Regional Surface Electromyography of the Vastus Lateralis During Strength and Power Exercises.

Neuromuscular activation during and chronic adaptation from exercise are innately linked and both can vary along a muscle's length. During high-force and high-speed exercise, intramuscular hypertrophy follows set patterns that provide the greatest biomechanical advantages. However, it is unknown if muscle activity as recorded by surface electromyography (sEMG) will follow these patterns. The purpose of the present study was to compare vastus lateralis intramuscular sEMG during the heavy squat (HS) and unloaded jump squat (JS) exercises. Ten subjects performed HS with 80% of maximum load and unloaded JS to parallel-depth, while intramuscular peak sEMG and mean sEMG were measured at 33% (proximal), 50% (middle), and 67% (distal) thigh length. Muscle activity was compared between regions and exercises using a 3 × 2 repeated measures ANOVA with Bonferoni post hoc corrections. Peak sEMG was greater proximally in JS than HS (p = 0.033), but similar in the middle and distal regions (p = 0.521, 0.594, respectively), whereas mean sEMG was similar between all regions (p = 0.150-0.979). In addition, a main effect was found in which peak and mean sEMG were greater proximally than the middle and distal regions (p = 0.001, 0.006). Muscle activity measured using sEMG displayed dissimilar patterns to previously observed regional hypertrophy. Specifically, although previous research found greater proximal hypertrophy in JS than HS, in the present study peak sEMG was greater in HS than JS. Furthermore, distally where HS elicited greater hypertrophy than JS, no differences in sEMG were present. Thus, regional sEMG appears not to be a viable tool for predicting differences in regional hypertrophy, most likely due to technological constraints and intramuscular differences in muscle structure.

Comparison of Two Fluid Replacement Protocols During a 20-km Trail Running Race in the Heat.

Lopez, RM, Casa, DJ, Jensen, K, Stearns, RL, DeMartini, JK, Pagnotta, KD, Roti, MW, Armstrong, LE, and Maresh, CM. Comparison of two fluid replacement protocols during a 20-km trail running race in the heat. J Strength Cond Res 30(9): 2609-2616, 2016-Proper hydration is imperative for athletes striving for peak performance and safety, however, the effectiveness of various fluid replacement strategies in the field setting is unknown. The purpose of this study was to investigate how two hydration protocols affect physiological responses and performance during a 20-km trail running race. A randomized, counter-balanced, crossover design was used in a field setting (mean ± SD: WBGT 28.3 ± 1.9° C). Well-trained male (n = 8) and female (n = 5) runners (39 ± 14 years; 175 ± 9 cm; 67.5 ± 11.1 kg; 13.4 ± 4.6% BF) completed two 20-km trail races (5 × 4-km loop) with different water hydration protocols: (a) ad libitum (AL) consumption and (b) individualized rehydration (IR). Data were analyzed using repeated measures ANOVA. Paired t-tests compared pre-race-post-race measures. Main outcome variables were race time, heart rate (HR), gastrointestinal temperature (TGI), fluid consumed, percent body mass loss (BML), and urine osmolality (Uosm). Race times between groups were similar. There was a significant condition × time interaction (p = 0.048) for HR, but TGI was similar between conditions. Subjects replaced 30 ± 14% of their water losses in AL and 64 ± 16% of their losses in IR (p < 0.001). Ad libitum trial experienced greater BML (-2.6 ± 0.5%) compared with IR (-1.3 ± 0.5%; p < 0.001). Pre-race to post-race Uosm differences existed between AL (-273 ± 146 mOsm) and IR (-145 ± 215 mOsm, p = 0.032). In IR, runners drank twice as much fluid than AL during the 20-km race, leading to > 2% BML in AL. Ad libitum drinking resulted in 1.3% greater BML over the 20-km race, which resulted in no thermoregulatory or performance differences from IR.

Maximum heat loss potential is lower in football linemen during an NCAA summer training camp because of lower self-generated air flow.

