Mouse shoulder: a painful ailment for PC gamers

What is mouse shoulder?

Mouse shoulder is an ailment that occurs in the proximal (closer to the center of the body) tendon attachment of the long head of the biceps [brachii] muscle. The biceps muscle is involved in both elbow and shoulder flexion. As the name suggests, PC gamers are more likely to experience this injury due to the use of the mouse.

Due to misuse and imbalance, the fiber orientation of the tendon becomes disrupted. This dysfunction is called a tendinopathy, which is different than tendinitis—a common misnomer for this condition. We discuss this difference in more detail in the Pathophysiology section below.

Pertinent anatomy

It’s important to know some basic anatomy of the shoulder to understand mouse shoulder. To begin, the tendon affected in mouse shoulder is the proximal tendon of the long head of the biceps muscle.

The biceps muscle has two parts (bi- meaning two):

• Long head: the longer of the two parts of the biceps muscle runs in front of the shoulder and attaches just above the shoulder joint on the scapula (shoulder blade)

• Short head: the shorter part of the biceps muscle also attaches the the scapula, but this attachment site is further inwards and below the clavicle (collar bone)

On the distal end (further away from the center of the body), the two parts of the biceps muscle converge and attach to the radius—the bone on the thumb side of your forearm.

Pathophysiology

This injury is a tendinopathy! It is NOT inflammatory in nature, and the term tendinitis is not appropriate! This is critical to determine the appropriate prevention and rehabilitation.

Mouse shoulder occurs when there is at least one of two imbalances in muscle contraction. If one or both of these imbalances occur over time, degeneration of collagen (the protein found in connective tissue) occurs. This leads to the disruption of the tendon fiber orientation in the the biceps tendon.

The strong fibers of a tendon should line up parallel with one another. In tendinopathy, these fibers will become jumbled or disorganized—commonly described as adhesion formation—causing pain and affecting the movement of the tendon and the shoulder joint.

• Concentric vs. eccentric imbalance
  • Concentric: the shortening phase of a muscle contraction
    • PC gamers: lifting the arm forwards and upwards to grab the mouse is a concentric action that includes the biceps muscle
    • Weight lifting example: the up-phase of a biceps curl (raising the dumbbell up to your shoulder)
  • Eccentric: the lengthening phase of a muscle contraction
    • In gaming, there is no instance of an eccentric contraction, and this is the problem!
    • Weight lifting example: the down-phase of a biceps curl (controlled lowering of a dumbbell back to your hip)

• Agonist vs. antagonist imbalance
  • Agonist: the active muscle during a particular movement
    • PC gamers: the agonist muscles are the ones involved in shoulder flexion; this includes the biceps muscle
  • Antagonist: the muscle that opposes the agonist; this muscle (or group of muscles) will be relaxed during agonist contraction
    • PC gamers: the antagonist muscles are ones involved in shoulder extension; these include the latissimus dorsi and posterior deltoid; these muscles are not challenged with any significant resistance during PC gaming

For console gamers, these imbalances are not pertinent for mouse shoulder. The imbalances in console gaming are more likely to lead to medial epicondylosis or gamer’s thumb.

Concentric vs. eccentric imbalance

When concentric contractions occur too frequently without the counterbalance of eccentric contraction, collagen begins to degenerate from the chronic shortening. Eccentric contraction—the lengthening of a muscle and tendon under tension—helps maintain the tendon fiber orientation.

Mechanical loading, particularly in the eccentric phase, protects tendons from injury!

Agonist vs. antagonist imbalance

When agonist muscle actions occur too frequently without the counterbalance of their antagonist, there is imbalance in the strength and tension on the joints involved. When strength and tension are not balanced, the muscles can be overworked and injury becomes more common.

The concentric vs. eccentric imbalance is usually the direct cause of any tendinopathy, but the agonist vs. antagonist imbalance may exacerbate the ailment and prolong healing time.

Signs and symptoms

If you’re affected by mouse shoulder, you’re likely to experience the following symptoms:

• Pain
  • Most often, you will experience pain in the front portion of the shoulder and upper arm
  • Forward and upward movements of the shoulder joint may increase pain; for example, pushing forward or lifting overhead
  • Reaching your arm backwards may be uncomfortable due to stretching of the biceps tendon

• Weakness
  • Pushing or overhead movements may feel weak; however, your perceived weakness is more likely due to pain rather than true muscle weakness

Other common findings may include:

• More pronounced symptoms with flexion of the shoulder joint (e.g., using a mouse)
• Worsening symptoms following periods of rest
• Relief or improvement of symptoms after warming up the shoulder

Note: Mouse shoulder is considered a tendinopathy, and inflammation will not be present. Inflammation is categorized by pain with accompanying swelling, redness, and heat (feeling warm to the touch).

If you notice these signs of inflammation, you are experiencing something different than simple mouse shoulder tendinopathy. You should consult your doctor if you are concerned about these symptoms.

