At this age, you’re at your physical peak: fast, strong, and quick to recover. That lets you play hard–but without training, you won’t reach your potential or lay a solid foundation for later years. Robert Mazzeo, professor in the Department of Integrative Physiology at the University of Colorado-Boulder, says you only get one shot at making the most of this stage’s "optimal physiological and biochemical adaptations." Start with our age-adapted workout on the last page, then get hiking.
A: Circulatory system Pliable capillaries and cell walls easily transfer nutrients and oxygen from the bloodstream to the muscles and clear away muscle-fatiguing waste. This enables shorter recovery time and powers endurance training. Optimize it: Endurance training (45-60 minutes of cardiovascular exercise at a perceived exertion (PE) of at least 13; see page 49) increases capillary supply to muscles and enhances overall performance.
B: Heart A 20-year-old’s ticker is capable of pumping 10 times the amount of blood needed to preserve life, which means there’s plenty of power to supply muscles with oxygen–even during the toughest climbs. Optimize it: Sustained exercise (long dayhikes) will lower your resting heart rate, the hallmark of well-trained athletes.
C: Lungs The body creates new alveoli (the tissue that moves oxygen through the lungs) until you’re 20, fueling peak respiratory function and flooding your muscles with oxygen during exercise–even at altitude.
D: Energy Muscles and the liver store maximum concentrations of glycogen, a form of sugar that quickly converts into energy during high-intensity exercise and helps you go longer without bonking. Optimize it: To refill energy stores after a long hike, sip 8-10 ounces of fortified hot cocoa (add 1 heaping tablespoon of dried milk to mix), and have a solid meal within 45-60 minutes.
E: Bones Mineral density peaks when you’re 30, making your bones as strong as they will ever be. Optimize it: Carry someone else’s load. Bones achieve peak mass through loading and high- intensity workouts (see Muscles)
F: VO2 Max This measurement of maximum oxygen consumption is a major indicator of athletic potential–and it peaks at 25. When your muscles strip oxygen efficiently, it means more energy and less fatigue. Optimize it: Do intervals. They’ll continue to increase your anaerobic threshold (the hardest exercise you can sustain) and increase your VO2 max.
G: Joints/cartilage/back Total body water per pound of body weight is at its highest between the ages of 18 and 25. All of that fluid helps keep cells elastic, joints springy, and the lumbar discs between vertebrae spongy and shock-absorbing. Optimize it: Cross-train with biking, skiing, and swimming to preserve cartilage health.
H: Muscles Studies show that quadriceps reach their maximum isometric and dynamic strengths when you’re 30. The maximal strength of other muscles peaks between 25 and 35. Optimize it: Build muscle with high-weight, low-rep strength training. Do squats, bench presses, and dead lifts with 80 percent of your repetition maximum (the most weight you can lift once). Do 6 reps, 3-6 sets per exercise.