Rebecca M. Lopez

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses.

OBJECTIVE To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation. BACKGROUND Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes. RECOMMENDATIONS Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

Influence of Hydration on Physiological Function and Performance During Trail Running in the Heat

CONTEXT Authors of most field studies have not observed decrements in physiologic function and performance with increases in dehydration, although authors of well-controlled laboratory studies have consistently reported this relationship. Investigators in these field studies did not control exercise intensity, a known modulator of body core temperature. OBJECTIVE To directly examine the effect of moderate water deficit on the physiologic responses to various exercise intensities in a warm outdoor setting. DESIGN Semirandomized, crossover design. SETTING Field setting. PATIENTS OR OTHER PARTICIPANTS Seventeen distance runners (9 men, 8 women; age = 27 +/- 7 years, height = 171 +/- 9 cm, mass = 64.2 +/- 9.0 kg, body fat = 14.6% +/- 5.5%). INTERVENTION(S) Participants completed four 12-km runs (consisting of three 4-km loops) in the heat (average wet bulb globe temperature = 26.5 degrees C): (1) a hydrated, race trial (HYR), (2) a dehydrated, race trial (DYR), (3) a hydrated, submaximal trial (HYS), and (4) a dehydrated, submaximal trial (DYS). MAIN OUTCOME MEASURE(S) For DYR and DYS trials, dehydration was measured by body mass loss. In the submaximal trials, participants ran at a moderate pace that was matched by having them speed up or slow down based on pace feedback provided by researchers. Intestinal temperature was recorded using ingestible thermistors, and participants wore heart rate monitors to measure heart rate. RESULTS Body mass loss in relation to a 3-day baseline was greater for the DYR (-4.30% +/- 1.25%) and DYS trials (-4.59% +/- 1.32%) than for the HYR (-2.05% +/- 1.09%) and HYS (-2.0% +/- 1.24%) trials postrun (P < .001). Participants ran faster for the HYR (53.15 +/- 6.05 minutes) than for the DYR (55.7 +/- 7.45 minutes; P < .01), but speed was similar for HYS (59.57 +/- 5.31 minutes) and DYS (59.44 +/- 5.44 minutes; P > .05). Intestinal temperature immediately postrun was greater for DYR than for HYR (P < .05), the only significant difference. Intestinal temperature was greater for DYS than for HYS postloop 2, postrun, and at 10 and 20 minutes postrun (all: P < .001). Intestinal temperature and heart rate were 0.22 degrees C and 6 beats/min higher, respectively, for every additional 1% body mass loss during the DYS trial compared with the HYS trial. CONCLUSIONS A small decrement in hydration status impaired physiologic function and performance while trail running in the heat.

The American Football Uniform: Uncompensable Heat Stress and Hyperthermic Exhaustion

