If you practise Ashtanga, or any other form of vinyasa yoga, Chaturanga is repeated many times. This asana strengthens the chest muscles and Latissimus Dorsi considerably, and many teachers tell students that shoulders and elbows must be in a straight line to protect the Rotator cuff muscles of the shoulder.
Shoulders are highly mobile joints with many muscles acting to cause movements. The main problems that tend to develop are due to the fact that external rotation of the shoulder is caused by three small muscles on the outside of the scapula, whereas internal rotation is caused by one small muscle on the inside of the scapula, but is also assisted by the very powerful Pectoral and Latissimus Dorsi muscles.
Muscle strength imbalances between internal and external rotation develop very easily with Chaturanga, and if bound asanas (which stretch out the chest muscles) are not practised regularly, shoulder problems become worse. Stretching the chest is important, but strengthening the rotator-cuff muscles is often overlooked.
Strengthening the external rotators and balancing them with internal rotation can be helped by regular practise of Vasistasana, however, if you do a lot of Chaturanga and arm balances, doing Vasistasana once on each side is unlikely to be enough, especially if you have already developed rotator cuff problems, or have an existing injury.
Physiotherapists usually prescribe external rotation exercises in varying planes and angles to rebalance the shoulder muscles and chest muscles. Internal rotation is generally not necessary, because it is strong enough already. High numbers of repetitions with small weights are used to build endurance in the external rotators.
Rotation exercises can be done to work with existing injury, but it may be wise to do them anyway, to prevent injury, and some people find that their shoulder flexibility improves tremendously by doing external rotation exercise.
Small weights or resistance bands are used, 0.5kg is a good place to start, it’s unwise to exceed 2kg. Instead of splashing out on a set of weights, water bottles in 0.5 or 1 litre sizes work very well. Many sets of 15-20 repetitions are done to strengthen shoulder rotator-cuff muscles.
Ellenbecker, De Carlo, DeRosa, 2009, Effective Functional Progressions in Sport Rehabilitation
Brunnstrom’s Clinical Kinesiology, 5th Ed, 1996