Muscles and Movement 2 - Muscle strength and Force Generation

Muscle Mechanics

  • muscle mechanics describe how muscles move loads and how the anatomical relationship between muscles and bones maximises the work the muscles can do

  • to move an object (i.e. the load) the sacromeres in the muscle fibres need to shorten. the force generated by the contraction of the muscle

  • In Vertebrates muscles are connected to bone via tendons - these move the bones when the muscle contracts

  • Some invertebrates make use of hydrostatic skeletons (e.g.) worms or have an exoskeleton that the muscles are attached to (e.g. arthropods)

Muscle Strength and Endurance - definitions

  • Muscle Strength (Force) = the greatest amount of force that muscles can produce in a single maximal effort

  • Muscle Power = the product of muscle force and contraction velocity - Strength is the ability to exert force, Power is the ability to exert force rapidly

  • Muscle Endurance = ability of a given muscle to exert force against a load, consistent and repetitive

  • Muscles can only pull and always work in Antagonistic Pairs, this means when one muscle pulls up another muscle will pull away

Muscle Energy Supply

Muscles have three systems for supplying ATP for contractions, these are:

  • Immediate system - uses preformed ATP and creatine Phosphate

  • Glycolytic system - metabolizes carbohydrates to lactate and pyruvate

  • Oxidative System - Metabolizes carbohydrates or fats to H2O and CO2

Energy demand in the skeletal muscles come from…

  • ATP is hydrolysed for ion transport

  • Chemo-mechanical transduction of the myosin-actin interaction (Myosis ATPase)

Muscle Fatigue

Muscle fatigue is a reversible condition in which an exercising muscle is no longer able to generate or sustain the expected power output, this can occur at various stages and fatigue is affected by:

  • intensity and duration of contractile activity

  • use of aerobic or anaerobic metabolism

  • composition of muscle

  • fitness level

Several factors can affect muscle tension and strength. They can be grouped into four categories which are Neurological, Muscle strength/Composition and Biomechanical factors.

  • Firing rate of motor Neurons

  • Motor unit recruitment

  • Muscle length-tension relationship

  • muscle fibre type

  • muscle cross sectional area

  • Pennation Angle

  • Joint angle Leverage

  • Muscle Insertion point

Neurological Factors - Skeletal Muscle Twitch

A muscle twitch is the minimum unit of contraction in skeletal muscle and comprises of a single contraction-relaxation cycle in a skeletal muscle fibre

  • a single action potential generates a single twitch

  • A twitch is measured in terms of tension or the amount of force it generates