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During a strength training session, the body typically engages slow-twitch muscle fibers first. Slow-twitch fibers, also known as Type I fibers, are more resistant to fatigue and are primarily used for endurance activities. These fibers are beneficial for stabilizing the muscles and sustaining prolonged contractions, which is necessary at the beginning of a workout when the body is preparing for more intense exercises.

As the session progresses and the demands on the muscles increase, the body will later recruit fast-twitch fibers, including Type IIb fibers, which are designed for explosive and powerful movements. However, the initiation of strength training is characterized by the use of slow-twitch fibers to build a foundation of strength and stability, ensuring proper form and reducing the risk of injury during more demanding phases of the workout.

Thus, starting with slow-twitch fibers sets the stage for a safe and effective strength training session, making it the correct choice for the type of muscle engaged first.