The answer to that question depends on the end goal. A lot of people feel strength training should be done first to augment the amount of fat burnt during cardio, because the strength training will burn glycogen stores. But, because of the rest periods and the shorter bursts of exercise, this will not likely affect your glycogen levels. However working in such a state can have negative effects such as low blood insulin, and a strong perception of fatigue. Currently there is no research showing that strength training before cardio increases fat burn. Strength training first may reduce your intensity causing your cardio training to suffer.
If the goal is strength, then resistance training would be the best way to start. If weight loss or aerobic endurance are the goal then hit the cardio first. Alternating the 2 is a great way to train both.
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