Fit hikers in this age range routinely overtake huffing and puffing twentysomethings on big days. That’s because endurance performance reaches its absolute peak in the late 30s. Long-distance runners and most mountaineers achieve their greatest physical potential during this range–but not because of some physiologic overdrive. In fact, muscle strength and VO2max are both on the decline. It’s because muscles are working together with maximum efficiency, says Steve Reichman, assistant professor at Texas A&M’s Department of Health and Kinesiology.
A: Heart Maximum heart rate drops as a result of stiffening tissue, hampering your ability to crush steep inclines. The Fix: Increase stroke volume (the amount of blood pumped through your body with each heart contraction) and efficiency with endurance training. The American College of Sports Medicine recommends upping your exercise to at least 150 minutes per week at 65 to 85 percent of your target heart rate.
B: Muscles Fast-twitch muscle fiber–the type used in sprinting and power moves–decreases between 4 and 10 percent per decade beginning at age 40 in sedentary adults. But slow-twitch muscle–the type used in endurance training–remains strong. The fix: Build power for butt-busting ascents with hill workouts, advises Lynn Millar. Fast climbs up short, steep hills (anaerobic), followed by slow descents (aerobic) force those fast-twitch muscles to work on the way up, while measured descents will hit slow-twitch muscles. Try them in sets of five.
C: VO2Max The maximum amount of oxygen the body uses during strenuous exercise trends downward at a rate of 5 to 15 percent per decade after age 25, says Trent Hargens, Ph.D. The fix: Studies show regular cardiovascular exercise can limit the decline in your VO2 max. Achieve this by building muscle and stressing your cardiovascular system with aerobic exercise (see Muscles).
D: Joints/cartilage/back Height decreases about 1 centimeter per decade after age 40, a result of decreased body water and the compression of the gel-like fluid between vertebrae. The Fix: Kelly recommends reducing accumulated stress with inversion therapy–hanging upside down on a pull-up bar for 15-20 minutes, 3-5 times per week.
E: Bones Bone density reaches stasis as osteoclasts (which trigger bone resorption into the body) catch up to osteoblasts (which create bone). This puts bone density in a holding pattern, but poor nutrition can lead to osteopenia, a precursor to osteoporosis. The fix: Take 1,000 milligrams of calcium per day, drink plenty of D-fortified milk, and eat salmon, tuna, and mackerel, all packed with vitamin D.