Shoulder flexibility is usually very difficult for men to achieve. Unlike with hips, male and female shoulder structure differs only in size, and women mostly struggle to develop upper body strength, while men cannot get their elbows behind their ears. Strong women usually have similar inflexibilities to men and this is often related to differences in strength between chest muscles, Latissimus Dorsi and the rotator cuff, as well as posture.
Vinyasa yoga is often blamed for shoulder injury. Vinyasa takes the shoulder through a range of movements, as well as lengthening the Latissimus Dorsi in Adho Mukha Svanasana. Lats, like chest muscles, are internal rotators of the upper arm and are large and powerful muscles, whereas the rotator cuff muscles are mainly responsible for external rotation and are much smaller muscles. Chaturanga strengthens the chest and a strength imbalance tends to develop. Even if you never have a rotator cuff injury from vinyasa practice, shoulders can become too tight to do asanas like Viparita Dandasana and Kapotasana.
Bound asanas are thus very important because they lengthen the chest muscles, that’s why there are plenty of them in Ashtanga practice, and they should never be neglected in any vinyasa practice. Other asanas important for shoulder health are Purvottanasana, Vasistasana, Pincha Mayurasana, Sirsasana and Urdhva Dhanurasana. Shoulders need to be strengthened in a variety of directions in every practice, both to avoid injury and improve flexibility.
For some, flexibility in the shoulder only improves if the rotator cuff is strengthened in external rotation. The shoulder joint is the most mobile joint in the body but for the same reason is extremely vulnerable to injury and stretches should never be forced. Stretching the chest and Lats is a much more effective way to improve shoulder mobility anyway, and these large muscles are not easily damaged by stretching. Chest muscle fibres run in a number of different directions and stretching needs to have the arm in a variety of positions, for example, Purvottanasana and Urdhva Dhanurasana, as well as bound asanas.
A rounded upper back can also make the shoulders inflexible and prone to injury and the causes of the rounding of the upper back need to be assessed. These issues are often complex and can be related to the hips and are best treated by a professional, especially if the person has practiced yoga for a long time and there is no improvement in the upper back.
Ellenbecker, De Carlo, DeRosa, 2009, Effective Functional progressions in Sport Rehabilitation
Sharkey, 2008, The Concise Book of Neuromuscular Therapy
Kendall, McCreary, Provance, 1993, Muscles, Testing and Function