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How to customize your weight training based on your muscle fiber type. 

The more people I introduce to the benefits of proper weight training, and the more I write about it, the more evident it becomes that it seems like one giant black box to most people. 

Few people really get why they need to be lifting weights, they mistakenly believe lifting weights is only for bodybuilders. When you start talking about reps, sets, 1 rep max, percentage of 1 rep max etc, people just draw a blank and think ‘screw that, I’ll just go back to my elliptical trainer’ (yes, I do have a thing against the elliptical.) 

I can’t say I blame them though, some of this crap can be confusing, even as a bodybuilding-obsessed teenager who read everything he could get his hands on – it still took me a while to wrap my head around some of these things.

While one article will never be able to explain all the intricacies of proper strength training (most books don’t even do that adequately), I’d like to teach you how to choose the correct weight and rep-scheme for your program in this article. 

The correct weight and rep-scheme will differ from person to person. It will be depend on your goals, muscle fiber make-up, experience level etc. But, if you want to get optimal results (whatever your goals are), you need to choose the appropriate weights and reps for your weight training.

So many programs are far too generic, they just say something like: 

Bench Press: 75lbs, 3 sets of 12 reps. 

Firstly, what if 75lbs is too heavy for you? 

What if it’s too light for you? 

What if 3 sets is too few for your muscle fiber make-up? 

What if 12 reps is too many for your specific muscle anatomy?

The secret to getting great results is knowing how to ‘tweak’ existing programs, or design your own according to your body and goals. 

When it comes to exercising, it really isn't a one-size-fits-all type of thing.

The problem is, is that there’s a bit of a learning curve in being able to tailor a program to your individual needs. If you have a good personal trainer, you’re luckily able to avoid this learning curve, because they work it all out for you and just tell you what to do. 

However, very few people can afford to keep a trainer on the payroll indefinitely, so what happens when you stop using the services of a trainer? 

How do you ensure that you’re still training in a way that is optimal for you?

If you want the ability to do that, then I’m afraid there is a bit of a learning curve, its unavoidable.However, once you have learnt some of the core, fundamental principles - then you have the ability to help yourself stay in shape for the rest of your life. 

It’s kinda like the old saying, “give a man a fish and he will eat for a day. Teach a man to fish and he will sit on the boat and drink beer all day..”

No wait, that aint it, its “give a man a fish and he will eat for a day. Teach a man to fish and you will feed him for a lifetime..” or something along those lines - you get my point.

It’s my intention with many of my articles to teach you, so that you can stay in shape for a lifetime.Teaching you to choose the correct weight and rep scheme is what I’m trying to do here.

I must warn you though, this article is quite long, and it might get a little dry (I can only spruce up and be sarcastic about Type I and II muscle fibers so much.) I also have to delve into a bit of light science and math here and there, but I do urge you to power through - because if you can follow what I’m saying and implement it, it will make a HUGE difference in your results.

Just to make sure you don’t fall asleep on me though, I’ve put in a funny dog video at the most strategic point to keep you going! 

If you’re still not feeling up to it, no problem, sit this week’s article out and I’ll talk to you next week – but I suggest you still scroll down and watch the dog videos anyway -you’ll at least get a bit of an ab workout from laughing!

- Okay, so here goes -

Whilst all muscles will show SOME response to resistance/weight training, the extent to which they respond will be determined by the individual’s muscle fiber make up. 

As you’ve no-doubt noticed, there are some people who are just good distance runners and others who are good sprinters or excel in power sports. 
Muscle fiber types

One of the reasons some people excel in one athletic pursuit and not another, is largely because of their muscle fiber make up.  As you can see in the picture above, a distance runner and a sprinter have vastly different bodies and that has a lot to do with their muscle fiber make-up and their training.

Types of Muscle Fibers:

There are essentially 3 different types of muscle fibers:

- Slow-Twitch/Type I: These muscle fibers contract slowly and have a high resistance to fatigue. They are typically used in aerobic type activities. They are only able to produce low amount of force (strength)

- Fast-Twitch A/Type II-A: These muscle fibers have a moderate resistance to fatigue. They are typically used in prolonged anaerobic exercise requiring a moderate force output, such as sprinting the 200 or 400 metres.

