Muscle diseases are more common than you may think. Often these are typical to breed (eg Polysaccharide Storage Myopathy or PSSM in QHs or Warmbloods). If suspected, your vet can diagnose this.
Tip 4 – As with people, many conditions can be managed with appropriate remedies; whether they be medical and/or natural, a good nutrition program and the right amount and type of exercise (including warm up and cool down). If unsure, seek professional advice.