As with any fitness activity, it’s important to exercise with proper technique, however. The big muscles in the legs are where most of the workout action should be. Injury to the lower back can occur from bending too far forward in the row. It’s best to maintain a upright 90 degree angle to the rowing machine’s seat and slider bar. Using the legs for the motion rather than relying as heavily on the back or arms can help reduce the chance of muscle pulls or other related injuries. Always check with a physician before starting any new fitness regimen.
We picked the brains of rowing coaches, fitness experts, and physical therapists to learn what features make for an exceptional rower. Based on their input, we searched the market for air and water resistance rowing machines, then tested the best for ride feel and design. We found one model of each type — air resistance and water resistance — that felt truly superior to the others.
The Classic Rowing Machine is generally quiet for a water resistance machine, but some users believed that it was a little noisy. Like all rowers, whether it’s a flywheel or a waterwheel, there is going to be noise. The more effort that you put into it, the louder it’s going to get. And most find it motivating to hear the water paddles get louder as they burn more calories.
Although some rowing machines are made of space-age, super-sweat-resistant metals, you still want to wipe off the equipment after a sweaty workout.  These machines are usually constructed with a lot of various materials and salty sweat can be very corrosive.  Keeping your rowing machine clean can go a long way toward extending its life, and its appearance.
The Challenge AR has the capability to allow the rower to control and adjust the resistance from “Feather light” to “Olympic sprint” delivering a silky smooth resistance to the user’s effort and instantaneous response to input with no “flat sport”.  With water resistance being the most accurate manner in which to simulate actual outdoor rowing, the Challenge AR provides a smooth and consistent sensation throughout the range of motion of the exercise experience.  
Another negative point for me is the angle of the seat. Unlike the Concept2, it has a slight backward angle, which makes it easier to maintain good form at the end of the stroke. Given that the Waterrower has greater resistance at the catch, it puts more pressure on the lower back at this point making it uncomfortable for people like myself with lumbar spine problems.
According to Men’s Total Fitness, rowing machines are not only great for aerobic workouts, but they also work all of your body's major muscle groups. What’s more, you don’t have to go to the gym to work out on a rowing machine, as many manufacturers make high-quality rowing machines -- and even rowing machines that fold up for easy storage -- that are suitable for home use. Two popular types of rowing machines are the water rower and the air rower.
The WaterRower Natural is outfitted with a Series 4 performance monitor that's designed to balance technical sophistication with user-friendliness. The monitor--which includes six information and programming windows, six QuickSelection buttons, and three navigation buttons--displays your workout intensity, stroke rate, heart rate, zone bar, duration, and distance. Plus, the monitor is compatible with an optional heart rate chest strap and receiver, which helps you optimize your workout and achieve your exercise objectives.
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