Strength Training VS. Cardio
Strength is the place to put your time, money, and energy, even if cardio is fun and readily accessible. There is a large misunderstanding on how the human body adapts to physical activity. The questions "should I do cardio for weight loss?", "if I do strength training, don't I have to do cardio too?", "won't having bigger muscles hurt my cardio?" come up a lot. The overarching answer to these questions is that strength training will improve your cardio substantially, but cardio will not help your strength much.
Strength training IS cardio
Strength is the ability to produce force against an external resistance. Many adaptations occur in the process of getting strong. Of course your muscles get bigger, but your bones also get denser and stronger, your tendons get stronger, even your arteries get stronger and thicker. Your cardiovascular health also improves. Strength training might not seem like it would improve cardio, but three heavy sets of five reps will massively raise your heart rate and make you out of breath.
Conversely, running, swimming, bicycling, and walking will improve your ability to metabolize fat and sugar into useful energy, but they will not make you appreciably stronger unless you start off extremely weak. This is because a muscle that isn't stressed with sufficient weight will not get stronger, because it doesn't need to. But a set of five squats will absolutely require your body to deliver oxygen and pump blood effectively - thereby improving your cardio.
Cardio is also fast adapting - you can get good cardio in a short period of time. You will also lose that cardio extremely quickly if neglected, but strength does not change quickly. Getting strong takes time, but once acquired, it also takes a long time to lose. A runner might lose 90% of their progress by taking a month or two off. A lifter, however, might only lose 5% of their strength in a month or two month layoff. This is because strength adaptations are primarily structural. Cardio adaptations are chemical which are gained and lost more quickly.
Weight loss
Finally, many people do cardio to lose weight, but this is misplaced effort. Exercise is good, but doesn't matter much if caloric intake isn't reduced. Building muscle will firm up arms and legs and make it easier to burn fat, but the kitchen is really where weight loss happens.
There are many attributes of training, but strength is one that affects all others in a way that the others cannot affect strength. [https://blackmetalstrengthtraining.com/education/2017/3/5/improving-overall-fitness-strength-gets-it-done] Everyone has limited time and energy. Strength training will improve your cardio and many other aspects of your physical being. Strength training only requires three hours a week and can change your life if you commit to it.