The purpose of this study was to compare the maximum potential for heat loss of football linemen (L) and non-linemen (NL) during a National Collegiate Athletic Association (NCAA) summer training camp. It was hypothesized that heat loss potential in L would be lower than NL because of differences in self-generated air flow during position-specific activities. Fourteen NCAA division 1 football players {7 L (mass: 126 ± 6 kg; body surface area [BSA]: 2.51 ± 0.19 m(2)) and 7 NL (mass: 88 ± 13 kg; BSA: 2.09 ± 0.18 m(2))} participated over 6 days in southern Florida (Tdb: 31.2 ± 1.6 °C, T(wb): 27.0 ± 0.7 °C, Tr: 38.4 ± 2.8° C). Simultaneous on-field measurements of self-generated air velocities (v(self)) and mean skin temperatures (Tsk) were performed throughout practice, which included 4 drill categories (special teams, wind sprints, individual drills, and team drills). The resultant net potential for heat loss through convection, radiation, and evaporation (H(total)) was calculated. Values for Tsk were similar between L and NL for all drills (L: 35.4 ± 0.8 °C; NL: 35.4 ± 0.4 °C; p = 0.92). However, v(self) was greater in NL during wind sprints, individual drills, and team drills (p ≤ 0.05). Consequently H(total) was significantly greater in NL for all drills except special teams (p ≤ 0.05). The mean estimated rate of oxygen consumption needed to exceed H(total) was 8.6 ± 1.3 ml · kg(-1) · min(-1) (2.5 ± 0.4 METs) for NL but only 5.6 ± 1.4 ml · kg(-1) · min(-1) (1.6 ± 0.4 METs) for L. A lower heat loss potential occurs in L because of the more static nature of their position-related activities and not because of differences in Tsk. The practical relevance of these findings is that potential interventions that increase convective and evaporative heat loss (i.e., mechanical fans) should specifically target L, particularly while they are participating in static on-field drills and during rest intervals.

Physical demands of National Collegiate Athletic Association Division I football players during preseason training in the heat.

The purpose of this study was to evaluate physical demands of football players during preseason practices in the heat. Furthermore, we sought to compare how physical demands differ between positions and playing status. Male National Collegiate Athletic Association Division 1 football players (n = 49) participated in 9 practice sessions (142 ± 16 minutes per session; wet bulb globe temperature (WBGT) 28.75 ± 2.11°C) over 8 days. Heart rate (HR) and global positioning system data were recorded throughout the entirety of each practice to determine the distance covered (DC), velocity (V), maximal HR (HRmax), and average HR (HRavg). The subjects were divided into 2 groups: linemen (L) (N = 25; age: 22 ± 1 years, weight: 126 ± 16 kg, height: 190 ± 4 cm,) vs. nonlinemen (NL) (N = 24; age: 21 ± 1 years, weight: 91 ± 11 kg, height: 183 ± 8 cm) and starters (S) (N = 17; age: 21 ± 1 years, weight: 118 ± 21 kg, height: 190 ± 7 cm) vs. nonstarters (NS) (N = 32; age: 20 ± 1 years, weight: 105 ± 22 kg, height: 185 ± 7 cm) for statistical analysis. The DC (3,532 ± 943 vs. 2,573 ± 489 m; p = 0.001) and HRmax (201 ± 9 vs. 194 ± 11 b·min(-1); p = 0.025) were significantly greater in NL compared with that in L. In addition, NL spent more time (p < 0.0001) and covered more distance (p = 0.002) at higher velocities than L did. Differences between S vs. NS were observed (p = 0.008, p = 0.031), with S obtaining higher velocities than NS did. Given the demands of their playing positions, NL were required to cover more distance at higher velocities, resulting in a greater HRmax than that of L. Therefore, it appears that L engage in more isometric work than NL do. In addition, the players exposed to similar practice demands provide similar work output during preseason practice sessions regardless of their playing status.

Comparison of body cooling methods on physiological and perceptual measures of mildly hyperthermic athletes.

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 (T(re)), HR, thermal sensation, thirst sensation, and a 56-question Environmental Symptoms Questionnaire (ESQ) were used to assess physiological and perceptual data. Average T(re) 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 T(re) 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 T(re). These cooling strategies are recommended to decrease T(re) during a brief recovery period between exercise bouts.

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

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 (T(GI)), 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 T(GI) (p = 0.009) was found with DHY having higher T(GI) 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 T(GI), which is clinically meaningful for athletes using HR as a gauge for exercise effort and performance.

