relax
When one muscle in a pair contracts the other expands.
Relaxes
It Contracts
When one muscle in a pair contracts the other expands.
contracts - for antagonistic muscle pairs e.g. muscles in arm (when one relaxes, other contracts, and vice versa)
relax
Relax
When one muscle contracts, the other one expands.
Expand.
the answer is when one muscle contracts the other relaxes
It relaxes
Because muscle cells can only contract, not extend, skeletal muscles most work in pairs. While one muscle contracts, the other muscle in the pair relaxes to its original length.