- Fast-Twitch B/Type II-B: These muscle fibers have a very low resistance to fatigue, but are able to produce high amounts of force. They are typically used in short sprints and explosive type movements such as jumping, throwing etc.

Numerous studies have found that endurance athletes have predominantly type I (slow twitch) muscle fibers, whilst sprinters, high jumpers and power athletes have predominantly type II-A and Type II-B (fast twitch) muscle fibers.

Unfortunately, muscle fiber composition is genetically determined. It can be altered slightly through training, but ultimately we have to play the hand we’re dealt. 

The child of 2 champion marathoners is unlikely to become the next Olympic gold medalist for weight lifting. 

This does not however mean he’ll be unable to build a great body and develop significant muscle mass, it just means he’ll have to train differently to someone born with predominantly fast twitch muscle fibers.

So how do you know what Muscle Fiber type you have?

The only way to determine this with certainty is to perform an invasive muscle biopsy test. These are usually very painful and not really worth the hassle for most people - unless you are a serious, competitive athlete.

There are however some indirect methods you can use that will give you a good idea, that don’t involve having bits of your muscle removed with a needle.

There are a few steps involved:

1. Establish your 1 Repetition Maximum (1RM).

Your 1RM is the greatest amount of weight you can lift ONCE for a given exercise, using maximum effort. 

If you are not a very experienced trainer, this can be a little dangerous, so a better way to do it, is to pick a weight you think you can handle for about 8-10 reps (this will require a bit of experimentation and trial and error.) When you are fully rested, take that weight and perform as many repetitions as you possibly can, using maximum effort. If it is above 10, select a heavier weight, rest and then repeat again (this test doesn’t work too well with reps higher than 10).

After you have found the appropriate weight and determined the maximum number of repetitions you can perform with it, you put those values (the weight and repetitions) into the Epley Formula:

1RM = ((w.r)/30) + w

Where w is the weight used and r is the number of repetitions performed.

The formula works best if the reps are close to 10. The margin of error increases the further you move away from10.

There are other formulas that are perhaps more robust and accurate, but they require a greater degree of mathematical ability, so I will stick to the simplest one. If you would like to make use of other formulas or use a 1 rep max calculator, you can go here.

To provide you with an example, let’s say I could do the bench press with 120lbs for 10 reps.

I’d then put these values into the formula to give:

1RM = ((w.r)/30) + w

1RM = ((120 x 10)/30) + 120

1RM = 160lbs

What that means is that the maximum amount of weight I can use for 1 repetition of the bench press with is 160lbs.

2. Calculate 80% of 1RM

So I know my 1RM of 160 lbs, I calculate 80% of it.

So 160lbs x 0.8 = 128lbs.

3. Perform as many reps as possible using 80% 1RM

After calculating 1RM and 80% of it, make sure you have rested for at least 15 minutes, then perform as many reps as possible using your 80% 1RM weight (in this case 128lbs).

4. Based on results, determine muscle fiber type.

  • If you could perform 12 reps or more then you have more than predominantly slow twitch muscle fibers.

  • If you performed between 7 and 12 reps then you have an equal proportion of slow and fast twitch fibers.

  • If you performed fewer than 7 reps then you have predominantly fast twitch muscle fibers.

Note: Perform this test using a compound movement such as bench press, Pull-ups or dips for the upper body. The legs typically have a higher proportion of slow twitch fibers than the rest of the body, and should generally be trained with slightly higher reps anyway.

Right, so you've made it this far. You hopefully know how to determine your muscle fiber type. Before we get to the next part, where I will teach you how to put that into practice and customize your training, here is a funny dog video as promised, just to make sure you don't zone out and lose concentration on me..

Okay, so hopefully you're still following and with me after that. Right, so you know your muscle fiber make up:

What does this mean for your training?

Your fiber type proportion will play a big role in the amount of weight you can lift, the number of reps you can perform, how quickly you recover etc.

As a GENERAL RULE it has always been stated that you should use the following rep ranges depending on your goals:

  • If your goal is Strength and Power: You should perform exercises in the 2-4 repetition range.

  • If your goal is muscle hypertrophy (growth): You should perform exercises in the 8-12 range.

