If you want to increase tendon strength, buy a cheap broom handle, some garden twine and some round weights, the type with a hole in the middle.
Tie the twine round the centre of the broom handle, and holding the handle out in front of you measure off enough twine to reach the ground plus an extra foot.
Cut the twine and tie the loose end around the weight.
Hold the broom handle straight out in front of you and wind it up until the weight reaches the handle, then wind it slowly back down. Repeat until your arms are ready to fall off.