The most likely reason your bicep hurts when you put your arm behind your back is due to biceps tendinitis or another form of strain or impingement affecting the bicep tendon. Reaching behind your back stretches and potentially compresses the bicep tendon, exacerbating any existing inflammation or injury.
Here's a more detailed breakdown:
1. Biceps Tendinitis:
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What it is: Biceps tendinitis is inflammation or irritation of the biceps tendon, which connects the biceps muscle to the shoulder and elbow.
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Why it hurts: When you reach behind your back, the bicep tendon is stretched and potentially compressed, irritating the inflamed tendon. This can cause pain at the front of the shoulder, which may radiate down the arm.
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Symptoms (aside from pain when reaching behind the back):
- Sharp pain in the front of your shoulder when reaching overhead or across your body.
- Tenderness to touch in the front of your shoulder.
- Pain that may radiate toward the neck or down the front of the arm.
2. Biceps Strain/Muscle Injury:
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What it is: A bicep strain is a tear or overstretch of the bicep muscle fibers.
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Why it hurts: Reaching behind your back can further stretch the injured muscle, causing pain.
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Causes: Overuse, improper lifting technique, or sudden movements.
3. Shoulder Impingement:
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What it is: Shoulder impingement occurs when the tendons of the rotator cuff muscles become compressed or pinched in the shoulder joint. This can also affect the biceps tendon if it becomes involved.
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Why it hurts: Reaching behind your back can narrow the space where the tendons pass, increasing the impingement and causing pain.
4. Other Potential Causes:
- Referred Pain: Pain originating from another area, such as the neck or shoulder, can sometimes be felt in the bicep.
- Underlying Shoulder Conditions: Arthritis or other joint problems in the shoulder can contribute to bicep pain, especially with specific movements.
What to Do:
- Rest: Avoid activities that aggravate the pain.
- Ice: Apply ice to the affected area for 15-20 minutes several times a day.
- Over-the-Counter Pain Relievers: Ibuprofen or naproxen can help reduce pain and inflammation.
- See a Doctor: If the pain is severe, persistent, or accompanied by other symptoms such as weakness or numbness, consult a doctor or physical therapist for diagnosis and treatment. They may recommend physical therapy, injections, or, in rare cases, surgery.
