THE SPRINT

600-plus muscles, a real scan, moving

GLUTESGLUTES

HAMSTRINGSHAMS

QUADRICEPSQUADS

CALFCALF

HIP FLEXORSHIP FLEX

DELTOIDDELTOID

ONE FASCICLEFASCICLE

EPIMYSIUMEPIMYSIUM

TENDONTENDON

ONE FIBRE (CELL)FIBRE

PERIMYSIUMPERIMYSIUM

CAPILLARYCAPILLARY

ONE MYOFIBRILMYOFIBRIL

NUCLEUS (ONE OF HUNDREDS)NUCLEUS

SATELLITE CELLSATELLITE

SARCOLEMMASARCOLEMMA

MOTOR AXONMOTOR AXON

NEUROMUSCULAR JUNCTIONNMJ

ACTION POTENTIAL → T-TUBULESAP → T-TUBULES

A BANDA BAND

I BANDI BAND

Z LINEZ LINE

T-TUBULET-TUBULE

SARCOPLASMIC RETICULUMSR

ONE SARCOMERESARCOMERE

Z-DISCZ-DISC

M-LINEM-LINE

THICK · MYOSINMYOSIN

THIN · ACTINACTIN

TITINTITIN

ATP POCKETATP POCKET

CONVERTERCONVERTER

LEVER ARM + LIGHT CHAINSLEVER ARM

ACTIN-BINDING CLEFTACTIN CLEFT

MYOSIN HEADMYOSIN HEAD

LEVERLEVER

ATPATP

THICK FILAMENTTHICK

ACTINACTIN

TROPOMYOSINTROPOMYOSIN

TROPONINTROPONIN

600+skeletal muscles FACT

38% · 31%of body mass, men · women FACT

12.3 m/sBolt's top speed, 2009 FACT

< 0.1 sfoot on the ground FACT

A real scan of the human muscles and skeleton, rigged at the joints and run through a sprint. A sprint is the hamstrings braking the swinging shin, the glutes and quadriceps catching the body as the foot lands, and the calf pushing the ground away — in under a tenth of a second per contact. The fastest sprinters do not swing their legs faster than you do. They hit the ground harder.

FACT Whole-body MRI of 468 adults: skeletal muscle was 38.4% of body mass in men and 30.6% in women. — Janssen et al., J Appl Physiol 2000
FACT The count of muscles is 600-plus — about 640 is often quoted. The number depends on whether a muscle's heads and parts are counted separately. — standard anatomy texts
FACT Across runners of very different top speeds, the swing of the leg took the same time — about 0.37 s. The faster runners hit the ground harder: about 1.26 times the force at 11.1 m/s compared with 6.2 m/s. — Weyand et al., J Appl Physiol 2000
FACT Usain Bolt peaked at about 12.3–12.4 m/s in the 2009 Berlin 100 m final. — Graubner & Nixdorf, New Stud Athl 2011; later laser reanalysis
FACT Muscle holds about 8 mmol of ATP per kg — only seconds of all-out work. Phosphocreatine (about 26 mmol/kg) refills it and carries the first 5–6 seconds of a sprint. It is largely spent within about 10 s. — Baker, McCormick & Robergs, J Nutr Metab 2010
MODEL The scan is a statue, so the page rigs it with twelve joints placed from the bones themselves. The joint angles are keyed by hand from published sprint ranges. The glow is a simplified version of sprint EMG timing (hamstrings late in the swing; glutes and quads into the landing; calf in stance; hip flexors after toe-off). — Howard, Conway & Harrison, Sports Biomech 2018 (review)

EDUCATION ONLYEducation only — not medical, training or nutrition advice. Talk to a qualified professional before changing how you train or eat, especially with a health condition.

sources & credits

What is real. The body is the BodyParts3D scan; every molecule is a measured PDB structure. What is drawn. The rig and the sprint, the tissue packings, the filament lattice and the timing of every animation are models, and each panel says which numbers are measured (FACT), accepted explanation (THEORY), drawn (MODEL) or unsettled (SPECULATION).

3D anatomy: BodyParts3D, © The Database Center for Life Science (DBCLS), CC BY-SA 2.1 JP — muscle and skeleton layers; rigged and posed on this page.

Molecular structures from the RCSB Protein Data Bank (CC0): 6KN8 and 6KN7 (Yamada, Namba & Fujii, Nat Commun 2020, doi:10.1038/s41467-019-14008-1); 5H53 (Fujii & Namba, Nat Commun 2017, doi:10.1038/ncomms13969); 2MYS (Rayment et al., Science 1993, doi:10.1126/science.8316857); ATP from the wwPDB Chemical Component Dictionary. Surfaces computed by scripts/extract-muscle.mjs.

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Education only — not medical, training or nutrition advice. Talk to a qualified professional before changing how you train or eat, especially with a health condition.