The body heals and recovers with rest. If listening to calming music or certain frequencies allows you to do this, then yes they will help in that manner. As far as a healing frequency for muscles? You might be referring to EMS, which is electrical stimulation through the use of patterns and intensity to encourage blood flow, light muscle contractions and nerve excitement. As a Physical therapist, I often use this in the early stages of rehab to acute injuries or to help with repetitive chronic issues such as tendinopathy or muscle overusage.