Warmed muscles are more efficient, strong, and resilient. Muscle speed and efficiency are enhanced by a rise in the temperature in the muscle. Muscles that are overused, fatigued, and under-conditioned are more tense and require more work for a demanding task. An athlete wouldn’t think of starting in without a warm up!
It is important to start by gently and smoothly using your muscles for a few minutes to increase blood flow without stressing them. Cold muscles are inelastic!
First, warm up away from the instrument. Any aerobic activity like a brisk 5-minute walk, stair-climbing, or jumping jacks followed by some upper extremity stretching will do the trick. These could include shoulder shrugs and rolls, reaching towards the ceiling, stretching your arms back behind you, clasping your hands and lifting your arms behind you, and some hand and arm circles— all good for warming up.
At the instrument, start slowly and easily in the medium range of your instrument and at a medium tempo and dynamic. Avoid starting with chop-busting exercises, double stops, large chords, any reaches, and other pyrotechnics. How you start playing is more important than what you play. Working a muscle too quickly can cause the muscle to contract. Start gently and gradually increase the speed and intensity in each session. Take more time to warm up when it’s cold outside, when you are more fatigued, and especially after injury. Remember to keep breathing and to focus on the release of any awkward or strenuous positions.
From Janet Horvath’s Playing (less) Hurt; An Injury Prevention Guide for Musicians