D8, 16.75% O2). The deltaTsk during CAT was larger (P < 0.05) on D0 (-5.2 degrees C), vs. D1 (-4.8 degrees C), D5 (-4.5 degrees C), and D8 (-4.4 degrees C). The change (relative to 0-min) in metabolic heat production (deltaM) at 20-min of CAT was lower (P < 0.05) on D1, D5, and D8, vs. D0, with no differences between D1, D5 and D8. DeltaM was not different among trials at any time point after 20-min. The mean body temperature threshold for the onset of shivering was lower on D1 (35.08 degrees C), D5 (34.85 degrees C), and D8 (34.69 degrees C), compared to D0 (36.01 degrees C). Changes in heat storage did not differ among trials and rectal temperature was not different in D0 vs. D1, D5, and D8. Thus, mild hypoxia (16.75% F1O2) impairs vasoconstrictor and initial shivering responses, but the addition of elevated F1CO2 and cold had no further effect. These thermoregulatory effector changes do not increase the risk for hypothermia in DISSUB survivors who are adequately clothed.

Lactic acid accumulation in cardiac patients performing circuit weight training: implications for exercise prescription

OBJECTIVE

Because blood lactic acid (LA) levels may be important in prescribing exercise for cardiac patients, this study documented the LA response to four different circuit weight training (CWT) protocols and compared these responses to both maximal treadmill and LA threshold values.

DESIGN

Intervention study following a crossover trial design.

SETTING

A phase III community-based setting.

PATIENTS

All subjects had documented cardiac disease and were volunteers.

INTERVENTIONS

We used 40% and 60% of the one-repetition maximum (1-RM) for six exercises and 30 or 60sec of rest between each station, resulting in four protocols, performed in random order. A discontinuous treadmill test was conducted, and the LA threshold was determined.

MAIN OUTCOME MEASURE

The main dependent variable was LA after each CWT protocol.

RESULTS

No signs or symptoms suggestive of cardiovascular distress during any of the four CWT protocols were reported. A repeated-measures analysis of variance showed that the LA threshold value was significantly less than all four CWT protocols (p < .05). The CWT responses were also compared with the traditional LA threshold value of 4.0mmol/L, and both 60% protocols were significantly elevated (p < .05).

CONCLUSION

Because no positive signs or symptoms were reported, we recommend starting stable cardiac patients on a CWT program with an initial load between 40% and 60% 1-RM and allowing at least 60sec of rest between exercises.

Circuit weight training in cardiac patients: determining optimal workloads for safety and energy expenditure

BACKGROUND

While most studies suggest circuit weight training (CWT) to be safe in cardiac rehabilitation populations, few investigators have controlled variables known to impact CWT intensity. Therefore, the purposes of this study were to determine the energy cost and evaluate safety of cardiac patients while varying rest interval duration and lifting load in a CWT format.

METHODS

Nine male subjects with documented coronary artery disease had maximal oxygen uptake (VO2max), one-repetition maximum (1-RM), and body composition tested. In random order and on separate days, 4 CWT sessions using either 40% or 60% of the 1-RM, and either 30 or 60 seconds of rest between stations were completed. Energy cost, heart rate (HR), blood pressure (BP), and rate-pressure product (RPP) were measured. Data were analyzed with a repeated measures analysis of variance, and Tukey's post-hoc test was performed when significant results were found. The alpha level was set at < .05.

RESULTS

Subjects exercised at 25% to 32% of VO2max (58%-67% of HRmax) during CWT. The HR and RPP responses were lower during all CWT protocols than at 85% of the treadmill VO2max. No subject displayed any ST-segment depression or angina during CWT. The 40%-60-second protocol had an energy cost (2.98 kcal/min) that was lower (P < .05) than the other protocols (3.48-3.81 kcal/min). Increasing the lifting load resulted in increases (P < .05) in energy cost, and decreasing the rest interval increased energy cost only during the 40% 1-RM protocols.

CONCLUSIONS

Results indicate that CWT protocols of varied intensity are safe for cardiac patients when compared to treadmill exercise, and changes in rest interval duration and load can impact the energy cost.