Experimental protocol for the acute studies. 750 mg 13C-proline and 3250 mg 12C-proline was injected over 3 min. Venous blood samples were drawn at 10- to 30-min intervals after the bolus injection. The tendon fractional synthetic rate (FSR) was measured over a 2 hr-period. Patellar tendon tissue was harvested during the operation. In the exercise group, a 1-hr unilateral exercise bout was completed 24 hours before tendon tissue was harvested.