The Fast-Twitch Fix

By Shannon Kasun, Neuroscience Specialist

Say you’re out for a stroll. You breathe in the sweet spring air. Gossiping birds fill your ears with their chatter. You test your botanical knowledge, naming each newly-sprouted flower you pass when—WHOOPS!

Your sneaker catches the lip of a subtly offset curb. Gravity tugs your body toward the cement. You’re plummeting toward the hard, unforgiving ground when—PHEW!

Your back foot swings under your stumbling body just in time. The other foot follows. Your arms flap instinctively as you regain your balance. You laugh at your clumsiness and continue your walk, now paying more attention to the uneven sidewalk.

What saved you? Fast-twitch muscle fibers.

Fast-twitch muscle fibers are responsible for short, explosive movements—like sprinting, jumping, or catching yourself during a fall. These fibers contract quickly and produce a high amount of force, making them crucial for fall prevention.

But here's the catch: as we age, our muscles begin to atrophy. While all muscle fibers shrink with age, fast-twitch fibers decline more significantly than their slow-twitch counterparts (Lexell et al., 1988). In fact, age-related muscle loss is largely driven by the reduction in fast-twitch fiber size (Milwik et al., 2013).

This loss of quick-reacting muscle fibers helps explain why older adults are especially vulnerable to falls. In the United States, unintentional falls are the leading cause of injury and injury-related deaths among adults aged 65 and older (CDC, 2023). Without the explosive strength provided by fast-twitch fibers, older individuals often can’t catch themselves mid-stumble—they don’t bounce back; they hit the ground. And too often, they end up in the hospital.

Hospitalizations and injuries typically lead to periods of bedrest and inactivity. Shockingly, just 10 days of bedrest can result in a 15.6% loss of lower extremity strength (Kortebein et al., 2007). This sets off a dangerous cycle: muscle loss → more falls → more injuries → further muscle loss. This cascade can severely impact health and overall quality of life.

Most alarmingly, the mortality risk after just a single fall is significant. One study found that within the year following a fall, older adults had a 33% higher risk of death (Bandeen-Roche et al., 2015). Falls, then, are not just a matter of bruises—they are a serious, life-threatening event for older adults.

The decline isn’t irreversible. Research shows that even in the “oldest old,” fast-twitch muscle fibers can be rebuilt with the right interventions (Kryger & Anderson, 2007).

To preserve and rebuild these powerful fibers, focus on:

Resistance Training

Heavy, progressive resistance training is essential for recruiting and strengthening fast-twitch fibers. In one study, 12 weeks of heavy resistance training increased the size of fast-twitch fibers in frail older adults (Kryger & Anderson, 2007).

Protein Intake

Protein provides the building blocks for muscle repair and growth. Aim for at least 25g of protein per meal, evenly distributed across the day. This amount is enough to activate mTOR, a signaling pathway that promotes muscle protein synthesis (Trommelen et al., 2023).

Vitamin D

Vitamin D inhibits myostatin, a protein that suppresses muscle growth. Keeping myostatin levels low supports muscle building.

Omega-3 Fatty Acids

Omega-3s not only reduce muscle protein breakdown but also enhance muscle protein synthesis—a double boost for muscle health (Therdyothin et al., 2023).

Fall prevention isn’t just about being careful—it’s about being strong and reactive. And the strength to react begins with your fast-twitch muscle fibers. Whether you’re 25 or 85, it’s never too late to train for resilience. With resistance training, balanced nutrition, and the right supplements, you’re not just building muscle—you’re building longevity.

References 

Lexell et al., 1988 - https://pubmed.ncbi.nlm.nih.gov/3379447/ 

Milwik et al., 2013 - https://pubmed.ncbi.nlm.nih.gov/23425621/ 

CDC, 2023 - https://www.cdc.gov/mmwr/volumes/72/wr/mm7235a1.htm#:~:text=The%20percentage%20of%20older%20adults%20who%20reported%20falling%20ranged%20from,than%20among%20women%20(68.3). 

Kortebein et al., 2007 - https://pubmed.ncbi.nlm.nih.gov/17456818/ 

Bandeen-Roche et al., 2015 - https://pubmed.ncbi.nlm.nih.gov/26297656/ 

Kryger & Anderson, 2007 - https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0838.2006.00575.x?casa_token=ji4owZtGdmwAAAAA%3AEBqzO8MshquFSeWzlf9kwuD8FFiFhxWyfJfp7qVPGZuYD1BBU1lRndPaxGBQ4etiMZk-xF1-rHpqf7Dh 

Trommelen et al., 2023 - https://www.sciencedirect.com/science/article/pii/S2666379123005402#:~:text=Dose%2Dresponse%20studies%20have%20reported,than%2020%E2%80%9325%20g%20protein. 

Therdyothin et al., 2023 - https://www.mdpi.com/1660-3397/21/7/399