The time-courses of satellite cell (SC) activation and protein expression of hepatocyte growth factor (HGF), HGF activator (HGFA), HGFA inhibitor-1 (HAI-1), and HGFA inhibitor-2 (HAI-2) in human skeletal muscle, as well as serum HGF following a single bout of muscle lengthening contractions, were determined. Eight recreationally active participants were recruited for the study. Subjects performed 300 lengthening contractions involving the quadriceps femoris muscles of a single leg at a fixed velocity of 180 degrees/s. Percutaneous muscle biopsies were taken before (PRE) and at 4 h (T4), 24 h (T24), 72 h (T72), and 120 h (T120) following the exercise. The protocol resulted in an increase in the number of SCs [neural cell adhesion molecule (NCAM)-labeled cells] expressed relative to total myonuclei, at T24, compared with both PRE and T4 (P<0.05), and peaked at T72 (approximately 80% increase vs. PRE, P<0.05). HGF protein increased significantly in serum from baseline (PRE) to T4 (P<0.05). Active HGF protein was detected in skeletal muscle at rest [14.4+/-1.3 average integrated density value (IDV)/actin average IDV] and tended to increase at early time-points (P=0.12). HGFA protein increased significantly from PRE to T24 (P<0.05). HAI-1 protein increased significantly from PRE to T24 (P<0.05). HAI-2 (32 kDa) increased significantly from baseline (PRE) by T24 (P<0.05), and also by T72 and T120 (P<0.05). We conclude that a single bout of lengthening muscle contractions is sufficient to activate SCs, which may involve both a local and systemic HGF response to contraction-induced injury.