High volume lower weights or high weights lower volume?

There's always this huge debate in training, which is best..to lower the weight and do lots of reps/sets? or to increase the weight and do less reps/sets? 

Now, the major problem here is.. Muscle fibers. We all have muscles fibers, and we all have different types of muscle fibers in different muscles. Now, these muscles fibers, depending on their type will respond differently to different types of training. It's also worth noting that each individual person will have different amount of each muscle fiber, therefore..people will respond differently to others. 

Fast twitch fibers respond primarily to heavy lifting, they are larger fibers and fatigue quickly. These kind are often more numerous in olympic weightlifters for instance.Slow twitch fibers are used for lighter lifting, they are far more resistant to fatigue and are more numerous in endurance athletes. So, it makes that to stimulate fast you need heavy weights, and to stimulate the slow you'd need lighter weights..but for LOTS of reps (as they are resistant to fatigue) 

If you think about this in context, you can look at say powerlifters for instance, they are fast twitch dominant. Getting 1RM's, stimulating those fast twitch fibers but neglecting the slow twitch fibers. Then if you take bodybuilders, they tend to stimulate BOTH muscle fibers, by using different rep ranges and weights. Bodybuilders for this very reason usually have more muscle.

Someone might say why not just go very light and do LOTS of reps, well, by using that method we're never really stimulating these larger fibers and the rep range would have to be super crazy to even have a profound effect on the slow twitch fibers. So no, lots of body weight squats just won't do. 

So what does this mean for us? Well, it pretty much means that we want to be stimulating both for better results. How do we achieve this? MEDIUM WEIGHTS AND HIGH REPS. Boom. You get the best of both worlds - quote miley cyrus. Pretty much, lift as heavy as you can for a fairly high rep range. You can vary it, mix it up, for different muscle groups. For instance, the quads have a pretty even mix of both muscle fibers and respond well to HEAVY and light(ER) training. I don't mean LIGHT LIGHT, I mean light enough for you to do say 15 reps on leg extensions. 

Now, a lot of people are like..well you have to lift REALLY heavy for you to actually put enough strain on the muscles, you need to be doing low reps etc. Well no, I mean..there is a need for intensity, that is definitely true. However, you can achieve great results without going crazy and hurting yourself. 

There was a study.. ha (here she goes again) whereby men were asked to complete a set of leg extensions with varied reps etc. The first group were told to do 80% of their max weight, for 3 sets until until failure. Another, told to perform 80% of their max for one set to failure. The other group to perform 30% of their max for 3 sets to fatigue.

The results showed a significant increase in muscle gains for all test groups. However, the award for most gains went to.... BOTH THE GROUPS THAT DID 3 SETS. The group that worked a mere 30% of their max did better than the group working at 80% for less reps.

So, pretty much, high reps are good. Don't be afraid of them. 

What I think is important to take from this is....

 everyone is different in terms of what works best for them due to different types of muscle fibers and preferred training methods. But optimally, higher reps for medium weights are a good starter for everyone. You don't NEED to be uncomfortable training at a ridiculous weight, sometimes you can't get the correct form, sometimes even though you're lifting heavier you can't actually FEEL it working because you don't correctly contract the muscle, you don't feel the muscle fibers working, and that's what you want. No matter how you prefer to train, by that last set you should be working to your near maximal effort, you should be really feeling it, to failure or if not almost. That is how you stimulate muscle growth, strain on the muscles so they ADAPT and grow.