(38) The Impact of HIIT on Muscle Function and SERCA1 Expression in Older Adults: A Pilot Study

Purpose: Vigorous exercise (i.e., high-intensity interval training [HIIT]) can help maintain muscle mass, strength, and independence in older adults; however, the underlying molecular mechanisms that explain this preservation are poorly understood. Therefore, the purpose is to examine changes in sarcoplasmic endoreticulum calcium ATPase 1 (SERCA 1) expression, vastus lateralis cross-sectional area (VLCSA), lower body strength, and estimated cardiorespiratory fitness (eVO2) following 12-weeks of HIIT in older adults. Methods: Four untrained older adults (81 ± 7 yr; n = 3 females) completed the total body HIIT protocol. The HIIT protocol included 9 exercises with a combination of resistance machines and free weights followed by stationary bike intervals 3 x week (45 min/session) for 12 weeks, with progressive increases in the work:rest ratios: 20s:40s (weeks 1-4); 30s:30s (weeks 5-8); and 40s:20s (weeks 9-12). Each participant’s heart rate was continually assessed from a wearable heart rate monitor and displayed as biofeedback for exercise intensity. Each participant was instructed to maintain a heart rate of 85%-95% of their heart rate maximum during the HIIT training session. Panoramic ultrasound images of the right VL were collected at baseline (PRE) and following training (POST) to estimate VLCSA. Micro biopsies from the right VL were obtained to examine changes in SERCA 1 expression at rest (1 week ± 1 day POST) using Western Blots. Glyceraldehyde 3-phosphate dehydrogenase was used as loading control to normalize all SERCA 1 expression data. Each sample was run in duplicate to ensure reliability. Muscular strength for each participant was assessed by estimating their one-repetition maximum (e1RM) using a belt squat. Starting weights were determined using a percentage of the participants body weight (males=120%, females=100%) and were gradually increased until they were unable to perform >3-5 reps. eVO2 was calculated based on 6-minute walk test performance using validated gender-specific equations. Differences (p < 0.05) between PRE and POST for each variable were identified using paired t-tests and Hedges g was used to determine effect sizes. Results: There was a significant increase in SERCA 1 expression from PRE to POST (29,564.06 ± 19,267.31 AU vs. 49,136.57 ± 2,2995.21 AU, p = 0.007, g = -4.27), as well as significant improvements in squat e1RM (75.96 ± 18.28 kg vs. 123.58 ± 30.34 kg, p = 0.036, g = -2.50) and eVO2 (27.40 ± 4.93 mL/kg/min, 34.20 ± 2.89 mL/kg/min, p = 0.047, g = -1.18). There were no significant improvements in VLCSA (9.96 ± 2.38 cm2 vs. 10.53 ± 2.95 cm2, p = 0.201, g = -0.59). Conclusions: These data suggest that the 12-weeks of HIIT increased cardiorespiratory fitness, muscle size, and strength in older adults which may be explained, in part, by an improvement in intramuscular calcium handling. Practical Applications: This study contributes to the growing body of literature citing HIIT training as an effective exercise modality to potentially ameliorate age-associated declines in lower body strength and cardiorespiratory fitness. Strength and conditioning professionals and practitioners can use this data to prescribe exercise for older adult clients. Acknowledgements: None