Unlock this article and unwrap savings this holiday season. Already have an Outside Account? Sign in Now 30% Off. $4.99/month $3.49/month* Get the one subscription to fuel all your adventures. Map your next adventure with our premium GPS apps: Gaia GPS Premium and Trailforks Pro. Read unlimited digital content from 15+ brands, including Outside Magazine, Triathlete, Ski, Trail Runner, and VeloNews. Watch 600+ hours of endurance challenges, cycling and skiing action, and travel documentaries. Learn from the pros with expert-led online courses. Join Outside+ *Outside memberships are billed annually. You may cancel your membership at anytime, but no refunds will be issued for payments already made. Upon cancellation, you will have access to your membership through the end of your paid year. More Details Backpacker Videos Video loading... Alpine Fitness Alpine Fitness: Core Strength for Backpackers Share this Facebook Icon Twitter Icon Email Icon Join Backpacker Create a personalized feed and bookmark your favorites. Join for free Already have an account? Sign In Join Backpacker Create a personalized feed and bookmark your favorites. Join for free Already have an account? Sign In These three exercises will strengthen your core for long days on the trail with a heavy pack.