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Screen print: Kate Gibb; Photograph: Michael Elins
The Algorithmic Workout
Marc Digesti logs on to one of the weight-free CPro resistance stations at the Core Performance Center in Santa Monica, California, and downloads a custom workout designed by his new coach: an algorithm. After tapping through a body-part map that allows him to note injuries, Digesti begins pulling a cord as directed by an onscreen video. As he guns through five reps of a biceps curl, the monitor displays his power output in watts for each arm. "You can see that I fall off a bit on these last reps," Digesti says breathlessly, while the screen message "Behind schedule!" prods him onward. "Next time the system might give me a little less weight."
At Core Performance, personalized workouts have been digitized and automated — think Club One run by Deep Blue. The gym's founders spent two years poring over decisions made by a coach and embedding them into workout equipment that compares a gym rat's goals (say, run a marathon) with their stats (like VO 2 max) and nutrition habits to calculate a progressive series of workouts. Data from each session is saved in order to improve subsequent ones. The principle is that workouts you measure are workouts that make you fitter — because you train more precisely and work harder when you're getting quantitative feedback.
Core Performance charges up to $65 a workout — what many gyms charge for a month. 
But the idea is spreading. At Wicker Park Fitness, a Chicago gym that costs $500 a year, customers can plug their USB drives into cardio machines and store info like time, distance, incline, and calories. And YMCAs around the country also now let customers use a similar system.
Wicker Park co-owner Mason Goldberg is convinced that obsessing over the numbers helps: "People love to track things. It brings out their competitive spirit." — Jennifer Kahn
5 Exercise Tools
Garmin Forerunner 310XT Garmin's latest GPS watch uses wireless ANT+ and networking to send data straight to your desktop. Plus, it's waterproof, so you can splish-splash without a crash. $350, garmin.com
Training Peaks 3.0 Training Peaks sucks up data from dozens of fitness devices and reports back with visualizations of heart rate, power output, speed, distance, elevation, and much more. $119/year, trainingpeaks.com
RunKeeper Pro Turn your iPhone into a mobile fitness center. Using the GPS chip in 3G iPhones, this app tracks speed and distance and lets you upload and share your routes on the company's site. $10, runkeeper.com
WeEndure Performance monitoring meets Web 2.0 trash talk. This social network not only logs your data, it also shows your friends' numbers so you can "comment" on their workouts. $20/year, weendure.com
SMHeart Link This little gadget syncs with your favorite exercise gear — heart rate monitors, power meters, even fitness equipment — and sends the data back to your iPhone or iPod Touch wirelessly. $125, smheartlink.com
GPs + Idaho = Gold Medal
In late 2007, when cyclist Kristin Armstrong first rode the course she would compete on in last year's Summer Games, it was so steep that she suspected her coach was punking her. It was no joke; the punishing route rose some 1,200 feet over the first 6.7 miles. But the 2006 world time-trial champion had a secret weapon: GPS. Armstrong exported the GPS tracks of the course from a Garmin Forerunner 305 and began looking for a similar training climb. She found a nearly perfect match right in her Boise backyard — the incline up Bogus Basin, a ski area 15 miles away — and started muscling her way up it every week. She also watched Google Earth flyovers of the Olympic course, memorizing its nooks and crannies. Those tech-enhanced preparations paid off: Armstrong struck gold in Beijing, winning by just over 24 seconds. "We're all great athletes and know how to train," she says. "It's everything else you do that's going to make you win that day." — Mathew Honan
| Bogus Basin Course GPS Coordinates
Testing Your Limits
What's the single most important metric for athletic performance? Lactate threshold. During intense exercise, your body relies on carbohydrates for fuel. Carbs break down into lactic acid in your muscles, which becomes lactate in the blood. Your lactate threshold is the point at which your body produces more lactate than it can remove, causing fatigue; it's the biggest hurdle for endurance athletes. Training just below this threshold and crossing it for brief intervals improves your body's ability to process lactate, raising your lactate threshold heart rate (LTHR). The result is that you can work harder and longer, leading to faster race times. Here's a simple test to determine your LTHR: After warming up, strap on a heart rate monitor and run for 30 minutes as fast as you can. Ten minutes into your run, hit the monitor's lap button. Your average heart rate in the final 20 minutes is your lactate threshold heart rate. — Mathew Honan
Power Meters Track an Athlete's True Mettle
During the National Hockey League's 2004 season-long lockout, veteran player Curtis Leschyshyn took the chance to completely change his workout routine. An avid cyclist, Leschyshyn looked for a new way to get in shape.
"Hockey training is a lot of short sprint efforts and weight work, simulating what we do on the ice," Leschyshyn says. But for an endurance sport like cycling, he had to meet different goals. His conditioning coach, Neal Henderson at the Boulder Center for Sports Medicine, helped set him up with a power meter, which directly measures the raw output a rider produces.
"When I'm riding, even if I think I'm going good, if the watts are off I know I'm not where I need to be," Leschyshyn says. "Power is a true indication of what's in the tank. It's not that I don't watch heart rate anymore, but I'm much more inclined to make sure I'm producing the watts. Heart rate isn't a true indication of your effort."
Right now, power training is limited to cycling, where the human-machine interface allows direct measurement. But improving GPS technology and algorithms offers the possibility that, someday, power training might transfer to other sports. Even hockey.
"If I could've worked with a power meter a few more years, I think I could have found a way of training to increase my power and quickness on the ice," Leschyshyn says. –Joe Lindsey
DATA POINT Heart Rate
Sure, your ticker speeds up when you're working out. But the benefit is that it works less the rest of the time. Conditioned athletes have much lower resting heart rates.
» Elite athlete Maximum heart rate…200 bpm Resting heart rate…32 bpm
» Average 30-year-old Maximum heart rate…190 bpm Resting heart rate…70 bpm
Living by Numbers
The Nike+ Experiment: How the Shoe Giant Unleashed the Power of Personal Metrics
How to Live by the Numbers: Nutrition
How to Live by the Numbers: Health
Know Thyself: Tracking Every Facet of Life, From Sleep to Mood to Pain, 24/7/365. Brainy Trainer: Workout Monitor Tells You When to Chill
