In the past, I avoided upper body strength training. Why build up extra weight when we don’t need strength in our arms. But upper body strength is important for trail running. This is especially true for running uphill and technical sections. Your trunk and arms act as a counterbalance to your legs and provide much needed power transfer through your core to your legs.
The two best exercises for upper body strength for runners are push ups and chin ups. Push ups are pretty straight forward, but when I first started doing chin ups, I struggled because of my lack of upper body strength. I started out using bands and slowly built my way up to being able to do at least 10 without assistance. This is a great progression to work on over the winter. Watch this Video from Competitor to learn the correct way to get started.