W. Matt Denning

Ambulation speed and corresponding mechanics are associated with changes in serum cartilage oligomeric matrix protein.

Because serum cartilage oligomeric matrix protein (COMP) has been used to reflect articular cartilage condition, we aimed to identify walking and running mechanics that are associated with changes in serum COMP. Eighteen subjects (9 male, 9 female; age=23 ± 2 yrs.; mass=68.3 ± 9.6 kg; height=1.70 ± 0.08 m) completed 4000 steps on an instrumented treadmill on three separate days. Each day corresponded to a different ambulation speed: slow (preferred walking speed), medium (+50% of slow), and fast (+100% of slow). Synchronized ground reaction force and video data were collected to evaluate walking mechanics. Blood samples were collected pre-, post-, 30-minute post-, and 60-minute post-ambulation to determine serum COMP concentration at these times. Serum COMP increased 29%, 18%, and 5% immediately post ambulation for the fast, medium, and slow sessions (p<0.01). When the speeds were pooled, peak ankle inversion, knee extension, knee abduction, hip flexion, hip extension, and hip abduction moment, and knee flexion angle at impact explained 61.4% of total variance in COMP concentration change (p<0.001). These results indicate that (1) certain joint mechanics are associated with acute change in serum COMP due to ambulation, and (2) increased ambulation speed increases serum COMP concentration.

Effects of Experimental Anterior Knee Pain on Muscle Activation During Landing and Jumping Performed at Various Intensities

CONTEXT Although knee pain is common, some facets of this pain are unclear. The independent effects (ie, independent from other knee injury or pathology) of knee pain on neural activation of lower-extremity muscles during landing and jumping have not been observed. OBJECTIVE To investigate the independent effects of knee pain on lower-extremity muscle (gastrocnemius, vastus medialis, medial hamstrings, gluteus medius, and gluteus maximus) activation amplitude during landing and jumping, performed at 2 different intensities. DESIGN Laboratory-based, pretest, posttest, repeated-measures design, where all subjects performed both data-collection sessions. METHODS Thirteen able-bodied subjects performed 2 different land and jump tasks (forward and lateral) under 2 different conditions (control and pain), at 2 different intensities (high and low). For the pain condition, experimental knee pain was induced via a hypertonic saline injection into the right infrapatellar fat pad. Functional linear models were used to evaluate the influence of experimental knee pain on muscle-activation amplitude throughout the 2 land and jump tasks. RESULTS Experimental knee pain independently altered activation for all of the observed muscles during various parts of the 2 different land and jump tasks. These activation alterations were not consistently influenced by task intensity. CONCLUSION Experimental knee pain alters activation amplitude of various lower-extremity muscles during landing and jumping. The nature of the alteration varies between muscles, intensities, and phases of the movement (ie, landing and jumping). Generally, experimental knee pain inhibits the gastrocnemius, medial hamstring, and gluteus medius during landing while independently increasing activation of the same muscles during jumping.