Days after the tragic death of Dave Goldberg, husband of businesswoman and author Sheryl Sandberg, we found out the cause: brain injury that resulted when he fell off a treadmill. Whether there might have been some underlying health issue is the subject of speculation, but one thing's for certain: middle-aged gym goers are rattled. This Q&A should serve to quell anxiety, as it explains the rarity of accidents such as Goldberg's, and asserts that, even though heart attacks are more likely to happen during periods of exercise than inactivity, exercise is crucial to maintaining cardiovascular health. It's likely this terrible accident just boils down to bad luck. Our hearts and sympathies go out to them during this difficult time.