  • If your goal is anaerobic strength endurance: you should perform exercises in the 12-20 rep range.

  • If your goal is aerobic strength endurance: you should perform exercises in the 30+ range.

While these rep ranges will GENERALLY still hold true, you need to take some things into consideration now that you know your muscle fiber make up:

If your muscle fiber make up is predominantly slow twitch:

If you are looking to increase muscle mass you need to use higher reps. If the usual rep range for hypertrophy is 8-12, you should be at the high end of that spectrum, performing 12 reps per set usually, but don’t be afraid to throw some 15 and 20 rep sets in there from time to time.

Occasionally you still need to schedule some low-rep (3-6) rep training to hit the fast twitch fibers you do have, but the majority of your training should be directed more towards slightly higher repetition training.

If you have an even mix of slow twitch and fast twitch muscle fibers:

The standard guidelines (above) will work best for you. Just make sure not to get stuck using only one rep range because then you’ll only be training half the muscle fibers you have. You need and even mix of higher, medium and low rep training.

If your muscle fiber is predominantly fast twitch:

If you’re looking to increase muscle mass, you need to stick to the lower end of the spectrum for the hypertrophy guidelines mentioned above. Your hypertrophy training will probably be optimized in the 6-8 rep range.

You’ll also want to include frequent low (2-3) rep sessions to target those type II-B muscle fibers.

You’ll occasionally want to do some higher rep work as well, to stimulate the slow twitch fibers you do have, but the majority of your training should be for lower reps.

How many sets should you do?

Slow twitch fibers recover more quickly than fast twitch fibers, so people with predominantly slow twitch fibers can handle more sets, but they cannot handle much weight. If you’re predominantly slow twitch then 5+ sets per exercise for higher reps will probably work well for you.

People with an even mix of slow twitch and fast twitch fibers will do well with standard set prescriptions of 3-4.

People with predominantly fast twitch fibers should not perform more than 3 sets, especially when using very heavy weights for low reps.

These methods are not infallible and do have some degree of error, but for the average population they are pretty accurate. 

How do you choose your weight?

So far you have calculated your 1RM and optimal rep and set ranges. The last thing in the recipe is choosing the appropriate weight for those rep and set ranges.

This is not too difficult to do. You have already calculated your 1RM and you know the number of reps and sets you’re trying to perform, so just read the corresponding number of reps and percentage of 1RM from the table below: 

Using the previous example of the individual with a 1RM of 160lbs – let’s say he was able to perform 8 repetitions with 80% 1RM (128lbs). This tells us he has an even mix of slow and fast twitch muscle fibers.

If he is looking to increase muscle hypertrophy then he should choose a rep range of 8-12 repetitions (as mentioned in the general guidelines). 

Lets say he decides on 10 reps per set.

Based on the table he’d then select a weight of 75% of his 1RM to be able to perform 10 reps. This works out to 120lbs.

It’s not an exact science, but it’s a good starting point for anyone, and with a little trial and error, you’ll quickly find out the optimal weight to use.

When do you increase weight?

You should increase weight when you’re able to perform 2 repetitions or more above your specified rep range in your final set, in 2 consecutive workouts.

If you’re a beginner, your progress will be rapid, so you can increase it by 5-10%. If you’re an advanced trainee, try increasing it by 2-5%.

How long should you rest between sets?

  • If muscle hypertrophy is your goal, then you should rest for 30-60 seconds between sets if you have predominantly slow twitch muscle fibers. 

  • If you are an even mix of fast and slow twitch fibers, then 60 seconds between sets is a good rule of thumb. 

  • If you’re predominantly fast twitch, you need a bit more rest, so 90-120 seconds is a good guideline.

  • If you’re training very heavy and for lower reps (4 and below) then longer rest periods of 2-4 minutes might be necessary depending on what weights you’re moving.

And there you have it - how to choose the correct weight, reps, sets and rest intervals for your unique body type.

I know it was a lot to take in and remember, but give it a try. Customizing you training to suit your body like this will bring you far superior results to just using a generic program.

But remember, don’t get stuck using only one rep and set range - whilst some should be dominant over others, don’t forget to mix it up, you have to keep your body guessing!

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