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•  Movement of the body requires muscles to work in antagonistic pairs

Muscles connect to bones (via tendons) and contract to provide the force required to produce movement

  • The muscle connects a static bone (point of origin) to a moving bone (point of insertion)

Skeletal muscles exist in antagonistic pairs (when one contracts, the other relaxes) to enable opposing movements 

  • Opposing movements may include: flexion vs extension, abduction vs adduction, protraction vs retraction, etc.

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•  Antagonistic pairs of muscles in an insect leg

Many types of insects (including grasshoppers and praying mantises) have hind legs that are specialised for jumping

  • The jointed exoskeleton of the hind leg is divided into three parts: femur (upper leg), tibia (middle leg) and tarsus (lower leg)
  • The femur and tibia are connected by two antagonistic muscles: flexor tibiae muscle and extensor tibiae muscle

When the flexor muscle contracts, the extensor muscle relaxes and the tibia and femur are brought closer together

  • This retracts the hind quarters in preparation for pushing off the ground

When the extensor muscle contracts, the flexor muscle relaxes and the tibia is pushed away from the femur

  • This extends the hind quarters and causes the insect to jump

Antagonistic Muscle Pairs in an Insect Leg

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Jumping Motion of a Praying Mantis

Video courtesy of Burrows et al. (Current Biology, 2015)