The erector spinae is the muscle you are looking for, however is should be noted that technically this is a large group of muscles.
latissimus dorsi
It is actually a lower back muscle that is located in the posterior abdominal wall
The pectoral and deltoid muscles are often helped by using a muscle vest although some users say that their lower lumbar back muscles are also helped by it.
Calves are located in the back of your feet.
Trapezius Muscle!
The largest muscle of your calf is the gastrocnemius.
latissimus dorsi pulls inferiorly, the lower trapezius pull back. Depends on the movement.
Lower back
There are a few reasons why you might have twinges in your lower back. You could have a pulled muscle.
the gluteus maximusLatissimus dorsiThe Latissimus Dorsi is the most superficial muscle of the lower backlatissimus dorsi
sure
Avoid using it until it heals.
This muscle is found in the lower part of the leg
You could have strained or pulled a muscle.
Many things can cause lower back pain such as a pulled muscle or even a kidney infection.
If you have a twitch on the left lower back, it might be a muscle spasm or even a pinched nerve. This could also be related to vertebral damage or back spasms in the muscles.
it could be that the person has back spasm
The bulkiest would be the glutenous maximus. the main "butt" muscle. the largest surface area would be the latimus Dosi "lower back" muscle .