CONTEXT In hot environments, the American football uniform predisposes athletes to exertional heat exhaustion or exercise-induced hyperthermia at the threshold for heat stroke (rectal temperature [T(re)] > 39 degrees C). OBJECTIVE To evaluate the differential effects of 2 American football uniform configurations on exercise, thermal, cardiovascular, hematologic, and perceptual responses in a hot, humid environment. DESIGN Randomized controlled trial. SETTING Human Performance Laboratory. PATIENTS OR OTHER PARTICIPANTS Ten men with more than 3 years of competitive experience as football linemen (age = 23.8 +/- 4.3 years, height = 183.9 +/- 6.3 cm, mass = 117.41 +/- 12.59 kg, body fat = 30.1% +/- 5.5%). INTERVENTION(S) Participants completed 3 controlled exercise protocols consisting of repetitive box lifting (lifting, carrying, and depositing a 20.4-kg box at a rate of 10 lifts per minute for 10 minutes), seated recovery (10 minutes), and up to 60 minutes of treadmill walking. They wore one of the following: a partial uniform (PART) that included the National Football League (NFL) uniform without a helmet and shoulder pads; a full uniform (FULL) that included the full NFL uniform; or control clothing (CON) that included socks, sneakers, and shorts. Exercise, meals, and hydration status were controlled. MAIN OUTCOME MEASURE(S) We assessed sweat rate, T(re), heart rate, blood pressure, treadmill exercise time, perceptual measurements, plasma volume, plasma lactate, plasma glucose, plasma osmolality, body mass, and fat mass. RESULTS During 19 of 30 experiments, participants halted exercise as a result of volitional exhaustion. Mean sweat rate, T(re), heart rate, and treadmill exercise time during the CON condition were different from those measures during the PART (P range, .04-.001; d range, 0.42-0.92) and FULL (P range, .04-.003; d range, 1.04-1.17) conditions; no differences were detected for perceptual measurements, plasma volume, plasma lactate, plasma glucose, or plasma osmolality. Exhaustion occurred during the FULL and PART conditions at the same T(re) (39.2 degrees C). Systolic and diastolic blood pressures (n = 9) indicated that hypotension developed throughout exercise (all treatments). Compared with the PART condition, the FULL condition resulted in a faster rate of T(re) increase (P < .001, d = 0.79), decreased treadmill exercise time (P = .005, d = 0.48), and fewer completed exercise bouts. Interestingly, T(re) increase was correlated with lean body mass during the FULL condition (R(2) = 0.71, P = .005), and treadmill exercise time was correlated with total fat mass during the CON (R(2) = 0.90, P < .001) and PART (R(2) = 0.69, P = .005) conditions. CONCLUSIONS The FULL and PART conditions resulted in greater physiologic strain than the CON condition. These findings indicated that critical internal temperature and hypotension were concurrent with exhaustion during uncompensable (FULL) or nearly uncompensable (PART) heat stress and that anthropomorphic characteristics influenced heat storage and exercise time to exhaustion.

The effects of resistance training on endurance distance running performance among highly trained runners: a systematic review.

The current perception among highly competitive endurance runners is that concurrent resistance and endurance training (CT) will improve running performance despite the limited research in this area. The purpose of this review was to search the body of scientific literature for original research addressing the effects of CT on distance running performance in highly competitive endurance runners. Specific key words (including running, strength training, performance, and endurance) were used to search relevant databases through April 2007 for literature related to CT. Original research was reviewed using the Physiotherapy Evidence Database (PEDro) scale. Five studies met inclusion criteria: highly trained runners (>or= 30 mile x wk(-1) or >or= 5 d x wk(-1)), CT intervention for a period >or= 6 weeks, performance distance between 3K and 42.2K, and a PEDro scale score >or= 5 (out of 10). Exclusion criteria were prepubertal children and elderly populations. Four of the five studies employed sport-specific, explosive resistance training, whereas one study used traditional heavy weight resistance training. Two of the five studies measured 2.9% improved performance (3K and 5K), and all five studies measured 4.6% improved running economy (RE; range = 3-8.1%). After critically reviewing the literature for the impact of CT on high-level runners, we conclude that resistance training likely has a positive effect on endurance running performance or RE. The short duration and wide range of exercises implemented are of concern, but coaches should not hesitate to implement a well-planned, periodized CT program for their endurance runners.

Comparison of Body Cooling Methods on Physiological and Perceptual Measures of Mildly Hyperthermic Athletes

