Strength training cures mouse arm and tennis elbow
Millions of people suffer from chronic pain in their lower arm. Having to make repetitive rotations of their wrist for their work has given them a mouse arm or tennis elbow. Danish researchers at the National Research Centre for the Working Environment discovered that strength-training really helps get rid of these problems.
Computer related injury

About four percent of everyone whose work involves sitting at a computer [Occup Environ Med. 2003 Nov; 60(11): e14.] and eight percent of factory workers [Arthritis Rheum. 2003 Aug 15; 49(4): 519-25.] develop lower arm injuries. The more monotonous the work and the more stress it involves, the greater the likelihood of injury.
The Danes had already discovered that workers with chronic neck pain have an unusual type of fibre in their sore muscles: an unusually large, slow muscle fibre type that does not have a good blood supply. [Pain. 2008 Oct 31; 139(3): 588-93.] This kind of muscle fibre seems to develop as a result of overload and causes pain. Strength training can help develop a healthier form of muscle fibre and thus reduce pain, the Danes theorised.Study
They did an experiment to test this with 282 production workers. The test subjects did work that involved continuous data input on the computer or monotonous mechanical operations, and all had either a mouse arm or tennis elbow.

The researchers got the injured workers to train for three times a week for 20 weeks. Each session lasted 20 minutes. The subjects did wrist-extensions, lateral-raises, front-raises, shrugs and reverse-flies. A control group of 255 injured workers did no training.
The figure below shows that the pain in the subjects' forearms – measured on a scale from 0 [no pain] to 100 [maximum pain] – gradually decreased during the 20 weeks of strength training.

The weights the subjects trained with doubled as the training period elapsed. The subjects therefore gained strength and as a result their muscles and joints incurred less strain, the Danes reason.
Among the workers who had serious pain, the strength training increased the chance of recovery by a factor of 4 to 6.
BMJ Open. 2012 Feb 13;2(1):e000412.