| Fourteen college-age recreationally active men (Height: 176.5 ± 6.6 cm, Mass: 79.0 ± 10.8 kg, Rel Fat: 12.0 ± 5%) were paired for activity type and body mass and underwent 40 minutes of downhill running at a moderate decline and intensity [eight five-minute bouts, 55–60% maximal oxygen uptake (VO2max), −8% grade]. For six weeks prior to the run, subjects consumed either conjugated linoleic acid (CLA) (0.15 g/kg per day) or safflower oil placebo (PLB). Subjects consumed a controlled diet based upon their usual intake pre- and post-run. No significant group differences were found regarding total energy, protein, carbohydrate, or fat intake. Significant differences were found for perceived muscular soreness (1.7 ± 0.8 at 48 h post-run vs. 0.4 ± 0.6 at 96 h post-run; p < 0.05) and quadriceps' force output (743 ± 156 at 48 h post-run vs. 812 ± 60 N pre-run; p < 0.05). The run also elevated serum lactate dehydrogenase at 2 h (183.7 ± 22 vs. 156.2 ± 4.8 U/l; p < 0.05) and creatine kinase at 24 h (479 ± 333 vs. 210 ± 42 U/L; p < 0.05). A group by time interaction was found for serum creatine kinase, with CLA subjects exhibiting higher concentrations compared to PLB at 24 hours post-run (643 ± 476 versus 315 ± 191 U/l; p < 0.05). Total white cell count increased significantly at 2 h post-run (7.0 ± 0.6 vs. 5.3 ± 0.6 cells per mm3; p < 0.05) as did neutrophil number (4.7 ± 1.2 vs. 3.0 ± 0.8 cells per mm3; p < 0.05) compared to pre-values. Monocyte percentage gradually increased over the five-day recovery period, reaching significance on day five (10.9 ± 0.4 vs. 8.6 ± 1.1%; p < 0.05). No significant interactions were found regarding leukocytes. No group, time, or group by time interactions were found for 24-hour urinary nitrogen excretion, serum interleukin-6, C-reactive protein, glucose, alanine and aspartate aminotransferase, cortisol or oxygen consumption. In conclusion, downhill running of this intensity and duration does not elicit the full spectrum of acute phase variables seen in clinical settings. Additionally, CLA administration for six weeks increases exercise-induced serum creatine kinase but it cannot mitigate selected physiologic responses associated with this type of downhill run. |
