As you mentioned that guide at gym mentioned about injury at your shoulder , you need to get it treated. If there is pain in your shoulder at rest or particular activities to name a few like if you comb the hair with left hand or may be when you raise your your arm to bolt a door....or specific activities.....a physical examination by physiotherapist is required. Once pain is managed and injury is healed .strengthening exercises have to be done.
Next Steps
visit a physiotherapist for assessment and treatment. you may consult us online or offline at Muskaan Physiotherapy Clinic ,Pushpanjali.
Health Tips
it is not just any exercise but right exercises which are going to improve strength.