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# Athletic capacity: strength, power, endurance and sex differences

- Concept
- Exam priority: medium

Sprints run on stored phosphocreatine, middle distances on fast glycolysis, and long events on aerobic metabolism of glycogen and fat.

Updated Nov 13, 2026

Also called: Energy systems in sport, Phosphagen, glycolytic and aerobic systems, VO₂max

## Key points

- Phosphagen system: highest rate of ATP supply, lasts about 8–10 s of maximal effort (100 m sprint, jumps, lifts).
- Anaerobic glycolysis: about half that rate, sustains maximal effort for roughly 1–2 min (400–800 m) and produces lactate and H⁺.
- Aerobic system: lowest rate but practically unlimited duration while glycogen and fat last (marathon, cycling stages).
- Maximal muscle force ≈ 3–4 kg per cm² of cross-sectional area in both sexes; training raises it mostly through hypertrophy and better recruitment.
- Sex gap in elite performance (≈ 10–12% in running and swimming) emerges at puberty with the rise in male testosterone.
- VO₂max sets the ceiling for endurance; the lactate threshold (as % of VO₂max) and running economy decide race pace.

## What it is

Muscle strength depends mainly on its cross-sectional area, power on force times speed of contraction, and endurance on fuel stores, fibre type and the O₂ supply. Three energy systems resupply ATP: the phosphagen system (ATP plus phosphocreatine) gives the highest power for seconds, anaerobic glycolysis gives high power for about a minute or two, and the aerobic system gives lower power for as long as fuel lasts. On average men outperform women by about 10% in running and swimming, mainly because of testosterone-driven differences in muscle mass, hemoglobin and heart size; strength per unit of muscle area is similar.

## Key facts

- Strength is the maximal force a muscle can produce; power is the rate of work (force × velocity) and peaks at intermediate loads.
- Endurance correlates with muscle glycogen: a high-carbohydrate diet before an event roughly doubles time to exhaustion compared with a high-fat diet.
- Fast (type II) fibres give power, slow (type I) fibres give endurance; the proportion is largely inherited and only partly trainable.
- Elite endurance athletes have large hearts and stroke volumes and higher capillary and mitochondrial density in muscle.
- Women have on average lower hemoglobin and smaller hearts, but similar fatigue resistance and often better fat oxidation in long events.

## Typical VO₂max values in adults (wide individual variation)

| Parameter | Value |
| --- | --- |
| Sedentary men | ≈ 35–45 mL·kg⁻¹·min⁻¹ |
| Sedentary women | ≈ 27–38 mL·kg⁻¹·min⁻¹ |
| Elite endurance men | ≈ 70–85 mL·kg⁻¹·min⁻¹ |
| Elite endurance women | ≈ 60–75 mL·kg⁻¹·min⁻¹ |

Approximate values for a healthy adult at rest; each laboratory sets its own ranges.

## Energy systems by event (dominant system; all contribute in every effort)

| Event | Duration | Dominant system | Main fuel |
| --- | --- | --- | --- |
| Shot put, jump, 100 m | 2 h | Aerobic | Fat and glycogen; glucose from the liver |
| Football, basketball | Intermittent | All three in turns | Phosphocreatine refilled aerobically between sprints |

## Memory aid

Spark, flame, furnace: phosphocreatine sparks a sprint, glycolysis flames a lap, aerobic furnace burns a marathon.

## Test yourself

Think of the answer, then tap the question to see it.

## Which energy system supplies most ATP in a 100 m sprint, and why can it not last longer?

The phosphagen system: it regenerates ATP fastest but phosphocreatine stores are small and are largely used up in about 10 s.

## Why does a 400 m runner feel intense muscle burning at the finish?

Anaerobic glycolysis supplies much of the ATP; lactate and H⁺ accumulate, acidifying the muscle and causing pain and fatigue.

## Is a woman's muscle weaker per unit of cross-sectional area than a man's?

No. Force per cm² is similar; men are stronger on average because they have more muscle mass, driven by testosterone.

## What limits pace in a marathon more than VO₂max itself?

The fraction of VO₂max that can be held without lactate accumulation (lactate threshold), running economy and glycogen stores.

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## Connections

## Related topics 5

- [Exercise and training physiology](https://durgical.com/en/physiology/exercise-and-training-physiology/)
- [Fast and slow fibers, energy and fatigue](https://durgical.com/en/physiology/fast-and-slow-fibers-energy-and-fatigue/)
- [Muscle hypertrophy, atrophy and remodeling](https://durgical.com/en/physiology/muscle-hypertrophy-atrophy-and-remodeling/)
- [Motor units, recruitment and summation](https://durgical.com/en/physiology/motor-units-recruitment-and-summation/)
- [Testosterone and its actions](https://durgical.com/en/physiology/testosterone-and-its-actions/)

## In Biochemistry 3

- [Exercise metabolism](https://durgical.com/en/biochemistry/topics/exercise-metabolism/)
- [Creatine, phosphocreatine and creatinine](https://durgical.com/en/biochemistry/topics/creatine-phosphocreatine-and-creatinine/)
- [Lactate](https://durgical.com/en/biochemistry/molecules/lactate/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance](https://pmc.ncbi.nlm.nih.gov/articles/PMC6391653/) (Endocrine Reviews (PMC), 2018); [Lactate Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/lactate-test/) (MedlinePlus, US National Library of Medicine, 2024); [Benefits of Exercise: MedlinePlus](https://medlineplus.gov/benefitsofexercise.html) (MedlinePlus, US National Library of Medicine, 2024).

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