That's concerning. Note that the treatment group performed ever so slightly better than placebo. I'm guessing that that is either due to random chance, or a benefit that any anti-inflammatory plant may provide.

I'd be curious to know why nettle. The authors of this paper seem to think it is the anti-inflammatory and antioxidant activity. However, they are merely following up on past research. They mention that nettle has been used worldwide as an alternative medicine. Therefore, the original research may be based on the traditional uses of the plant.

If nettle does in fact work, I see three possibilities. Nettle may have unique benefit that this study wasn't powered enough to find. Nettle may may have benefit that any plant anti-inflammatory plant would have. Finally, they may not have been using nettle properly.