The Effect of Beetroot Juice on Muscle Strength and Muscle EMG Activity During Isokinetic Performance

Participants completed two experimental sessions in a randomized, double-blind, placebo-controlled crossover design separated by a minimum 3-day washout period. Prior to each session, participants were instructed to avoid nitrate-rich foods, strenuous exercise, antibacterial mouthwash, chewing gum, and tooth brushing.

All testing sessions were performed in the morning following an overnight fast. Upon arrival, anthropometric measurements were obtained and participants consumed either a nitrate-rich beetroot juice supplement (highNO) or nitrate-depleted placebo (lowNO). Following a standardized 2-hour absorption period, surface EMG electrodes were placed on the vastus medialis oblique (VMO) and vastus lateralis oblique (VLO) muscles according to SENIAM guidelines. Capillary blood samples were collected before exercise and 3 minutes after the fatigue protocol for blood lactate assessment.

Participants then completed a standardized 10-minute warm-up followed by isokinetic testing using a Biodex dynamometer. Testing was performed on the dominant lower limb at angular velocities of 180°/s, 60°/s, and 240°/s. Three maximal repetitions were performed at 60°/s and 180°/s, while a 30-repetition fatigue protocol was completed at 240°/s. Outcome measures included peak torque, peak power, total work, torque-angle variables, EMG activity, and blood lactate concentration.

Inclusion criteria

• age ≥18 years,
• participation in at least three structured training sessions per week,
• absence of musculoskeletal injuries within the previous 12 months

Exclusion criteria

• smoking,
• any injury within the past year