Muscle glycogen is a glucose polymer that is stored in muscle cells. When you exercise, particularly at high intensities, it's the primary substrate used to create ATP. Maintaining or preserving glycogen stores can delay fatigue and even preserve economy.
Given glycogen's positive relationship to endurance performance, athletes and coaches often employ tapers in an attempt to maximize glycogen stores prior to competitions. But as Costill et al. noted back in 1990, glycogen resynthesis may be inhibited following muscle-damaging eccentric exercise.
Eccentric exercise is any exercise that involves "active lengthening" of muscle fibers. Sports that include running, and jumping are eccentric dependent. With running - every footstrike requires absorbing an impact through active lengthening of muscle fibers. That lengthening action can damage the muscle. And little by little, as your run progresses, you accumulate more and more muscle damage. It's not necessarily a bad thing - the muscle will repair itself. But the damage may be evident when you're sore the next day. This damage and the subsequent inflammation may inhibit glycogen resynthesis.
When compared to running, cycling and swimming do not rely nearly as heavily on eccentric muscle contractions. That's one reason why cyclists spend so much time on their bikes - fewer eccentric contractions, less muscle damage, less soreness...
So then, how could this knowledge of muscle damage and glycogen resynthesis impact how the runner, cyclist, and multisport athlete approaches a taper?
Perhaps the runner should take a longer or more aggressive taper than the cyclist. This way, the runner would incur less muscle damage as the important competition approaches - ensuring that glycogen resynthesis is not negatively impacted. And the multisport athlete may want to reduce running volume more aggressively than his/her cycling and swimming volume.
If you're interested in reading more about glycogen resynthesis, I recommend you check out this review by Burke et al.