When people hear the word intense, their definition probably differs from most trainers. Intensity can have many meanings, but when I think high intensity, I think shorter duration and maximum effort (a heavy 1 rep dead lift). A 5k jog may seem "intense" to some people, but if you can jog for thirty minutes straight, that's low intensity. However, if you sprint a one-hundred yard football field as fast as you can, the intensity is higher and the duration is shorter. Is one better than the other? Not necessarily....Or is it?
The proper answer to that question is "It Depends". If you're a long distance runner, you need to run long distances. If you're a power lifter, you need to lift really heavy weights. But when it comes to fat-loss, higher intensities with shorter durations are much more effective than lower intensities and longer durations. A good example for better fat-loss would be to go do 10 - 25 Yard hill sprints instead of jogging slowly for an hour on a treadmill. The sprints will take you about 15-20 minutes, the jog will take you an hour. But what the sprints do that the jog won't do is fire more type 2 muscle fibers, release more fat-burning enzymes, trigger the release of more testosterone and growth hormone when you're sleeping, increase your lactate threshold, force your body to repair and recover itself at a more rapid rate, and increasing the EPOC effect. (meaning you will burn more calories and fat for the next day or two). Plus, you don't risk overuse injuries, lower bone density and lower muscle mass. Excessive long distance training (without weight training) will have these adverse effects on your body.
The same can be said in the gym; if you are always doing the same 15 pound overhead presses and the same 30 pound Kettle Bell Goblet Squats for the same exact reps, you will never get better and you will never force the body to adapt and change. You will just create overuse injuries like tendentious. Forget the same old 4 sets of 15 reps, some days try doing more weight (more intensity) and less reps. Instead of 5 sets of 10 squats try doing 10 sets of 5 Squats, but much heavier (assuming your form is money). The intensity goes UP, you get stronger, you get leaner, you decrease the risk of injury and you feel better.
One of biggest pet-peeves of mine is light Kettle Bell Swings, Swings are an explosive and very dynamic movement. Stop swinging a 20 pound KB for 200 Reps. Pick up an 80, 90 or 100 pounder and do 8 Sets of 8 Reps, PERFECTLY. Your heart rate will be jacked and you will force the body to adapt. If you treat yourself like glass, you will be easily broken! Now obviously I'm not telling any "rookies" to go grab heavy weights and kick ass, but after a few months of GC (general conditioning) and your movements are perfect and you're progressing nicely, its time to increase the intensities!
Avoiding this advice will be detrimental to your progress and your health. If you don't mind being weak and having high body-fat, don't change a single thing. But being leaner and stronger will only make you a better runner, a better lifter, a better Mommy or Daddy and better at life.
The bottom line is that everything you do in the gym is goal dependent. If you want better endurance, train slightly lighter weights, higher reps and shorter rests. If you want to be stronger, lift heavier weight, less reps, and longer rests. One is not bad and the other good. It depends. But what is good, is strength! Being stronger is always better than being weaker. You are less prone to injury, less likely to carry excess body fat, and much more likely to be over-all healthier if you're stronger.
Check out the chart above to see what rep range dictates what outcome (assuming you're really pushing hard). If you want to get strong and you bench press 7 reps and stop even though you could have gotten 15 reps, that wont get you strong. If your goal is strength, your reps should be almost to absolute failure. A good rule of thumb is to always leave 1 good rep in the tank. This way you are ensuring your safety...Which is always the most important rule when training!
Don't be afraid to see what your body is capable of - You're a lot stronger than you think! And Ladies, 95% of you will NOT Bulk from lifting heavier, so don't worry about that!
Be Strong, Be Lean, Be a Beast!