The goal of this clinical trial is to learn how older adults respond to power training when the level of fatigue during exercise is different. Power training means performing fast movements with moderate loads to improve strength, power and mobility.
The main questions the study aims to answer are:
* How does the level of fatigue during power training acutely affect strength, movement, and muscle function? * How does it affect recovery, muscle soreness, and how hard the exercise feels?
Researchers will compare three power-training sessions with different fatigue levels to see which approach may be safest and most effective for older adults.
Participants will be healthy older adults aged 65 to 85 years. Each participant will complete three supervised exercise sessions on a leg press machine. The sessions will take place about one week apart.
During the study, participants will:
* Perform power training on a pneumatic leg press machine * Complete strength and mobility tests before and after exercise * Provide small blood samples to measure body responses to exercise * Rate how hard the exercise feels * Report muscle soreness for up to two days after exercise
The results may help researchers design safer and more effective power-training programs to improve strength, mobility, and recovery in older adults.
Be 65 to 85 years old.
Be able to live independently and perform everyday activities without help.
Not have regularly done resistance or strength training in the past year.
Be able to understand study instructions and communicate in the study language.
Unstable heart disease, neurological disease, acute infection, or fever.
Use of non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, in the 5 days before the study.
Use of whey protein, casein, or amino acid supplements in the month before the study.
Acute or chronic injuries to the legs or lower body muscles.
Crossover
Power Training at Different Fatigue Levels
BehavioralParticipants perform supervised power-training exercise on a pneumatic leg press. Each participant completes three exercise sessions, each separated by approximately one week. In each session, participants perform 4 sets of leg press exercise under different fatigue conditions: A) Exercise sets are terminated when movement velocity decreases by 10%. B) Exercise sets are terminated when movement velocity decreases by 30%. C) Exercise sets are terminated at 10% velocity loss, with total work matched to the 30% condition.
Maximum Voluntary Contraction (MVC)
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)
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
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.
Strength Training Data: Mean Movement Velocity
Mean concentric movement velocity (meter per second (m/s)) recorded during each leg press (exercise) repetition using the Keiser A400 Leg Press.
Strength Training Data: Power
Mean mechanical power (Watts (W)) produced during each leg press repetition recorded by the Keiser A400 Leg Press.
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