DeMartini, JK, Ranalli, GF, Casa, DJ, Lopez, RM, Ganio, MS, Stearns, RL, McDermott, BP, Armstrong, LE, and Maresh, CM. Comparison of body cooling methods on physiological and perceptual measures of mildly hyperthermic athletes. J Strength Cond Res 25(8): 2065-2074, 2011—Hyperthermia is common among athletes and in a variety of environments. The purpose of this study was to evaluate the effectiveness of cooling methods on core body temperature, heart rate (HR), and perceptual readings in individuals after exercise. Sixteen subjects (age: 24 ± 6 years, height: 182 ± 7 cm, weight: 74.03 ± 9.17 kg, and body fat: 17.08 ± 6.23%) completed 10 exercise sessions in warm conditions (WBGT: 26.64 ± 4.71°C) followed by body cooling by 10 different methods. Cooling methods included cold water immersion (CWI), shade, Port-a-Cool® (FAN), Emergency Cold Containment System® (ECCS), Rehab. Hood® (HOOD), Game Ready Active Cooling Vest™ (GRV), Nike Ice Vest™ (NIV), ice buckets (IBs), and ice towels (IT). These cooling modes were compared with a control (SUN). Rectal temperature (Tre), HR, thermal sensation, thirst sensation, and a 56-question Environmental Symptoms Questionnaire (ESQ) were used to assess physiological and perceptual data. Average Tre after exercise across all trials was 38.73 ± 0.12°C. After 10 minutes of cooling, CWI (−0.65 ± 0.29°C), ECCS (−0.68 ± 0.24°C), and IB (−0.74 ± 0.34°C) had significantly (p < 0.006) greater decreases in Tre compared with that in SUN (−0.42 ± 0.15°C). The HR after 10 minutes of cooling was significantly (p < 0.006) lower for CWI (82 ± 15 b·min−1), ECCS (87 ± 14 b·min−1), and IT (84 ± 15 b·min−1) when compared with SUN (101 ± 15 b·min−1). The thermal sensation between modalities was all significantly (p < 0.006) lower (CWI: 1.5 ± 0.5; Fan: 3.0 ± 1.0; ECCS: 4.5 ± 1.0; Hood: 4.5 ± 0.5; GRV: 4.0 ± 0.5; NIV: 4.5 ± 1.0; IB: 4.0 ± 1.0; IT: 3.0 ± 1.0) when compared with SUN (5.5 ± 0.5), except for Shade (5.0 ± 1.0). There were no significant differences (p > 0.006) in thirst sensation between modalities. The ESQ scores were significantly (p < 0.006) lower for CWI (1 ± 6), Fan (4 ± 5), and IT (3 ± 8) compared with that for SUN (13 ± 12). In conclusion, when athletes experience mild hyperthermia, CWI, ECCS, and IB resulted in a significantly greater decrease in Tre. These cooling strategies are recommended to decrease Tre during a brief recovery period between exercise bouts.

Active dehydration impairs upper and lower body anaerobic muscular power

We examined the effects of active dehydration by exercise in a hot, humid environment on anaerobic muscular power using a test-retest (euhydrated and dehydrated) design. Seven subjects (age, 27.1 ± 4.6 years; mass, 86.4 ± 9.5 kg) performed upper and lower body Wingate anaerobic tests prior to and after a 1.5-hour recovery from a heat stress trial of treadmill exercise in a hot, humid environment (33.1 ± 3.1oC = 55.1 ± 8.9% relative humidity) until a 3.1 ± 0.3% body mass loss was achieved. Dehydration was confirmed by a significant body mass loss (P < 0.001), urine color increase (P = 0.004), and urine specific gravity increase (P = 0.041). Motivation ratings were not significantly different (P = 0.059), and fatigue severity was significantly (P = 0.009) increased 70% in the dehydrated compared to the euhydrated condition. Compared to the euhydrated condition, the dehydrated condition mean power was significantly (P = 0.014) decreased 7.17% in the upper body and 19.20% in the lower body. Compared to the euhydrated condition, the dehydrated condition peak power was significantly (P = 0.013) decreased 14.48% in the upper body and 18.36% in the lower body. No significant differences between the euhydrated and dehydrated conditions were found for decrease in power output (P = 0.219, power = 0.213). Our findings suggest that dehydration of 2.9% body mass decreases the ability to generate upper and lower body anaerobic power. Coaches and athletes must understand that sports performance requiring anaerobic strength and power can be impaired by inadequate hydration and may contribute to increased susceptibility to musculoskeletal injury.

Examining the influence of hydration status on physiological responses and running speed during trail running in the heat with controlled exercise intensity.

