I feel machines serve a better purpose attracting members to gyms, but do little for their training. Statistically, more people are injured each year exercising on machines than with free weights. Machines often limit or force a one size fits all range of motion on the user. They also tend to isolate muscles or joint actions that perform better with mutlimuscle multijoint movements. A functional approach to training would involve working the body as one, while mimicking real life, or athletic movement; training movements, not muscles. The exerciser would be better off learning the squat pattern, for example, a fundamental movement, than isolating the various parts of that pattern via a hip abduction/adduction or a knee flexion/extension machine. As the gym culture mentality shifts, you ll be begin to see less gyms full of expensive cardio and resistance machines, and more open space full of free weight and other functional resistance equipment. Next time you re in the gym, take a look at what members are doing with their trainers. Take a look to your left and right, if a trained fitness professional does not have a client on the elliptical next to you, maybe you should be over by the kettllebell rack doing cardio too!! :) Take a look at this article on the oxygen cost of kettlebell swings. Theres alot of science - exercise physiology behind it, but to suffice to say, kettlebells provide a useful conditioning tool for fitness professionals. Performing a two handed kettlebell swings can improve the cardiorespiratory fitness of athletes and amateurs. However, fitness professionals should be aware that HRs achieved during continuous kettlebell exercise are significantly higher than the corresponding exercise V_ O2 demand. This explains, why your heart spikes during compound resistance training movments, but does not always have an aerobic benefit. Furthermore, the relationship between the 2 variables is greater than that noted for circuit weight training but less than that for treadmill exercise. Check out fellow New York City personal trainer, Tom Weaver, performing a Kettlebell swing.