Acute Power Training Effects in Older Adults

Maximum voluntary contraction (MVC) will be assessed to determine the maximum force-generating capacity of the leg extensors using an isokinetic dynamometer (Humac Norm). Simultaneously, muscle activity will be recorded using surface electromyography (EMG; Delsys EMG system).

Primary outcome metric: Peak torque (Nm) obtained from three maximal isometric trials recorded on the dynamometer, combined with EMG amplitude (µV) to quantify muscle activation. Interpretation: Higher torque values indicate greater knee extensor strength. EMG amplitude reflects the level of muscle activation during maximal voluntary effort.

Interpretation: Higher force values indicate greater leg muscle strength. EMG values indicate the level of muscle activation during the maximal effort.

Rate of torque development (RTD) will be assessed to determine how quickly participants can generate torque with their leg extensors. This will be measured using an isokinetic dynamometer (Humac Norm), which records joint torque, alongside surface electromyography (EMG; Delsys EMG system), which measures muscle activation. This parameter provides insight into neuromuscular responses to different levels of power training-induced fatigue.

Metric: Peak rate of torque development (Nm/s) calculated from three maximal trials, together with EMG amplitude (µV). RTD will be calculated as the slope of the torque-time curve over a specified time interval (e.g., 0-100ms, 100-200 ms).

Muscle activity will be assessed by recording the electrical signals of the leg muscles during the leg press exercise using surface electromyography (sEMG; Delsys EMG system). This method enables quantification of muscle activation and fatigue-related changes in neuromuscular function.

Surface electrodes will be placed on three key thigh muscles: the vastus lateralis, vastus medialis, and biceps femoris.

Metric: EMG amplitude (µV), derived from the recorded electrical signals, representing the level of muscle activation during exercise.

Mean concentric movement velocity (meter per second (m/s)) recorded during each leg press (exercise) repetition using the Keiser A400 Leg Press.

Mean mechanical power (Watts (W)) produced during each leg press repetition recorded by the Keiser A400 Leg Press.

Total number of repetitions (count) completed during each exercise session on the leg press.

Muscle oxygenation will be assessed to determine oxygen availability in the thigh muscle (vastus lateralis) during and after exercise using near-infrared spectroscopy (NIRS). In addition, a vascular occlusion test will be performed to evaluate muscle oxygen extraction and the recovery kinetics of oxygenation following transient blood flow restriction.

Metric: Muscle oxygen saturation (%; e.g., SmO₂), as well as reoxygenation rate and amplitude following occlusion.

Small blood sample will be taken to measure lactate, in millimoles per liter analysed through standard laboratory tests, including Enzyme-Linked Immunosorbent Assay (ELISA).

A Small blood sample will be taken to measure blood gas levels (blood oxygen/carbon dioxide levels) using standard laboratory tests, including Enzyme-Linked Immunosorbent Assay (ELISA).

Small blood samples will be taken to measure creatine kinase (CK), an enzyme that increases in the blood when muscles are damaged or stressed.

Metric: CK concentration in units per liter (U/L).

Five-Repetition Sit-to-Stand (5xSTS) test: Participants stand up from a chair repeatedly. An inertial measurement unit (DynaPort MoveTest, McRoberts, The Hague, NL) measures speed (meters per second (m/s)), movement duration (s) , and power (W).

Countermovement Jump (CMJ): Participants jump vertically from a standing position. Jump height (cm), force (Nm), and power (W) are measured using KINVENT force plates.

Stair Ascent Test (SA): Participants climb a set of stairs while wearing an inertial measurement unit (DynaPort MoveTest, McRoberts, The Hague, NL), which measures speed (m/s), movement duration (s), distance (cm), and power (W).

30-Second Sit-to-Stand (30sSTS) Tests: Participants stand up from a chair repeatedly. An inertial measurement unit (DynaPort MoveTest, McRoberts, The Hague, NL) measures speed (m/s), movement duration (s), and power (W).

Perceived exertion will be assessed using the OMNI Resistance Exercise Scale (OMNI-RES). Participants will rate their level of effort after each exercise set during the leg press sessions. The scale ranges from 1 (no exertion at all) to 10 (maximum effort), with higher scores indicating greater perceived exertion.

Delayed onset of muscle soreness (DOMS) will be assessed using a Visual Analog Scale (VAS). Participants will rate perceived soreness in the leg muscles on a scale from 0 (no soreness) to 10 (worst possible soreness), with higher scores indicating greater muscle soreness.