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Competitive athletes know that recovery from a match or tough workout is a major determinant of future performance. That's why WHOOP has become a staple among professional athletes, sports enthusiasts and achievers of all stripes. The fitness tracker is designed to monitor physiological markers throughout the day that cause strain, and their impacts on the body's readiness to perform. The lightweight, waterproof strap is worn just below the bone on the wrist, and collects a trove of data, such as heart rate variability, time between each heartbeat, resting heart rate, and sleep quality, to grade your level of recovery. All the information is analyzed and relayed through an accompanying smartphone app and website.—

Since the strap is intended to be worn 24/7-the battery charger actually slides on. the band so it doesn't have to be taken off-it tracks all the stresses in your life, whether. it be a tough three-setter or a tense day at the office. It can recognize when. you're engaged in physical. activity or sleep, and then asks questions to help assess its effect on your body. Strain and Sleep Coach features offer exertion recommendations based on your current state of recovery. It's like having a daily personal trainer that knows exactly when it's time to push it, and. when it's time to hit the reset button.

2. Pocket Radar Smart Coach $400

Want to know if all your serve practice is translating into more miles per hour? The Pocket Radar is a highly portable speed gun—it’s basically the size of a deck of cards—that gives an immedi- ate and accurate reading of a stroke’s velocity. It can be handheld by a coach, attached to a fence, or mounted on a tripod. The device itself has a speed reading, with an integrated smart- phone app that also displays and calls out the number, or relayed through headphones via Bluetooth. Addition- ally, it has the option to take video of each stroke in 8-second clips to match speed to a particular shot. So if you’re tinkering with the grip on your serve or the stance on your forehand, not only will you get instant empirical data on whether the change results in more speed, but you can analyze the footage to combine the new technique with visual cues.

3. Slinger Bag $550

Racquets, string, overgrip, towel, extra shirts—those are just some of the things players typically keep in their bags. The Slinger Bag can handle those assignments and offer a unique extra: a ball launcher. Built into the 33-pound trolley bag is a battery- powered ball machine with customiz- able dials to control the launch speed, angles and frequency of feeds. The bag holds a case of balls, shoots up to 45 MPH with 2-10 second variability, and gets up to five hours of battery life. A remote control provides basic start/ stop functionality for the launcher and oscillator (sold separately). Luggage wheels and extendable handles com- bine for easy transport, and the bag comfortably fits into most car trunks. The Slinger is easy to use, quick to operate, and delivers a feed that can work for a rank novice up to a skilled tournament player.

4. Proton $1595

The Proton is not your father’s ball ma- chine. Weighing less than 20 pounds and with the dimensions of a backpack (15”x17”x9”), it is the ultimate in por- tability. But don’t let its diminutive size fool you—it still holds 100 balls and delivers best-in-class performance and functionality. Produced by a former Apple developer and launched this spring, the Proton employs high- performance drone motors to shoot feeds up to 70 M.P.H. with spins reaching 3,000 R.P.M. Lightweight, quick-change lithium-ion batteries provide its power, with the capability of feeding 1,000 balls on a single charge. The smartphone interface allows users to pick from numerous sophisticated pre-programmed practice routines, or devise one of their own simply by tapping the screen. It’s so complete that you may never need a hitting partner again.