National Athletic Trainers' Association Releases New Guidelines for Exertional Heat Illnesses: What School Nurses Need to Know.

Exertional heat illnesses (EHI) occur in various populations and settings. Within a school setting, there are student athletes who take part in physical activity where the risk of EHI is increased. The National Athletic Trainers' Association (NATA) released an updated position statement on EHI in September of 2015. This article is a summary of the position statement. The sports medicine team, including school nurses and athletic trainers, provides quality health care to these physically active individuals. Thus, it is important for school nurses to understand the prevention, recognition, and treatment of EHI.

Effectiveness of cold water immersion in the treatment of exertional heat stroke at the Falmouth Road Race.

PURPOSE: This study aimed to investigate the effectiveness (speed of cooling and survival rates) of cold water immersion (CWI) in the treatment of patients with exertional heat stroke (EHS). Secondly, this study aimed to compare cooling rates on the basis of gender, age, and initial rectal temperature (Tr). METHODS: Eighteen years of finish line medical tent patient records were obtained from the exertional heat illness treatment area at the Falmouth Road Race. Study participants included patients with EHS who were treated with CWI in the medical tent. The number of EHS cases was recorded for each year, and incidence was established on the basis of the number of finishers. Overall cooling rate and differences between initial Tr, age, and sex were evaluated. RESULTS: A total of 274 cases of EHS was observed over the 18 yr of collected data. A mean of 15.2 ± 13.0 EHS cases per year was recorded, with an overall incidence of 2.13 ± 1.62 EHS cases per 1000 finishers. The average initial Tr was 41.44°C ± 0.63°C, and the average cooling rate for patients with EHS was 0.22°C·min ± 0.11°C·min. CWI resulted in a 100% survival rate for all patients with EHS. No significant interactions between cooling rate and initial Tr (P = 0.778), sex (P = 0.89), or age (P = 0.70) were observed. CONCLUSIONS: CWI was found to effectively treat all cases of EHS observed in this study. CWI provided similar treatment outcomes in all patients, with no significant differences noted on the basis of initial Tr, age, or sex. On the basis of the 100% survival rate from EHS in this large cohort, it is recommended that immediate (on site) CWI be implemented for the treatment of EHS.

Bike and run pacing on downhill segments predict Ironman triathlon relative success.

OBJECTIVES: Determine if performance and physiological based pacing characteristics over the varied terrain of a triathlon predicted relative bike, run, and/or overall success. Poor self-regulation of intensity during long distance (Full Iron) triathlon can manifest in adverse discontinuities in performance. DESIGN: Observational study of a random sample of Ironman World Championship athletes. High performing and low performing groups were established upon race completion. METHODS: Participants wore global positioning system and heart rate enabled watches during the race. Percentage difference from pre-race disclosed goal pace (%off) and mean HR were calculated for nine segments of the bike and 11 segments of the run. Normalized graded running pace (accounting for changes in elevation) was computed via analysis software. Step-wise regression analyses identified segments predictive of relative success and HP and LP were compared at these segments to confirm importance. RESULTS: %Off of goal velocity during two downhill segments of the bike (HP: -6.8±3.2%, -14.2±2.6% versus LP: -1.2±4.2%, -5.1±11.5%; p<0.020) and %off from NGP during one downhill segment of the run (HP: 4.8±5.2% versus LP: 33.3±38.7%; p=0.033) significantly predicted relative performance. Also, HP displayed more consistency in mean HR (141±12 to 138±11 bpm) compared to LP (139±17 to 131±16 bpm; p=0.019) over the climb and descent from the turn-around point during the bike component. CONCLUSIONS: Athletes who maintained faster relative speeds on downhill segments, and who had smaller changes in HR between consecutive up and downhill segments were more successful relative to their goal times.

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.

Environmental conditions and the occurrence of exertional heat illnesses and exertional heat stroke at the Falmouth Road Race.