Common mechanism(s) of injury

For gamers, mouse shoulder is more common for PC users due to lifting the arm or holding the arm up to use the mouse. Common risks for PC users include:

• Poor chair or desk setup
  • If your desk is too high, you will need to elevate your arm further to reach the mouse
  • Likewise, if your chair is too low, the same issue occurs

• Lack of eccentric contraction
  • As described in Pathophysiology above, the actions performed in PC gaming do not include eccentric contraction, or lengthening of the extensor muscles
  • The imbalance of muscle shortening without lengthening under tension leads to tendon fiber disruption

• Lack of antagonist muscle contraction
  • Also described in Pathophysiology above, it is unlikely that you perform pulling or rowing actions during gaming
  • The lack of forceful shoulder extension allows for over-activity of the shoulder flexor muscles (including the biceps), perpetuating the shortening and fiber disruption of the tendon

Prevention

The most common mechanisms of injury for mouse shoulder are imbalances—both in movement and in body positioning (posture and ergonomics). Therefore, correcting your posture and balancing both muscle contraction and activation are simple, yet extremely effective preventative measures.

In addition to these mouse shoulder-specific preventative measures, be sure to take breaks to help prevent overuse tendinopathy.

Concentric vs. eccentric muscle contraction

The lengthening phase of muscle contraction is the most important! Below, we have a list of exercises that may help resolve this ailment. It is absolutely essential to perform the eccentric, or “down-phase” portion of these exercises slowly and under control!

Resisted exercises to add eccentric action to the biceps muscle include:

Supinated front raise

For the following exercise, use both arms to lift the weight and only one arm (the affected side) to lower the weight back down.

1. Use a dumbbell or small weighted object
2. Using BOTH arms, lift the dumbbell or weight directly in front of you, up to shoulder height
3. With the affected side, only: keep your palm face up and your elbow straight. SLOWLY, and under control, return the weight to the starting position
4. Repeat steps 2-3 for a total of 3 sets of 8 repetitions

(Incline) biceps curl

Perform this exercise on an incline bench, if possible, to further stretch your biceps tendon. The incline should be approximately 45 to 60 degrees. If you don’t have an incline bench, standing or sitting upright is still useful.

1. Hold a dumbbell or small weighted object in your hand
2. Keeping your palm face up, bend your elbow to curl the dumbbell upward to your shoulder
3. SLOWLY, and under control, return to the starting position
4. Repeat steps 2-3 for a total of fifteen (15) repetitions

Agonist vs. antagonist muscle activity

Balancing the muscle activity at any joint will help keep all the mechanical structures healthy. For PC gamers, flexion of the shoulder is the strenuous action; therefore, it is important to perform extension exercises and stretches for the shoulder.

Shoulder extension exercises and stretches include:

Resisted row

1. With dumbbells or a barbell, bend forward so your chest is facing the ground
2. Start with your arms hanging straight in front of you, and pull the weight towards your belly
3. Slowly return the weight back downward to the starting position
4. Repeat steps 2 and 3 for a total of fifteen (15) repetitions

Sleeper stretch

1. Lie on your side with your arm 90 degrees from your trunk and your elbow bent 90 degrees
2. With your other arm, press your forearm down towards the surface you’re lying on; you should feel the stretch in the back of your shoulder
3. Hold this stretch for 10 seconds
4. Perform this stretch 3 times

Rehabilitation

To effectively resolve mouse shoulder, it is important to first identify and correct the initial cause. For example, if your body is in poor position while gaming or you’re not performing the eccentric action of the biceps muscles outside of gaming, protocols may be ineffective because of the constant exacerbation.

Step 1: aggressive cross-friction massage

The provider should use a firm surface (thumb pressure or a knuckle, for example) to apply moderate pressure to the biceps tendon and scrape perpendicularly across the tendon. Unfortunately, this maneuver tends to be moderately painful.

This will loosen the tendon matrix and make it more malleable for the next part of the treatment.

Step 2: Hypervolt+

When compared to their muscles, tendons have approximately 7.5x less oxygen consumption due to limited blood flow, and this is one reason why tendons heal more slowly.

In order for your body to heal any tissue, blood is required to remove toxins and cellular waste, to bring oxygen into the working cells, and to provide nutrients (in other words, building materials) to the damaged tissue.

The Hypervolt+® tool was added at this step to stimulate all the soft tissue in the region of the affected tendon to increase blood flow. With increased blood flow comes increased oxygen and nutrients to enhance healing; there will also be more rapid removal of toxins from the healing process.

Step 3: heavy eccentric loading

Following cross-friction to loosen the tendon matrix, resistance must be added to lengthen the tendon under tension. This resistance should be moderate-to-significantly heavy in order to properly pull the tendon fibers taut.

For mouse shoulder, the best exercise is an incline dumbbell curl. The provider should place the weight in the patient’s hand with the elbow flexed, and the patient resists the weight downward to pull the tendon.

Step 4: continued blood perfusion via heat therapy

Using heat packs or other heat therapies (e.g., infrared laser) on the affected area should conclude this protocol. Generally, a heat pack should be used for 10-15 minutes. Adding a damp towel between the heat pack and the affected area will increase its effectiveness by creating moisture that penetrates further into the body.

Generally, people think to ice their ailments to relieve the pain. However, ice relieves inflammation, and as previously discussed, inflammation is not the cause of pain. Therefore, ice would not help this condition. In fact, icing the affected area may prolong the healing process.

Heating the area increases blood flow, thereby increasing oxygen and nutrients needed for recovery. For an overuse tendinopathy, heat is more helpful than ice. Following resolution, continuation of these protocols allows for prevention of this condition from reoccurring.

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