The purpose of this study is to determine the optimal time interval between light emitting diode application and exercise to improve fatigue resistance.The results of this study could be useful in planning a rehabilitation program in musculature disorders and also in athletic training.

1. To determine the effect of light emitting diode applied 5 minutes before exercise on pain, rate of perceived exertion and maximum voluntary contraction.
2. To determine the effect of light emitting diode applied 1 hour before exercise on pain, rate of perceived exertion and maximum voluntary contraction.
3. To determine the effect of light emitting diode applied 5 hours before exercise on pain, rate of perceived exertion and maximum voluntary contraction.
4. To determine the difference between light emitting diode applied 5 minutes,1 hour or 5 hours before exercise on pain, rate of perceived exertion and maximum voluntary contraction.

Inclusion Criteria:

• Healthy non athletics subjects.
• Age ranges from 20-40 years.
• Body mass index is less than 25 kg/m 2

Exclusion Criteria:

• Neurological deficit and recent injury to either upper extremity
• non diagnosed pain .
• Contraindications to LED irradiation (such as light hypersensitivity, fluctuating blood pressure, insufficient blood circulation, fever and inflammation of the skin)
• Conditions in which physical exertion is contraindicated (such as cardiovascular deficits, hypertension and respiratory problems)
• Restriction in shoulder or elbow range of motion;
• Neoplasm,
• Rheumatoid,
• Strength training in the past 6 months;
• Previous surgery in the spine or upper extremity;
• Complaints of pain in the shoulder, elbow,wrist, and trunk musculature system;
• Use of dietary supplements; and not in any other exercise program for at least the past 3 months.