2207 Board #220 June 1 2:00 PM - 3:30 PM Effects Of 5 Days Of HIIT On Exertional Rhabdomyolysis In Trained And Untrained Individuals Katie Ertel. Marywood University, Scranton, PA. (No relationships reported) Exertional Rhabdomyolysis is potentially life threatening, and has been diagnosed in individuals who overexert themselves during exercise. Individuals who participate in exercise beyond their level of physical fitness may be at higher risk for excessive muscle breakdown due to overexertion. PURPOSE: To measure the severity of skeletal muscle breakdown via myoglobin and creatine kinase after five days of high and low intensity interval training in previously trained and untrained individuals. METHODS: 18 males and females (9 trained (TR) and 9 untrained (UT); Age: 22 ± 1) completed five consecutive days of high intensity interval training and five consecutive days of low intensity interval training with a two week washout period between. Blood was drawn at the initial visit and immediately after completion each exercise intensity period. Individuals rated their perceived muscle soreness before each exercise session. RESULTS: Levels of myoglobin in UT were significantly higher after high intensity exercise (65.2 ng/ml; p = 0.05); however, there was no significant difference between myoglobin in TR after high intensity exercise vs. baseline (41.0 ng/ml). While CK was elevated post exercise training for both groups (p < 0.01), this was higher for trained individuals (UT: 143.4 vs. TR: 203. 6 ng/ml; p < 0.01). There was no significant difference in perceived muscle soreness between TR and UT individuals; however, UT individuals experienced soreness significantly sooner (p < 0.01). Specifically, UT individuals had significantly higher perceived soreness after one day of high intensity exercise, while TR individuals experienced significant soreness after 3 and 4 days of exercise (p = 0.04, p = 0.02). There were no significant differences in perceived muscle soreness in either TR or UT individuals after low intensity exercise. CONCLUSIONS: The current study suggests that high intensity exercise results in greater muscle damage in both previously trained and untrained individuals vs. low intensity exercise; however this is greater in untrained individuals. Therefore, previously untrained individuals should take caution when beginning exercise programs that require consecutive sessions of high intensity exercise. 2208 Board #221 June 1 2:00 PM - 3:30 PM Effects of High Intensity Interval Training Frequency on 1.5 Mile Run Times in Air Force Cadets Jared Dahle1, Dale Wagner2. 1United States Air Force Academy, USAF Academy, CO. 2Utah State University, Logan, UT. Email: firstname.lastname@example.org (No relationships reported) High intensity interval training has gained popularity in military settings in recent years, but no research has investigated how varying HIIT frequency impacts performance in the cardiovascular fitness component of an official military physical fitness test. PURPOSE: Effects of varying high intensity interval training (HIIT) frequency on 1.5 mile (2.4 km) run performance in U.S. Air Force Reserve Officer Training Corps (ROTC) cadets was studied. METHODS: Twenty-seven cadets (21.6 ± 2.8 years) were stratified then randomly assigned to 3 groups: a high frequency group (HF) that performed HIIT 3x week, a low frequency group (LF) that performed HIIT 2x week, and a continuous training group (CG) that performed moderate intensity training 3x week. HIIT protocols consisted of 4 x 3 min intervals at 90-100% of velocity at maximal oxygen consumption (vVO2 max) with 4 min of recovery and 4 x 30s all out sprints with 4 min recovery. Baseline 1.5 mile run performance was measured, then retested at 6 and 10 weeks. RESULTS: All groups significantly improved in mean run time (LF, 7.3% + 4.2, p<0.001; HF, 9.7% + 3.5, p<0.001; CG, 8.7% + 4.8, p<0.001). No significant differences between groups were found (p>0.05). Additional workouts beyond the 6-week point yielded no significant gains in run performance for any group. CONCLUSION: Two days per week of HIIT training was as effective at improving 1.5 mile run performance as either 3 days/week of HIIT or continuous training. 2209 Board #222 June 1 2:00 PM - 3:30 PM Effects of Different Tempos of a Side-step Interval Exercise on Heart Rate and Muscle Activation Robert S. Thiebaud1, Takashi Abe2, Jonathan C. Bravo1, Nicolas Giovannitti1, Avery P. Sullivan1. 1Texas Wesleyan University, Fort Worth, TX. 2 National Institute of Fitness and Sports, Kanoya, Kagoshima, Japan. Email: email@example.com (No relationships reported) One barrier to meeting fitness recommendations may include time constraints. Finding exercises that can promote improvements in both aerobic and muscular fitness while minimizing the duration of the exercise and the required equipment are needed. One such exercise may be the side-step interval exercise. Currently, it is unknown how different tempos influence this exercise and how heart rates and muscle activation differ between tempos. PURPOSE: To investigate how different tempos of a side-step interval exercise influence heart rate and muscle activation responses. METHODS: Recreationally active men (n=8) and women (n=2) participated in this study. The average maximum oxygen uptake (VO2max) of participants was 50.1 ± 10 yrs and age was 21 ± 3 yrs. The side-step interval exercise consisted of moving from side to side repetitively over a two-meter distance for 1 minute with 1-minute rest periods in between sets. Four sets of these exercise intervals were performed. The fast (112 bpm) or slow (84 bpm) tempo was randomly assigned during the first exercise session with the other tempo being used in the next visit. Surface electromyography (EMG) measured muscle activation of the vastus lateralis and a heart rate monitor (Polar) measured heart rate (HR). Two-way repeated measures ANOVA analyzed differences between tempos and sets. Pearson product moment correlations analyzed associations between VO2max, HR response and muscle activation. Statistical significance was set at p<0.05. RESULTS: Slow tempos produced significantly lower amounts of muscle activation compared to the fast tempos [46% vs. 59% of the maximum isometric voluntary contraction muscle activation (EMGmax), p=0.002]. HR significantly increased at the end of sets 3 (150 ± 8 bpm, p=0.012) and set 4 (152 ± 8 bpm, p=0.001) when compared to set 2 (146 ± 8 bpm). The fast tempo produced significantly greater HR than the slow tempo (82% HRmax vs. 70% HRmax, p<0.001). A significant inverse relationship was also found between VO2max and vastus lateralis muscle activation (r=-0.855, p=0.003), fast tempo HR (p=-0.896, p<0.001) and slow tempo HR (p=-0.924, p<0.001). CONCLUSIONS: Side-step interval exercise acutely produces sufficient levels of HR and muscle activation to promote improvements in aerobic and muscular fitness but future chronic studies are needed. 2210 Board #223 June 1 2:00 PM - 3:30 PM Sprint Interval Training and Power Output In College Age Females Jenna Thompson, Sophie Olson, Leigha Embertson, Mark Blegen, FACSM. St. Catherine University, St. Paul, MN. (Sponsor: Mark Blegen, FACSM) (No relationships reported) 616 Copyright © 2017 by the American College of Sports Medicine. 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