CONTEXT: The Falmouth Road Race is unique because of the environmental conditions and relatively short distance, which allow runners to maintain a high intensity for the duration of the event. Therefore, the occurrence of exertional heat illnesses (EHIs), especially exertional heat stroke (EHS), is 10 times higher than in other races. OBJECTIVE: To summarize the occurrence and relationship of EHI and environmental conditions at the Falmouth Road Race. DESIGN: Descriptive epidemiologic study. SETTING: An 11.3-km (7-mile) road race in Falmouth, Massachusetts. PATIENTS OR OTHER PARTICIPANTS: Runners who sustained an EHI while participating in the Falmouth Road Race. MAIN OUTCOME MEASURE(S): We obtained 18 years of medical records and environmental conditions from the Falmouth Road Race and documented the incidence of EHI, specifically EHS, as related to ambient temperature (Tamb), relative humidity, and heat index (HI). RESULTS: Average Tamb, relative humidity, and HI were 23.3 ± 2.5°C, 70 ± 16%, and 24 ± 3.5°C, respectively. Of the 393 total EHI cases observed, EHS accounted for 274 (70%). An average of 15.2 ± 13.0 EHS cases occurred each year; the incidence was 2.13 ± 1.62 cases per 1000 runners. Regression analysis revealed a relationship between the occurrence of both EHI and EHS and Tamb (R(2) = 0.71, P = .001, and R(2) = 0.65, P = .001, respectively) and HI (R(2) = 0.76, P < .001, and R(2) = 0.74, P < .001, respectively). Occurrences of EHS (24.2 ± 15.5 cases versus 9.3 ± 4.3 cases) and EHI (32.3 ± 16.3 versus 13.0 ± 4.9 cases) were higher when Tamb and HI were high compared with when Tamb and HI were low. CONCLUSIONS: Because of the environmental conditions and race duration, the Falmouth Road Race provides a unique setting for a high incidence of EHS. A clear relationship exists between environmental stress, especially as measured by Tamb and HI, and the occurrence of EHS or other EHI. Proper prevention and treatment strategies should be used during periods of high environmental temperatures as the likelihood of runners experiencing EHS is exacerbated in these harsh conditions.

Hypohydration and hyperthermia impair neuromuscular control after exercise.

PURPOSE: This study aimed to evaluate the effects of hypohydration and hyperthermia during exercise on movement technique and postural control. METHODS: Twelve healthy men (age = 20 ± 2 yr, height = 182 ± 8 cm, mass = 74.0 ± 8.2 kg, V˙O2max = 57.0 ± 6.0 mL·kg·min; mean ± SD) completed four randomized test sessions: euhydrated temperate (EUT), euhydrated hot (EUH), hypohydrated temperate (HYT), and hypohydrated hot (HYH). Temperate and hot conditions were performed in 18.0°C ± 0.2°C, 50.0% ± 3.5% relative humidity, and 34.0°C ± 0.3°C, 45.0% ± 4.5% relative humidity, respectively. Movement technique and postural control were assessed before exercise (PRE), after exercise (POST), and after recovery (REC). Movement technique was evaluated using the Landing Error Scoring System (LESS). Postural control was assessed using the Balance Error Scoring System (BESS) and center-of-pressure sway velocity (SV) and elliptical sway area (ESA) during a dynamic balance test. The 90-min treadmill exercise protocol (1.34-1.78 m·s; 5% grade) required subjects to walk carrying a 20.5-kg rucksack. Subjects sat quietly in the test environment during a 60-min recovery period after exercise. Repeated-measures ANOVAs with a Tukey-HSD post hoc test evaluated differences between time and condition for dependent variables. RESULTS: Exercise during HYH significantly increased LESS scores (PRE = 3.72 ± 1.73, POST = 4.42 ± 1.75) compared with HYT (3.75 ± 1.76) and EUH (3.61 ± 1.71) (P < 0.05). LESS scores remained elevated during REC for HYH compared with EUT (4.39 ± 1.47 vs 3.47 ± 2.05, P < 0.05). The HYH condition caused the greatest number of BESS errors (P = 0.02), largest ESA (P < 0.05), and highest SV (P = 0.02). Regardless of the condition, participants had the most BESS errors (P = 0.002) and highest SV (P = 0.003) during POST compared with the PRE and REC. CONCLUSIONS: Hypohydration during exercise in the heat impairs neuromuscular control. These findings suggest that physical activity in the heat while dehydrated may affect parameters associated with a higher risk of injury.