I work out with a speed bag and a heavy bag on my cardio days. I was wondering if these workouts will have an affect on my rest days from weight lifting. Sometimes my biceps and shoulders get tired from the boxing routine, and only the day before I was doing my normal weightlifting routine. Is this a bad thing?

Do you lift on a split schedule or full body each session? If you have a split, it might be advisable to work it so that bicep/shoulder day is at least one day removed from boxing days. Or if it isn't affecting your performance, I wouldn't worry about it too much. Just be cautious of over training.

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Keep your body lean, your blood clean and your mind sharp. -Rollins

I do a split routine, and to be honest it never really affects my actual workout, but I was concerned that it might be affecting my rest time. I'll try and make sure it is one day removed, thanks for the advice.