Muscle Strength, Power and Work: Key Determinants of Athletic Performance

Ever wondered why a powerlifter can heave a barbell off the floor but gasses out after ten seconds, while a marathon runner can jog for hours but couldn’t budge that same barbell? The answer lies in three distinct but connected properties of muscle: strength, power, and endurance. Understanding how these work is central to exercise physiology, and it explains almost everything about how athletes train, compete, and eventually fatigue.

What makes a muscle “strong”?
Bigger fibres, greater force
Work and power are not the same thing
The eight-second ceiling
Why power fades so fast
Endurance: winning the long game
Glycogen: the athlete’s fuel tank
What this means for training

What makes a muscle “strong”?

Muscle strength is simply the maximum force a muscle can generate during a single contraction. It sounds intuitive, but the underlying physiology has a neat twist: the maximum contractile force generated per unit cross-sectional area of muscle tissue is roughly the same across individuals and across muscle groups. Researchers describe this as a muscle’s “specific tension,” and it turns out to be a strikingly conserved property, holding true not just from person to person but across muscles of very different sizes throughout the animal kingdom, following a rule that traces back to observations first made by Galileo.

If the force each square centimetre of muscle can produce is fairly fixed, then the only real lever left to pull is size. This is why a muscle’s physiological cross-sectional area shows a near-linear relationship with its maximum force output. In plain terms: a bigger muscle, with more muscle fibres arranged in parallel, can pull harder than a smaller one, almost regardless of who the muscle belongs to.

Bigger fibres, greater force

This is also why resistance training works the way it does. Lifting heavy weights over months doesn’t just make a muscle “more efficient”; it physically increases the cross-sectional area of the muscle through hypertrophy, adding more contractile filaments working side by side. More parallel fibres means more total force, even though the force generated per unit of that muscle stays roughly constant. This is also part of the reason strength differences between men and women shrink considerably once force is expressed relative to muscle cross-sectional area rather than in absolute terms.

Work and power are not the same thing

Strength tells you how much force a muscle can produce, but it says nothing about speed or duration. That’s where work and power come in, and students often confuse the two.

Work done by a muscle is calculated as the force applied multiplied by the distance over which that force acts. If you lift a 10 kg dumbbell through half a metre, the work done is the same whether you do it in one second or in ten seconds.

Power, on the other hand, factors in time. It’s the amount of work performed per unit time. Two people can do identical work, but the one who does it faster is generating more power. This is exactly why a sprinter and a weightlifter both display explosive power, even though their sports look nothing alike; both are compressing a large amount of work into a very short window of time.

The eight-second ceiling

Human muscle has an upper limit on how much power it can generate, and that limit only holds for a very brief window. All the muscles in the body, working together, can produce a peak output in the range of a few thousand kilogram-metres per minute, but only for about eight to ten seconds. This ceiling exists because that burst of effort is fuelled almost entirely by the phosphagen or ATP-PC system, an anaerobic energy pathway that supplies energy instantly but has a tiny fuel tank. This alactic anaerobic system is built to sustain maximal effort for roughly ten seconds before the body has to switch to slower, less explosive ways of making energy.

This is precisely why a 100-metre sprinter can hold top speed for barely eight to ten seconds even over a race that technically lasts longer, and why a single maximal vertical jump or a one-rep max lift represents close to the absolute ceiling of what human muscle can output.

Why power fades so fast

Push past that eight-to-ten-second window and something dramatic happens: power output drops off a cliff. Within the next minute of continued activity, muscle power falls to less than half of its initial maximum. Push on for half an hour, and output crashes to roughly a fifth of what it was at the start.

This isn’t muscles being lazy; it’s a direct consequence of energy system handoffs. Once the phosphagen stores are used up, the body leans on anaerobic glycolysis, which can resynthesise ATP quickly but at a much lower rate and with the unwelcome side effect of lactate accumulation. Sustained efforts above a certain “critical power” threshold show a continuous, measurable decline in muscle efficiency over time, with phosphocreatine and pH levels shifting progressively until the muscle simply can’t keep pace. Beyond a couple of minutes, the aerobic system takes over as the dominant energy supplier, and that system, while far more sustainable, simply cannot match the power output of the anaerobic pathways.

This decline curve is why sports are so cleanly divided by duration. A shot-putter or a weightlifter trains almost exclusively for that eight-to-ten-second window. A middle-distance runner has to manage the steep drop that follows. And a marathoner has essentially given up on peak power altogether, optimising instead for a much lower, steady output that can be maintained for hours.

Endurance: winning the long game

Endurance is the capacity to sustain exercise for extended periods, and unlike raw strength or peak power, it depends far less on muscle size and far more on fuel supply. Specifically, endurance is closely tied to how much glycogen, the storage form of carbohydrate, is available in the muscles and liver.

Glycogen: the athlete’s fuel tank

The body stockpiles carbohydrate largely as glycogen, with skeletal muscle holding roughly 400 grams and the liver holding around another 100 grams, alongside a small amount of circulating blood glucose. During prolonged, moderate-to-intense activity, this stored glycogen becomes the primary fuel for continued ATP production in working muscle. As those reserves start to run low, the muscle cell can no longer regenerate ATP fast enough to maintain intensity, and the depletion of muscle glycogen is directly linked to the onset of fatigue, including reduced force output during maximal contractions.

This is exactly why athletes preparing for long events pay close attention to carbohydrate intake in the days leading up to competition, a practice often called carbohydrate loading. Even guidance closer to home reflects this principle: the Dietary Guidelines for Indians from the ICMR-National Institute of Nutrition emphasise adequate carbohydrate intake alongside physical activity as part of maintaining energy balance and performance capacity, a point that matters as much for a college athlete training for a state meet as it does for an elite marathoner.

What this means for training

Put together, strength, power, and endurance point to three very different training priorities:

Building strength means increasing muscle cross-sectional area through progressive resistance training, since force capacity scales with muscle size rather than any special “trick” a muscle learns.

Building power means training the anaerobic energy systems and neuromuscular coordination needed to produce force rapidly, typically through explosive, short-duration efforts with full recovery between sets.

Building endurance means training the aerobic system and, just as importantly, managing glycogen stores through both training adaptations and nutrition, so the muscle has enough fuel to keep going long after the anaerobic systems have tapped out.

A well-rounded athlete, or even a well-rounded training programme for a non-athlete, usually needs a bit of all three, tailored to the specific demands of the activity in question.

What do you think? If you had to train for just one of these three qualities, strength, power, or endurance, which would you pick for your favourite sport, and why do you think that quality matters more than the other two in that context?

How useful was this post?

Click on a star to rate it!

Average rating 0 / 5. Vote count: 0

No votes so far! Be the first to rate this post.

References

PDF 📄

Table of Contents

What makes a muscle “strong”? 🔗

Bigger fibres, greater force 🔗

Work and power are not the same thing 🔗

The eight-second ceiling 🔗

Why power fades so fast 🔗

Endurance: winning the long game 🔗

Glycogen: the athlete’s fuel tank 🔗

What this means for training 🔗