Conditioning for general health purposes generally involves improving your VO2 max, since it directly correlates with cardiovascular morbidity and mortality. VO2 max is a measurement of your body’s capacity to use oxygen, which depends on how efficiently your heart pumps, how well your lungs work, how much hemoglobin you have, the amount of muscle you carry, mitochondrial density, and a bunch of other cellular adaptations that occur in response to increased cardiorespiratory demand.
While strength training and steady-state cardio (aka endurance) create some improvements in VO2 max, the best way to improve it is to train it directly. This is best accomplished through high-intensity efforts using as many muscles at the same time as possible.
That’s where the prowler, or sled, comes in. It is hands-down the most time-efficient way to get your heart rate and respiratory rate (and hence VO2) as high as possible as fast as possible, using as many muscles as possible. It gets the job done in the least amount of time, and is easily progressed depending on your level of strength and conditioning, since you can just add weight. Because it does not involve an eccentric component like the high-impact exercises generally included in HIIT style training, it is much less likely to make you sore and induce muscle damage, and is consequently less likely to interfere with strength training. This makes it an ideal conditioning modality.