Search Results

You are looking at 1 - 10 of 10 items for

  • Author: Kevin C. Miller x
Clear All Modify Search
Restricted access

Megan L. Keen and Kevin C. Miller

Clinical Scenario:

Exercise performed in hot and humid environments increases core body temperature (TC). If TC exceeds 40.5°C for prolonged periods of time, exertional heat stroke (EHS) may occur. EHS is a leading cause of sudden death in athletes. Mortality and morbidity increase the longer the patient’s TC remains above 40.5°C; thus, it is imperative to initiate cooling as quickly as possible. Acceptable cooling rates in EHS situations are 0.08–0.15°C/min, while ideal cooling rates are above 0.16°C/min. Cooling vests are popular alternatives for cooling hyperthermic adults. Most vests cover the anterior and posterior torso and have varying numbers of pouches for phase-change materials (eg, gel packs); some vests only use circulating water to cool. While cooling vests offer several advantages (eg, portability), studies demonstrating their effectiveness at rapidly reducing TC in EHS scenarios are limited.

Clinical Question:

Are TC cooling rates acceptable (ie, >0.08°C/min) when hyperthermic humans are treated with cooling vests postexercise?

Summary of Findings:

No significant differences in TC cooling rates occurred between cooling vests and no cooling vests. Cooling rates across all studies were ≤0.053°C/min.

Clinical Bottom Line:

Cooling vests do not provide acceptable cooling rates of hyperthermic humans postexercise and should not be used to treat EHS. Instead, EHS patients should be treated with cold-water immersion within 30 min of collapse to avoid central nervous system dysfunction and organ failure.

Strength of Recommendation:

Strong evidence (eg, level 2 studies with PEDro scores ≥5) suggests that cooling vests do not reduce TC quickly and thus should not be used in EHS scenarios.

Open access

Kayla E. Boehm and Kevin C. Miller

Clinical Scenario: Exertional heat stroke (EHS) is a medical emergency characterized by body core temperatures >40.5°C and central nervous system dysfunction. An EHS diagnosis should be immediately followed by cold-water immersion (CWI). Ideally, EHS victims cool at a rate >0.15°C/min until their temperature reaches 38.9°C. While generally accepted, these EHS treatment recommendations often stem from research that examined only males. Since gender differences exist in anthropomorphics (eg, body surface area, lean body mass) and anthropomorphics impact CWI cooling rates, it is possible that CWI cooling rates may differ between genders. Clinical Question: Do CWI rectal temperature (T rec) cooling rates differ between hyperthermic males and females? Summary of Findings: The average T rec cooling rate across all examined studies for males and females was 0.18 (0.05) and 0.24 (0.03)°C/min, respectively. Hyperthermic females cooled ∼33% faster than males. Clinical Bottom Line: Hyperthermic females cooled faster than males, most likely because of higher body surface area to mass ratios and less lean body mass. Regardless of gender, CWI is highly effective at lowering T rec. Clinicians must be able to treat all EHS victims, regardless of gender, with CWI, given its high survival rate when implemented appropriately. Strength of Recommendation: Moderate evidence (2 level 3 studies) suggests that females cool faster than males when treated with CWI following severe hyperthermia. Despite gender differences, cooling rates exceeded cooling rate recommendations for EHS victims (ie, 0.15°C/min).

Restricted access

Tyler T. Truxton and Kevin C. Miller

Clinical Scenario:

Exertional heat stroke (EHS) is a medical emergency which, if left untreated, can result in death. The standard of care for EHS patients includes confirmation of hyperthermia via rectal temperature (Trec) and then immediate cold-water immersion (CWI). While CWI is the fastest way to reduce Trec, it may be difficult to lower and maintain water bath temperature in the recommended ranges (1.7°C–15°C [35°F–59°F]) because of limited access to ice and/or the bath being exposed to high ambient temperatures for long periods of time. Determining if Trec cooling rates are acceptable (ie, >0.08°C/min) when significantly hyperthermic humans are immersed in temperate water (ie, ≥20°C [68°F]) has applications for how EHS patients are treated in the field.

Clinical Question:

Are Trec cooling rates acceptable (≥0.08°C/min) when significantly hyperthermic humans are immersed in temperate water?

Summary of Findings:

Trec cooling rates of hyperthermic humans immersed in temperate water (≥20°C [68°F]) ranged from 0.06°C/min to 0.19°C/min. The average Trec cooling rate for all examined studies was 0.11±0.06°C/min.

Clinical Bottom Line:

Temperature water immersion (TWI) provides acceptable (ie, >0.08°C/min) Trec cooling rates for hyperthermic humans post-exercise. However, CWI cooling rates are higher and should be used if feasible (eg, access to ice, shaded treatment areas).

Strength of Recommendation:

The majority of evidence (eg, Level 2 studies with PEDro scores ≥5) suggests TWI provides acceptable, though not ideal, Trec cooling. If possible, CWI should be used instead of TWI in EHS scenarios.

