Discussion
injuries, pain
SECONDARY
This was the first study to investigate the effects of supplementing with two doses of CP compared to PLA on pain, function, and mental/social as well as physical health-related QOL over 3, 6, and 9 months in middle-aged physically active males and females. The main findings from this study are that significant improvements in ADLs and pain, measured via the KOOS, were observed with 10 g/d of CP supplementation over 6 months, although pain only improved in HF exercisers. Similarly, improvements in the VR-12 mental component scores were observed after supplementing with 10 g/d over 6 and 9 months. Further secondary analyses also demonstrated improvements with 10 g/d of CP over 9 months in females, but not males, and in HF but not in LF exercisers. Lastly, physical components scores of the VR-12 significantly improved with 20 g/d over the course of 9 months in females, but not in males, with no differences in this measure observed between HF and LF exercisers.Our findings of improvements in ADLs and pain are in accordance with prior literature reporting increased return to ADLs, improvements in pain, as well as accelerated return to play after sports related injuries [Akin to studies by Praet et al. (2019) and Bruyère et al. (2012), the current study population reported improvements in the KOOS measure for pain in those exercising at a low to moderate intensity greater than 188 min per week. This indicates that frequent physical activity may moderate the effects of the CP supplementation on pain. The moderating effects of exercise on mitigating pain with CP supplementation may be attributed to increased blood flow and delivery of amino acids and bioactive peptides to the connective tissue during exercise, which is otherwise poorly vascularized [Although effective at 6 months, the benefits of CP supplementation on ADLs and pain measured at 6 months were not present when measured at 9 months. This could be due to fewer participants remaining in the 9-month arm of the study, or to the exclusion of participants in analyses due to injuries. Nevertheless, although not significant, a trend toward a significant group by time interaction with a large effect size in ADLs was observed in HF exercisers at 9 months (Contrary to our other study findings, a treatment by time interaction in QOL scores approached significance with a large effect size in LF but not HF exercisers, from baseline to 9 months (To our knowledge, this is the first study to examine the effects of CP supplementation on the VR-12 and to also find significant improvements in mood with supplementation. Moreover, limited studies have evaluated the impact of CP supplementation on mood or mental health, and those that have, did not yield effects. For example, Clifford et al. (2019) examined the effects of 12 weeks of CP supplementation on the Brief Assessment of Mood Adapted (BAM+) in young recreationally active males and found no significant differences between the CP treatment group and control [Correspondingly, cognitive function and brain structure in humans have also shown to benefit from CP supplementation. In a clinical pilot study, Koizumi et al., (2019) found that CP supplementation of 5 g/d for 4 weeks improved cognitive function and memory, as well as brain structure, measured by fMRI, in healthy participants ages 49 to 63 years [As previously stated, pain-related decreases in function can lead to decrements in mood and mental health, resulting in a cycle of restriction [The second component of the VR-12, the physical component score, is a measure of physical QOL. A significant group by time interaction in physical component scores was observed at 9 months, and although no significant main effects for time were observed between groups in post hoc analyses, females in the 20 g/d group had significant improvements in physical component scores, whereas those in the 10 g/d and PLA groups did not. These findings suggest that the interaction observed in the total sample at 9 months was driven by females and not males, and that 20 g/d over 9 months had a significantly beneficial effect on the VR-12 physical component scores in females.