Side strain is a clinical diagnosis characterized by sudden onset of pain and point tenderness over the rib cage.

This is not an uncommon injury amongst swimmers, tennis players, cricket players and javelin throwers, and can be caused by many other activities, and even from severe coughing.

Magnetic resonance imaging (MRI) has shown that side strain is believed to be caused by a tear of the internal oblique muscle from where it inserts into the undersurface of the ninth, 10th, or 11th rib.

The internal oblique muscle forms part of the superficial covering of the anterolateral abdominal wall. It is one of three large flat muscles in this region that lie under cover of the external oblique muscle.

The mechanism of injury for internal oblique muscle strain is sudden eccentric contraction of the muscle fibers, making it vulnerable to rupture.

Clinically, first aid for muscle injuries follows the RICE (Rest, Ice, Compression and Elevation) principle. The objective of RICE is to stop the injury-induced bleeding into the muscle tissue and thereby minimize the extent of the injury. Rest period is dependent on severity of injury and other factors such as necessary daily activity that may still be exerting strain on the injured area.

The treatment of injured muscle should be carried out by immediate immobilization of the injured muscle. However, the duration of immobilization should be limited to a period sufficient to produce a scar of sufficient strength to bear the forces induced by remobilization without re-rupture and the return to activity should then be started gradually within the limits of pain.

Early return to activity is needed to optimize the regeneration of healing muscle and recovery of the flexibility and strength of the injured muscle to pre-injury levels. The rehabilitation program should be built around progressive agility and trunk stabilization exercises, as these exercises seem to yield better outcome for injured muscle than programs based exclusively on stretching and strengthening of the injured muscle.

Arnica granules can be taken, and arnica oil/gel can also be applied to the injured area to facilitate healing of the injured muscle.

Natural anti inflammatories include capsicum, bromelain, ginger and curcumin.
References:
1. Järvinen TA, Järvinen TL, Kääriäinen M, Aärimaa V, Vaittinen S, Kalimo H, Järvinen M. Muscle injuries: optimising recovery. Best Pract Res Clin Rheumatol. 2007 Apr;21(2):317-31. PMID: 17512485.
2. Hillenbrand A, Henne-Bruns D, Wurl P. Cough induced rib fracture, rupture of the diaphragm and abdominal herniation. World J Emerg Surg. 2006 Nov 24;1:34. PMID: 17125506.
3. Connell DA, Jhamb A, James T. Side strain: a tear of internal oblique musculature. AJR Am J Roentgenol. 2003 Dec;181(6):1511-7. PMID: 14627566.