To determine whether anterior knee pain (AKP), during running, acutely affects lower-extremity electromyography (EMG) and articular cartilage metabolism.
A within-subjects design was used. Each of 12 able-bodied subjects ran on a treadmill for 30 min for three different sessions: control (no infusion), sham (0.9% NaCl infusion into the involved-leg infrapatellar fat pad), and pain (5.0% NaCl infusion into the involved-leg infrapatellar fat pad). Bilateral surface EMG was monitored for the vastus medialis (VM), vastus lateralis (VL), and gastrocnemius (GA). Serum cartilage oligomeric matrix protein (COMP) concentration was determined before, after, and 60 min after the run. A functional analysis approach was used to compare EMG amplitude, across the entire stance phase, between sessions and legs. Mixed-model analysis of covariance was used to compare serum COMP concentration between sessions, across time.
Relative to the uninvolved leg, greater involved-leg VL and GA EMG amplitude existed during midstance for the sham and control sessions (P < 0.01). During the painful session, however, involved-leg VM, VL, and GA EMG amplitude was 5-10% less than for the uninvolved leg. COMP concentration immediately post-run was 14% and 21% greater than pre-run (P = 0.01) and 60 min post-run concentrations (P < 0.01), respectively. Session, however, did not significantly influence COMP.
During a 30-min run, AKP acutely alters midstance VM, VL, and GA EMG amplitude. AKP during a 30-min run does not, however, acutely influence articular cartilage metabolism.