(28) A MULTI-INGREDIENT PRE-WORKOUT SUPPLEMENT AND EXERCISE DURATION ACUTELY AFFECTED MUSCLE SIZE AND QUALITY FOLLOWING HIGH-INTENSITY FUNCTIONAL TRAINING

Pre-workout formulations often contain ingredients thought to facilitate blood flow to working muscles. By enhancing oxygen and nutrient delivery, supplementation might help deliver the energy necessary to sustain greater effort during high-intensity functional training (HIFT). HIFT workouts will often combine traditional aerobic, resistance training, and gymnastic modalities into a circuit to be performed, for example, for ‘as many repetitions as possible’ (AMRAP) within a time limit. This design presents several logistical limitations for observing physiological responses during exercise. Ultrasound represents a potential, non-invasive method for observing increases in blood flow to exercising musculature but has yet to be used following HIFT.

Purpose: To compare the acute effects of a pre-workout supplement and HIFT workout duration on muscle architecture in experienced adults.

Methods: Twenty-two men (n = 12) and women (n = 10) who possessed at least two years of HIFT experience (29.3 ± 7.1 years; 171.4 ± 7.4 cm; 80.5 ± 15.6 kg) volunteered for this crossover-designed, placebo-controlled study. Participants completed four experimental conditions, once per week, in random order, where pre- (PRE) and post-exercise (POST) ultrasound panoramic images were collected of vastus lateralis (VL) and rectus femoris (RF). Images were subsequently analyzed to measure muscle cross-sectional area (CSA; cm²) and echo intensity (EI; arbitrary units [au]). Immediately after PRE, participants consumed either a multi-ingredient pre-workout supplement (S) or non-caloric placebo (P), rested 40 minutes, and then completed a 5- (5S and 5P) or 15-minute (15S and 15P) AMRAP circuit of rowing (men: 9 kcal; women: 7 kcal), six barbell thrusters (men: 43.1 kg; women: 29.5 kg), and three box jumps (men: 0.6 m; women: 0.5 m).

Results: Separate repeated measures analysis of variance revealed significant (p < 0.05) condition x time interactions for CSA and EI in both muscles. Except for VL CSA (5P: 35.9 ± 8.0 cm² vs. 5S: 35.0 ± 8.4 cm²; p = 0.018), no differences were seen at PRE. At POST, an approximately ~8.8 – 11.7% greater increase in CSA (RF & VL, p < 0.05) was seen in both S workouts compared to both P workouts, and then EI was greater at POST during 5S (RF: 100 ± 20.9 au; VL: 100.1 ± 20.3 au; p = 0.012) compared to 5P (RF: 93.2 ± 19.3 au; VL: 93.5 ± 17.5 au). Significant (p < 0.05) condition x sex differences were also noted for EI (RF & VL), where between supplement condition differences at the same workout duration were seen in women but not men. For women, EI was greater at POST during 5S (RF: 98.8 ± 24.3 au; VL: 101.9 ± 23.2 au) compared to 5P (RF: 84.7 ± 19.8 au; VL: 89.3 ± 19.1 au) but lower at POST during 15S (RF: 91 ± 24.6 au; VL: 94.7 ± 18.4 au) compared to 15P (RF: 99.5 ± 23.6 au; VL: 105.6 ± 22.3 au). No other differences were noted between supplement conditions.

Conclusions: The multi-ingredient pre-workout supplement led to a greater increase in muscle size compared to placebo. However, its effect on post-exercise muscle quality was influenced by workout duration and sex, where reductions were greater (i.e., greater EI) following the 5-minute bouts but lesser after the 15-minute bouts in women only. PRACTICAL APPLICATION: These data suggest that the pre-workout supplement used in this study may enhance blood flow to working muscle, potentially altering nutrient availability, cell swelling, and/or post-exercise muscle damage.





Acknowledgements: This study was funded by Shifted, LLC.