Lopez, RM, Casa, DJ, Jensen, KA, DeMartini, JK, Pagnotta, KD, Ruiz, RC, Roti, MW, Stearns, RL, Armstrong, LE, and Maresh, CM. Examining the influence of hydration status on physiological responses and running speed during trail running in the heat with controlled exercise intensity. J Strength Cond Res 25(11): 2944–2954, 2011—The purpose of this study was to determine the effects of dehydration at a controlled relative intensity on physiological responses and trail running speed. Using a randomized, controlled crossover design in a field setting, 14 male and female competitive, endurance runners aged 30 ± 10.4 years completed 2 (hydrated [HY] and dehydrated [DHY]) submaximal trail runs in a warm environment. For each trial, the subjects ran 3 laps (4 km per lap) on trails with 4-minute rests between laps. The DHY were fluid restricted 22 hours before the trial and during the run. The HY arrived euhydrated and were given water during rest breaks. The subjects ran at a moderate pace matched between trials by providing pacing feedback via heart rate (HR) throughout the second trial. Gastrointestinal temperature (TGI), HR, running time, and ratings of perceived exertion (RPE) were monitored. Percent body mass (BM) losses were significantly greater for DHY pretrial (−1.65 ± 1.34%) than for HY (−0.03 ± 1.28%; p < 0.001). Posttrial, DHY BM losses (−3.64 ± 1.33%) were higher than those for HY (−1.38 ± 1.43%; p < 0.001). A significant main effect of TGI (p = 0.009) was found with DHY having higher TGI postrun (DHY: 39.09 ± 0.45°C, HY: 38.71 ± 0.45°C; p = 0.030), 10 minutes post (DHY: 38.85 ± 0.48°C, HY: 38.46 ± 0.46°C; p = 0.009) and 30 minutes post (DHY: 38.18 ± 0.41°C, HY: 37.60 ± 0.25°C; p = 0.000). The DHY had slower run times after lap 2 (p = 0.019) and lap 3 (p = 0.025). The DHY subjects completed the 12-km run 99 seconds slower than the HY (p = 0.027) subjects did. The RPE in DHY was slightly higher than that in HY immediately postrun (p = 0.055). Controlling relative intensity in hypohydrated runners resulted in slower run times, greater perceived effort, and elevated TGI, which is clinically meaningful for athletes using HR as a gauge for exercise effort and performance.

Thermoregulatory Influence of a Cooling Vest on Hyperthermic Athletes

CONTEXT Athletic trainers must have sound evidence for the best practices in treating and preventing heat-related emergencies and potentially catastrophic events. OBJECTIVE To examine the effectiveness of a superficial cooling vest on core body temperature (T(c)) and skin temperature (T(sk)) in hypohydrated hyperthermic male participants. DESIGN A randomized control design with 2 experimental groups. SETTING Participants exercised by completing the heat-stress trial in a hot, humid environment (ambient temperature = 33.1 +/- 3.1 degrees C, relative humidity = 55.1 +/- 8.9%, wind speed = 2.1 +/- 1.1 km/hr) until a T(c) of 38.7 +/- 0.3 degrees C and a body mass loss of 3.27 +/- 0.1% were achieved. PATIENTS OR OTHER PARTICIPANTS Ten healthy males (age = 25.6 +/- 1.6 years, mass = 80.3 +/- 13.7 kg). INTERVENTION(S) Recovery in a thermoneutral environment wearing a cooling vest or without wearing a cooling vest until T(c) returned to baseline. MAIN OUTCOME MEASURE(S) Rectal T(c), arm T(sk), time to return to baseline T(c), and cooling rate. RESULTS During the heat-stress trial, T(c) significantly increased (3.6%) and, at 30 minutes of recovery, T(c) had decreased significantly (2.6%) for both groups. Although not significant, the time for return to baseline T(c) was 22.6% faster for the vest group (43.8 +/- 15.1 minutes) than for the no-vest group (56.6 +/- 18.0 minutes), and the cooling rate for the vest group (0.0298 +/- 0.0072 degrees C/min) was not significantly different from the cooling rate for the no-vest group (0.0280 +/- 0.0074 degrees C/min). The T(sk) during recovery was significantly higher (2.1%) in the vest group than in the no-vest group and was significantly lower (7.1%) at 30 minutes than at 0 minutes for both groups. CONCLUSIONS We do not recommend using the cooling vest to rapidly reduce elevated T(c). Ice-water immersion should remain the standard of care for rapidly cooling severely hyperthermic individuals.

