It’s no secret that cardiorespiratory training has enormous health benefits and is a great way to shed fat. If you are a new exerciser, it 
is very important to know your cardio limits to give your body a chance to adapt to the new exercise protocol your body is embarking upon. If you try to do too much too soon, you could do more harm than good. It’s good to push yourself, but your heart has to be ready. The heart is a muscle just like any other. You wouldn’t grab 50 pound dumbbells and start curling to your max after doing little to no lifting for a previous period of time. Likewise, you shouldn’t go out and try to run for an hour if you have been living a relatively sedentary life for the better part of a decade. Conversely, if you are a habitual exerciser, knowing your cardio limits may actually help you realize you haven’t been doing enough cardio.
Knowing your cardio limits starts with defining your current activity and exercise level. Every exerciser doesn’t fit into the exact same framework for recommended cardio amounts. It all depends on your exercise history and current physical activity level. If you are a new exerciser, or an experienced past athlete who’s been off his or her game for a while, you will have to establish an aerobic base for your cardio training. This is huge for new exercisers, because you need a positive experience to help you establish the habit of regular exercise. Too often, people will decide to change their lives through fitness and order an intense fitness program from TV which presents too much of a challenge – and pushes them past their cardio limits initially! The excuse then becomes, “This is too hard!”, and by “this” they mean “exercise”. This is a terrible formula for sticking to a workout plan.
The American Council on Exercise (ACE) has established a four-phase method for cardio training. Be honest with yourself and see where you fit in to know your cardio limits.
Phase 1 – Aerobic Base Training. For new exercisers or those out of shape living a sedentary lifestyle. You would also train in this phase if you do some moderate exercise sporadically and are mildly or moderately deconditioned. Your fitness classification would be labeled poor, fair, or average. Your weekly duration of cardio work (in minutes) is 60-150 if you are in poor shape, 150-200 if you are poor to fair, and 200-300 if you are fair-average. Your cardio should be in steady-state form, meaning your heart rate is not getting too high, and the workouts are moderate to somewhat hard.
Phase 2 – Aerobic Efficiency Training. Progress to this phase once you can maintain exercise for 20-30 minutes at a moderate to somewhat hard intensity level. You will begin to increase your heart rate in this phase, and you can introduce new variety to your programs. Most people workout in this phase for years. Your weekly max duration will be in the 200-300 minute range (30-90 minutes per day) with the option for slightly more vigorous interval training.
Phase 3 – Anaerobic Endurance Training. Train in this phase if you have some specific endurance or performance goals – perhaps a half or full marathon? Even a 5k run would call for training in this phase. Your cardio will be in longer bouts, still maintaining the feeling of working at a “strong” level, but not to exceed a feeling of “very very strong”. At that point, you would be approaching your maximal exertion level. This phase is reserved for exercisers who engage in regular habitual physical activity. Your weekly max duration will be in the 200-300 minute range (30-90 minutes per day) and most of the cardio work will be more vigorous than Phase 2.
Phase 4 – Anerobic Power Training. Know your cardio limits! This phase is saved for those who need to build up their bodies to sustain short bursts of exercise at almost-maximal effort during competitions or events. These training cycles will occur close to competition times and are mostly high-intensity power intervals. Always check your heart rate and stay in a safe zone. This phase is for exercisers who do high amounts of regular, habitual vigourous-intensity activity.
