I bought a rower (Concept2) about a month ago with the view of getting my fitness and strength up for the coming MTB season. I've been spending 20 minutes on it every weekday morning before work, doing a combination of distance and intervals. First ride out solo today where I could push myself. I really felt a difference both from a strength and endurance perspective. I was less fatigued which enabled me to think about where I was riding and actually ride lines rather than just bombing through the trails. Rowing is addictive, there's lot of technique involved and you can really tell correct technique by the power you put out, you can see it in the data. Best of all it's non-impact so good for those of us getting older.