I was the skinny kid growing up. I started lifting weights in high school to pack on size and ate everything I could lay my hands on. Every bodybuilding magazine I read back then preached heavy training for big muscles and light training for definition, so I went “heavy” every workout. Just to be clear, “heavy” meant choosing a weight that was way too much to lift with good form, then bouncing, grinding, and arching as much as you needed to finish each rep. It was a complete waste of time insofar as building muscle and strength, but the eating part did make a difference. I went from a sinewy 132lbs to a bone-crushing 156lbs in a year.
Then I met a bodybuilder at my high school who had big muscles and lean like I wanted to be but when he trained his reps were done with perfect form and control. He chose a weight that he could control so he could flex and stretch his muscles with each repetition and he would do between 8 and 12 repetitions with each set. I tried that method and for the first time in my weightlifting career, my muscles started to grow.
Weights are used as resistance and when you make your muscles work against resistance, they are damaged then on your days off, if you eat well and rest, your muscles adapt to the workload by getting bigger and stronger. Workouts damage muscle tissue and those muscles repair and adapt to the workload by getting bigger and stronger.
In the 1980’s I began powerlifting competitively. My training had to change completely. My goal was to make my muscles stronger. I needed my connective tissue and nervous system to adapt to moving heavy weight and ultimately a maximum weight for one repetition. Lifting maximum weights also required my mind to adapt as well. Training became less about lifting weights and more about preparing my body for maximum loads, and then recovering after the workouts.
In the early 2000’s, I fell in love with Mixed Martial Arts and the training goals of course were very different. I needed speed, 
endurance, agility, flexibility, but also power and strength. Training changed again and the focus became high-intensity training where I would choose a moderate weight or I would often do drills or exercises that didn’t require weights like battling ropes, tire flips, pushing a sled, or hitting tires with a sledgehammer. Time would be the measurement during this kind of training. I would often train for 30 seconds, then rest for 30 seconds. Sometimes I would train for a minute then off for 30 seconds. It all depended on what I was doing and how long I needed to do it to force my body to adapt by improving. Despite what the magazines said way back in the day, training with light to moderate weight in this manner improved my strength and lean muscle mass as well as all the other things I was training to improve.
The point is, no matter where you are at, your body has adapted to your current workload. If that means you are overweight and you are sedentary, It will take very little work to see changes in your body if you workout consistently and often. Then when that feels easy, you can increase the number of reps or sets you do, you can do the reps faster or slower. You can reduce the rest time, increase the work time, or so whatever you wish to do as long as the work is challenging, and you are changing it up so that your body has to adapt to the new workload. It will adapt by getting bigger, stronger, faster, leaner, and so on.
Your body is an adaptive organism and so if you use muscle, that muscle will respond to the workload, no matter how old or out of shape you are. When you are done working out, eat plenty of healthy foods that will help repair tissue damaged from training and get enough rest so that your body can recover. Train consistently as missing workouts causes your body to adapt to not working out so the progress you made last week is lost if you skip workouts this week.
Most importantly, fitness is a lifestyle. It includes a healthy diet with sufficient carbs, proteins, and fats. It also includes rest and time to recover from workouts. Training too often is counter-productive as your body won’t have time to recover, so you get run down and risk getting injured.
Don’t do something you aren’t excited about doing. I love almost any kind of exercise so I do all kinds of things like running, hiking, swimming, lifting weights, and fighting sports, and in a typical two-week period I do most or all of these things. So have fun with it because if you do, you will be more likely to stick with it.
Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own?For you were bought at a price; therefore glorify God in your body and in your spirit, which are God’s.
1 Corinthians 6:19-20 NKJV
