Acute Effects of Physical Activity Under Laboratory Conditions on Muscle Architecture Measured Using B-Mode Ultrasound

INTERVENTION: Group 1: 20 min of cycling at the participant's habitual cycling intensity/resistance at 70‐80 revolutions per minute Group 2: 20 min of walking at the participant's habitual brisk walking speed Group 3: Stair climbing involving 300 steps, alternating between 50 steps ascending and 50 steps descending (150 steps ascending and 150 steps descending in total) Group 4: 20 min of sitting as a passive control condition CONDITION: Acute changes in skeletal muscle architecture following physical activity PRIMARY OUTCOME: Acute changes in medial gastrocnemius muscle thickness (mm), measured by B‐mode ultrasonography. Muscle thickness will be assessed before the intervention (at 15 and 20 minutes after arrival) and at 1, 5, 10, 15, and 20 minutes after the intervention. SECONDARY OUTCOME: Secondary outcome 1: Acute changes in vastus lateralis muscle thickness (mm), measured by B‐mode ultrasonography. Muscle thickness will be assessed before the intervention (at 15.5 and 20.5 minutes after arrival) and at 1.5, 5.5, 10.5, 15.5, and 20.5 minutes after the intervention. ; Secondary outcome 2: Acute changes in pennation angle of the vastus lateralis, measured by B‐mode ultrasonography. Pennation angle will be assessed before the intervention (at 15.5 and 20.5 minutes after arrival) and at 1.5, 5.5, 10.5, 15.5, and 20.5 minutes after the intervention. ; Secondary outcome 3: Acute changes in pennation angle of the medial gastrocnemius, measured by B‐mode ultrasonography. Pennation angle will be assessed before the intervention (at 15 and 20 minutes after arrival) and at 1, 5, 10, 15, and 20 minutes after the intervention. INCLUSION CRITERIA: Male participants with a body fat percentage of <20% and female participants with a body fat percentage of <30%.