Muscles you need to know
- Deltoid (shoulder), biceps and triceps (upper arm), pectorals (chest), latissimus dorsi (back), rotator cuffs (shoulder joint).
- Abdominals (stomach), hip flexors (front of the hip), gluteals (buttocks).
- Quadriceps (front of thigh), hamstrings (back of thigh), gastrocnemius (calf) and tibialis anterior (front of shin).
Antagonistic pairs
- Muscles can only pull, so they work in pairs. The agonist (prime mover) contracts to cause a movement, and the antagonist relaxes.
- A fixator stabilises the origin of the agonist so it can work properly.
- Biceps and triceps: at the elbow, the biceps contract to flex the arm and the triceps contract to extend it.
- Quadriceps and hamstrings: at the knee, the hamstrings flex it and the quadriceps extend it.
- Hip flexors and gluteals: at the hip. Gastrocnemius and tibialis anterior: at the ankle.
Types of contraction
- Isotonic contractions change the muscle's length and cause movement.
- Concentric: the muscle shortens as it contracts, such as the biceps during the upward phase of a bicep curl.
- Eccentric: the muscle lengthens under tension, such as the biceps lowering the weight slowly.
- Isometric: the muscle contracts without changing length, so there is no movement, such as holding a plank.
Muscle fibre types
- Type I (slow twitch) fibres contract slowly and resist fatigue: they suit endurance events such as a marathon.
- Type IIa (fast twitch) fibres are fast but fairly resistant to fatigue: they suit events such as the 800 m.
- Type IIx (fast twitch) fibres contract very fast and powerfully but tire quickly: they suit sprints and jumps.
Key terms
- Agonist
- The muscle that contracts to cause a movement (the prime mover).
- Antagonist
- The muscle that relaxes to allow the movement.
- Fixator
- A muscle that stabilises the agonist's origin.
- Antagonistic pair
- Two muscles that work together, one contracting as the other relaxes.
- Isotonic contraction
- A contraction where the muscle changes length and causes movement.
- Isometric contraction
- A contraction where the muscle stays the same length.
- Concentric contraction
- The muscle shortens as it contracts.
- Eccentric contraction
- The muscle lengthens while under tension.