Both slow-twitch and fast-twitch muscle fibers shrink over time, but fast-twitch fibers experience a much greater reduction in size and number when individuals fail to challenge them properly.
Lifting heavy weights remains essential for preserving muscle mass during aging, according to bodybuilding legend Arnold Schwarzenegger. Writing in the Arnold’s Pump Club newsletter, Schwarzenegger highlights the traditional belief that lighter weights only train slow-twitch fibers while heavy weights target fast-twitch fibers.
However, a study published in Frontiers in Physiology challenges that notion. The research found that both heavy and light weights can build both fiber types when sets are taken to failure.
The primary challenge with lighter weights is that exercisers often struggle to recognize when they have actually reached failure, making fast-twitch recruitment difficult.
“The likely reason is how your body recruits muscle,” Schwarzenegger said in his newsletter.
“It calls on slow-twitch fibres first and brings in fast-twitch as effort climbs,” Schwarzenegger said.
“Light sets taken to failure eventually get there. Heavy sets may get there sooner and keep those fibres working longer,” Arnold said.
While high-rep sets with light weights work, they require significantly more time in the gym to match the stimulus provided by heavier loads. Schwarzenegger recommends that everyone push heavier weights relative to their individual strength at least once or twice per week.
The light-and-heavy method integrates easily into existing workout routines. Exercisers select a compound movement such as a squat, deadlift, bench press, or dumbbell row at the start of a session, using a weight that permits roughly five safe repetitions with good form.
Athletes complete two or three heavy sets before transitioning to higher-rep, lighter-weight exercises. Maintaining proximity to failure during both heavy compounds and lighter isolation work helps recruit additional muscle fibers as effort increases.
Research published in Frontiers in Physiology shows that light weights can build both slow-twitch and fast-twitch fibers, provided the sets are taken to absolute muscular failure.
Heavy sets recruit fast-twitch muscle fibers sooner and keep them working longer than light sets, reducing the total time required in the gym to achieve the same muscle-building stimulus.
Arnold Schwarzenegger recommends lifting heavier weights relative to your personal strength at least once or twice per week as part of an overall resistance training program.
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