Jim Diehl CSCSFollow

Published March 11, 2026 02:58PM

After more than two decades coaching Olympic, pro, collegiate, and adult athletes, there’s one sentence I hear over and over from runners in their 40s: Why does this suddenly feel so much harder?

Most assume they’re losing endurance. That their aerobic engine is fading. That age has finally caught up. You might be feeling the same way, but I can tell you that’s rarely the full story.

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I work with many Masters athletes who still want to perform at a high level, and I can say that yes, things change in your 40s. But what changes—and what actually makes running feel harder—might not be what you think. Luckily, there are solutions to mitigate the physical changes you’re experiencing so running can feel enjoyable again.

What Changes in Your 40s

Let’s start with the physiology. Even in trained adults, VO2 max declines gradually with age—roughly 5–10% per decade if untrained. But with consistent training, that decline is far less, and, in your 40s, aerobic capacity is still highly trainable.

But the bigger shifts tend to happen elsewhere. Across both men and women, I consistently see:

• Gradual loss of fast-twitch muscle fibers
• Slight reductions in muscle mass without resistance training
• Decreased tendon stiffness (less elastic “spring”)
• Longer recovery windows between hard efforts
• Higher cumulative life stress (work, family, sleep disruption).

Most runners don’t lose their lungs in their 40s. They lose strength, power, and tissue resilience. And that changes how running feels.

Additional Shifts for Men

• Gradual decline in testosterone and growth hormone
• Slight reductions in muscle maintenance if strength work is inconsistent
• Slower recovery from high-intensity sessions.

Additional Shifts for Women

• Perimenopause may begin during this decade and hormonal fluctuations can affect energy and sleep
• Changes in collagen production may impact tendon resilience
• Greater variability in recovery week to week.

Performance may feel less predictable. Some weeks feel strong. Others feel flat. That doesn’t mean fitness is disappearing, but rather it means physiology is more dynamic.

So in all, most runners in their 40s (and in some cases 50s and beyond) the aerobic engine is still strong. But power and elasticity—the “pop” off the ground, lightness in the stride, ability to surge without thinking about—declines. When force production drops, pace feels harder, even at the same heart rate. That’s the shift. Not endurance. Force.

The Psychological Shift Nobody Talks About

There’s also something less measurable but just as real.In your 20s, fatigue feels normal. In your 40s, fatigue feels like a warning. In your 20s, you bounce back quickly. In your 40s, you’ve likely dealt with at least one injury.

By this decade, many runners have lost a little faith in their body. Effort feels heavier not just physically, but mentally.That shift alone can change how every run feels.

What Keeps You Running Strong in Your 40s

Strength, power, tendon resilience, recovery capacity, and stress tolerance become the new bottlenecks. When you train accordingly, the heaviness lifts. The runners I coach who continue to feel strong in this decade focus on three things:

1. Single-Leg Strength

Running is controlled by single-leg landings over and over again. Split squats, step-ups, and hip stability work protect the knees and hips and improve stride control. Aim for 3-4 sets; 4-12 reps.

Bulgarian Split Squats

1. Stand a few feet in front of a bench/chair and place one foot behind you on it.
2. Lower your back knee toward the floor. Keep your chest high and core engaged.
3. Push through your front heel to return to standing.
4. Complete one set on one leg, then switch.

Standing Forward Lunge

1. Step one leg forward.
2. Lower both knees until the back knee is close to the floor.
3. Push through the front foot to return to standing.
4. Complete one set on one leg, then switch.

Step‑Ups

1. Place one foot on a sturdy step or bench.
2. Push through that foot to lift your body onto the step.
3. Step back down with control.
4. Alternate legs you’re stepping up with.

Single‑Leg Squats

1. Stand on one leg with the other extended forward.
2. Bend your standing knee and squat down while keeping balance.
3. Push through your foot to stand back up.
4. This is an advanced move—use a wall for balance and don’t try to go too deep when you’re starting out.

2. Posterior Chain Strength

Glutes and hamstrings drive propulsion. Deadlifts, hip hinges, and controlled power work maintain force production and running economy. Aim for 3-4 sets; 4-10 reps.

Deadlift

1. Stand with feet hip-width apart and hinge at the hips to grab the weight. You can use a barbell, two dumbbells, or a kettlebell.
2. Keep your back straight and chest up as you drive through your heels to stand.
3. Lower the weight back down to mid-shin by pushing your hips back.

Leg Curls

1. Lie face down on the machine with the pad behind your ankles.
2. Curl your heels toward your glutes.
3. Slowly lower your legs back down.

Hip Thrust/Glute Bridge

1. Lie on your back with knees bent and feet flat on the floor.
2. Push through your heels and lift your hips up.
3. Squeeze your glutes at the top, then lower back down.

3. Calf and Achilles Capacity

Your lower leg is your spring. Slow, controlled calf raises and progressive plyometrics maintain elastic return and reduce injury risk. Go for 3-4 sets; 10-20 reps.

Calf Raise (Straight & Bent Knee)

1. Stand with your feet hip-width apart, knees straight
2. Raise your heels as high as possible.
3. Lower your heels back down slowly.
4. Complete one set, then repeat but with your knees bent.

Pogo Jump

1. Stand upright on the balls of your feet.
2. Do quick, small jumps using mostly your ankles, landing softly each time with a tiny bend in the knees.

Box Jump

1. Stand facing a sturdy box or platform.
2. Jump up, using momentum from your arms to help.
3. Land softly, stand tall, then step back down.

You can also incorporate other plyometric exercises from this guide.

When to Do the Workouts

Plyometric and explosive work should be performed at the beginning of a session, after the warm-up, when the body is fresh. Throughout the week, runners should include one session emphasizing single-leg strength and another emphasizing posterior chain strength.