Open access

Timothy M. Wohlfert and Kevin C. Miller

Clinical Scenario: Exertional heat stroke (EHS) is a potentially deadly heat illness and poses a significant health risk to athletes; EHS survival rates are near 100% if properly recognized and treated. Whole-body cold water immersion (CWI) is the most effective method for lowering body core temperature. Precooling (PC) with CWI before exercise may prevent severe hyperthermia or EHS by increasing the body’s overall heat storage capacity. However, PC may also alter athletes’ perception of how hot they feel or how hard they are exercising. Consequently, they may be unable to accurately perceive their body core temperature or how hard they are working, which may predispose them to severe hyperthermia or EHS. Clinical Question: Does PC with whole-body CWI affect thermal sensation (TS) or rating of perceived exertion (RPE) during exercise in the heat? Summary of Key Findings: In 4 studies, RPE during exercise ranged from 12 (2.0) to 20 (3.0), with no clinically meaningful differences between PC and control trials. TS scores ranged from 2 (1.0) to 8 (0.5) in control trials and from 2 (1.0) to 7.5 (0.5) during PC trials. Clinical Bottom Line: PC did not cause clinically meaningful differences in RPE or TS during exercise. It is unlikely that PC would predispose athletes to EHS by altering perceptions of exercise intensity or body core temperature. Strength of Recommendation: None of the reviewed studies (all level-2 studies with Physiotherapy Evidence Database scores ≥ 5) suggest that PC with CWI influences RPE or TS in exercising males.

Restricted access

Donal Murray, Kevin C. Miller and Jeffrey E. Edwards

Clinical Scenario:

Although exercise-associated muscle cramps (EAMC) are common in ultradistance runners and athletes in general, their etiology remains unclear. EAMC are painful, sudden, involuntary contractions of skeletal muscle occurring during or after exercise and are recognized by visible bulging or knotting of the whole, or part of, a muscle. Many clinicians believe EAMC occur after an imbalance in electrolyte concentrations, specifically serum sodium concentration ([Na+]s) and serum potassium concentration ([K+]s). Studies that have established a link between EAMC occurrence and serum electrolyte concentrations after an athletic event are unhelpful.

Focused Clinical Question:

Are [Na+]s and [K+]s different in athletes who experience EAMC than noncrampers?

Restricted access

Kevin C. Miller, Kenneth L. Knight, Steven R. Wilding and Marcus B. Stone

Context:

Electrically induced muscle cramps (EIMC) do not last long enough to study many cramp treatments. Increasing stimulation frequency lengthens cramp duration; it is unknown which frequency elicits the longest EIMC.

Objective:

To determine which stimulation frequency elicits the longest EIMC and whether cramp duration and stimulation frequency are correlated.

Design:

Randomized, crossover.

Setting:

Laboratory.

Participants:

20 participants (12 male, 8 female; age 20.7 ± 0.6 y; height 174.9 ± 1.9 cm; mass 76.6 ± 2.2 kg) with a self-reported history of muscle cramps in their lower extremities within the 6 mo before the study.

Interventions:

The dominant leg’s tibial nerve was percutaneously stimulated with 2-s-duration electrical stimuli trains starting at a frequency of 4 Hz. After 1 min of rest, stimulation frequency increased in 2-Hz increments until a cramp occurred in the flexor hallucis brevis. The stimulation frequency at which a cramp occurred was termed cramp threshold frequency (TF). Cramp duration was determined using strict clinical criteria (loss of hallux rigidity and return of hallux neutral). On the next 4 consecutive days, participants were stimulated at 5, 10, 15, or 20 Hz above TF, and cramp duration was reassessed.

Main Outcome Measures:

Cramp TF and duration.

Results:

Cramp TF was 16.9 ± 5.1 Hz. Cramp duration was longer at 15 and 20 Hz above TF (77.9 ± 37.6 s and 69.5 ± 36.9 s, respectively) than at TF (40.8 ± 34.0 s; P < .05). Cramp duration and TF were highly correlated (r = .90). Conclusions: Stimulating at 15 and 20 Hz above cramp TF produces the longest-lasting EIMC.

Restricted access

Jacqueline M. Del Giorno, Eric E. Hall, Kevin C. O’Leary, Walter R. Bixby and Paul C. Miller

The purpose of this study was to test the transient hypofrontality theory (Dietrich, 2003) by examining the influence of exercise intensity on executive control processes during and following submaximal exercise. Thirty participants (13 female) exercised for 30 min at ventilatory threshold (VT) or at 75% of VT. The Contingent Continuous Performance Task (CPT) and Wisconsin Card Sorting Test (WCST) were used as measures of executive control. They were administered before, during, immediately following, and 20 min after exercise. An increase in false alarms and unique errors (p ≤ .05) occurred during both conditions. False alarms for the CPT and total and perseverative errors for the WCST remained elevated immediately following exercise at VT, but not at exercise below VT (p ≤ .01). The decreased executive control function during exercise can be explained by the transient hypofrontality theory. Following VT, executive control performance remained poor possibly owing to an additional amount of time the brain needs to return to homeostasis following intense exercise.

Restricted access

Kayla E. Boehm, Blaine C. Long, Mitchell T. Millar and Kevin C. Miller

Effectiveness of Kinesiology Tex Tape (KTT) is conflicting, with some clinicians supporting and others refuting its effects. There is limited information on the psychological effects of KTT or whether its increased use has been influenced by professional athletes. The purpose of this study was to assess the physiological, psychological, and use of KTT. A descriptive survey on the use of KTT was performed with athletic trainers and other health care providers. Many reported that KTT benefited patients physiologically and psychologically. Those who thought KTT provided a physiological benefit indicated that they use it. Many indicated KTT benefited patients psychologically, without impacting them physiologically. In addition, clinicians indicated KTT use has been influenced by professional athletes.

Restricted access

Kevin C. Miller, Kenneth L. Knight and Richard B. Williams

Edited by Tricia Hubbard

Restricted access

Jodi L. Burrer, Pamela J. Hansen, Kevin C. Miller and Bryan Christensen