Perceptual Responses While Wearing an American Football Uniform in the Heat

CONTEXT The protective equipment worn during American football has been shown to increase thermal strain; however, the perception of this increased heat has not been examined. OBJECTIVE To evaluate perceptual responses of American football players while wearing different uniforms during exercise in the heat and to evaluate how these responses may be used to monitor athlete safety. DESIGN Randomized controlled trial. SETTING Human Performance Laboratory. PATIENTS OR OTHER PARTICIPANTS Ten men with more than 3 years of competitive experience as football linemen (age = 23.8 +/- 1.3 years, height = 183.9 +/- 1.8 cm, mass = 117.4 +/- 3.5 kg, body fat = 30.1% +/- 1.7%) participated. INTERVENTION(S) On 3 occasions in hot, humid (33 degrees C, 48%-49% relative humidity) environmental conditions, participants completed 10 minutes of strenuous repetitive box lifting (RBL), 10 minutes of seated rest, and up to 60 minutes of treadmill walking. At each trial, they wore a different uniform condition: control (CON) clothing comprising shorts, socks, and sneakers; partial (PART) National Football League (NFL) uniform comprising the uniform without helmet or shoulder pads; or full (FULL) NFL uniform. Exercise, meals, and hydration status were controlled. MAIN OUTCOME MEASURE(S) Rectal temperature (T(re)), skin temperature (T(sk)), rating of perceived exertion (RPE), thermal perception (THM), perception of thirst (TST), and perception of muscle pain (MPN) were obtained for time points matched across trials. RESULTS Nineteen of the 30 trials ended before 60 minutes of treadmill walking as a result of participant exhaustion. Mean treadmill time was longer for the CON condition (51.7 +/- 13.4 minutes) than for the PART (43.1 +/- 15.6 minutes; t(9) = 3.092, P = .01) or the FULL (36.2 +/- 13.2 minutes; t(9) = 4.393, P = .002) conditions. Neck and forearm T(sk) increased between the initial time point and the end of exercise in the PART (33.6 +/- 0.9 degrees C and 35.0 +/- 0.6 degrees C, respectively; F(2,18) = 9.034, P < .001) and the FULL (33.4 +/- 0.9 degrees C and 35.2 +/- 0.6 degrees C, respectively; F(2,18) = 21.011, P = .002) conditions. Rate of T(re) rise was greater in the FULL (0.042 +/- 0.010 degrees C/min) than in the PART (0.034 +/- 0.006 degrees C/min) condition (F(2,27) = 10.69, P = .04). We found a relationship at the post-RBL and final time points between RPE and THM (r = 0.75, P < .001 and r = 0.59, P < .001, respectively), RPE and TST (r = 0.76, P < .001 and r = 0.61, P < .001, respectively), and RPE and MPN (r = 0.63, P < .001 and r = 0.64, P < .001, respectively). The RPE was greater at the end of exercise in the PART (17 +/- 2) and FULL (18 +/- 1) conditions than in the CON (15 +/- 3) condition (F(2,18) = 7.403, P = .005). CONCLUSIONS Although no differences in perceptual scales existed between the PART and FULL conditions, the T(sk) and rate of T(re) increase differed, indicating that football athletes find it difficult to perceptually rate exercise conditions as potentially dangerous hyperthermia develops. In addition, correlations between the perceptual scales further defined perceptual responses during exercise in the heat.

Plyometric Training Effects on Athletic Performance in Youth Soccer Athletes: A Systematic Review

Abstract Bedoya, AA, Miltenberger, MR, and Lopez, RM. Plyometric training effects on athletic performance in youth soccer athletes: A systematic review. J Strength Cond Res 29(8): 2351–2360, 2015—The purpose of this systematic review was to critically analyze the literature to determine the effectiveness of plyometric training on athletic performance in youth soccer athletes. A total of 7 studies were included in this review after meeting the following criteria: (a) used plyometric training programs to assess athletic performance, (b) subjects were soccer athletes aged preadolescent up to 17 years, and (c) were published from 2000 to January 2014. Study methods were assessed using the PEDro scale with scores ranging from 4 to 6. Results showed similarities and differences in methodologies and procedures among the included studies. Athletic performance consisting of kicking distance, speed, jumping ability, and agility significantly improved because of plyometric training interventions. The current evidence suggests that plyometric training should be completed 2 days per week for 8–10 weeks during soccer practice with a 72-hour rest period between plyometric training days. The initial number of foot contacts should be 50–60 per session and increase to no more than 80–120 foot contacts per session for this age group to prevent overuse injuries. A total of 3–4 plyometric training exercises should be performed 2–4 sets for 6–15 repetitions per training session. The evidence and the literature suggest that plyometric training for this age group should only be implemented using recommended safety guidelines such as those published by the Canadian Society for Exercise Physiology and the National Strength and Conditioning Association and under appropriate supervision by trained personnel.