by Sutter Wyatt, PT, DPT at CPR: Physical Therapy + Performance

Have you ever had moments in your recent years of life where you felt like you didn’t quite have the spring in your step like you once did? Maybe your child or grandchild challenged you in a foot race and you lost for the first time without “letting them win”. Or maybe your brain is still telling you that you are 21 again but your body is moving at .75x speed and your feet get tripped up resulting in a fall. While sometimes these instances can bring laughter and the saying “I don’t move quite like I used to” or “just wait until you reach my age”, it can also pose as a barrier for us to continue to do the things we love to do whether that be ski, bike, pickleball, play, golf, hike, or help a neighbor. No one is invincible to aging, and accepting aging can be more challenging for some than others, but there are key physiological processes that occur within our musculature that cause us to feel like our bodies are slowing down faster than we desire. The good news is, we can also do things to make positive adaptations in our musculature to keep the spring in our step.   

Speed 

That moment when your kid beats you in a sprint or your reaction time feels delayed isn’t just “getting older”—it’s a reflection of changes happening at the neuromuscular level. Speed depends on how fast your brain can send a signal, how quickly your muscles can respond, and how powerful that response is. All three are impacted by aging. 

Starting as early as our late 20s to early 30s, we see gradual declines in motor unit firing rate, rate of force production, and muscle fiber size (fast twitch fibers especially). This causes our movements that used to feel explosive more muted. One of the most frustrating aspects of aging is that your intent doesn’t change. Your brain still knows how to move fast. It still expects your body to respond the same way it always has. But the body lags, and this miscommunication between neurological intent and muscular output is why people describe feeling “clumsy,” slow, or uncoordinated. It’s also why falls become more common after 30. Reaction time and rapid force production are protective qualities, and when they fade, the margin for error shrinks. 

Type I vs Type II Muscle Fibers (And Why They Matter) 

There are two types of muscle fibers, with a hybrid “floater” muscle fiber, that can effectively transition between either depending on our training stimulus and lifestyle choices. Type I muscle fibers are traditionally known as our slow twitch muscle fibers. These fibers are our endurance fibers. They do not fatigue easily, they produce lower force and speed, and are advantageous for activities like walking, posture, marathons, long workdays, carrying babies all day etc. Type II muscle fibers are our fast twitch muscle fibers which are categorized into type IIa and type IIb. Type IIa (hybrid) muscle fibers are capable of relatively high forces and speed production and are moderately fatigue resistant. These fibers are more advantageous for relative power, 1 mile run, athletic endeavors, skiing. 

Type IIb muscle fibers are our highest force and speed producing fibers, they fatigue quickly but are very explosive. These fibers are advantageous for jumping, sprinting, golf swing speed, power cleans, throwing, getting out of the way of a threat, or catching yourself from falling. As we age, Type II fibers are preferentially lost or converted, especially Type IIb fibers. This doesn’t mean they disappear overnight, but without the right stimulus, the body essentially “down-regulates” them. Why? Because the body adapts to what it needs. If you stop sprinting, jumping, lifting explosively, or moving fast—your body decides those fibers aren’t necessary. 

Physiological Changes After 30 

Several key changes contribute to this fiber shift: 

1. Decreased Neural Drive 
The nervous system becomes less efficient at rapidly recruiting high-threshold motor units. 

2. Selective Atrophy of Fast-Twitch Fibers 
Type II fibers shrink faster than Type I fibers with inactivity or aging. 

3. Hormonal Changes 
Gradual reductions in testosterone, growth hormone, and IGF-1 impact muscle protein synthesis and recovery. 

4. Reduced Tendon Stiffness 
Tendons become less elastic, reducing force transfer and explosive capacity. 

5. Slower Recovery 
Which often leads people to self-limit intensity, further accelerating decline. 

The takeaway: aging isn’t just about muscle loss—it’s about losing speed-specific capacity. 

Training to Slow the Transition 

Here’s the good news: muscle fiber shifts are not one-way streets. While we can’t stop aging, we can absolutely slow, and partially reverse, the decline in fast-twitch capacity with intelligent training. The issue is the rate of force development or how fast we can use the strength we have. In our childhood and adolescent years our nervous systems primed for speed. We sprint, jump, react, and play constantly. Adults train slowly, sit often, and avoid high-velocity movement. This habit only quickens the transition to slower movement speed. Some key training principles include: 

1. Move Fast on Purpose 
Speed must be trained at speed. Slow training alone does not maintain fast fibers. 

2. Low Volume, High Intent 
Explosive work does not require long workouts. Quality beats quantity.

3. Progressive Exposure 
You don’t need to start with box jumps or sprints—start where your body can handle speed safely. 

Plyometrics, Fast Movements, and Intervals 

Incorporating speed and power into your program can look like: 

• Plyometric exercises (jump variations, hops, bounds, box jumps, depth jumps) 

• Medicine ball throws (especially for upper body speed or rotational speed: golf, baseball, softball, pickleball) 

• Olympic lifting (power clean, hang clean, snatch both with barbell or dumbbell) 

• Short sprints or bike intervals 

• Fast concentric lifting with controlled lowering 

These movements stimulate Type II fibers, improve neural drive, and maintain tendon elasticity—all critical for athletic longevity. Maintaining fast-twitch function directly impacts vertical jump, golf driving distance, quickness on the pickleball court, chasing kids/grandkids, fall prevention and reaction time. Speed and power aren’t just athletic qualities, they’re functional ones. 

If speed is one of your goals for 2026 and beyond and feel like you need direction on how to safely incorporate these principles, please reach out. Our CPR team is built of skilled physical therapists and trainers who can develop a program that is safe and tailored to your specific goals.