Why You Should Lift (Relatively) Heavy - And the Science Behind It
We’re all aging. For some of us, the aging process might feel faster than for others but the fact is, none of us are getting any younger. When it comes to muscle mass, research suggests that after 40 years of age we lose about 5% of muscle mass per decade with even more accelerated losses after the age of 65 (Candow et al 2011). Obviously we all want to maintain and/or gain muscle as we age but there’s something more important at stake here - the loss of strength and power!
The biggest culprit to losses in power, strength and muscle size are…. LIFESTYLE factors!
The biggest culprit to losses in power, strength and muscle size are…. LIFESTYLE factors (Hakkinen et al 1998). When we’re in college/university, there’s added motivation to lift weights (like wanting to make the football team or impressing the gal down the hall) but once we begin the 'real world', it feels increasingly difficult to hit the gym. The fact of the matter is, the decline in muscle and strength can not only be attenuated, it can be regained, and it doesn’t take very long.
One particular study, (Candow et al 2011) out of the University of Regina, compared the body composition and strength levels of a group of physically active men (between the ages of 20-30) to older inactive men (over the age of 60). Both groups underwent some initial testing while ONLY the older men performed a 22 week weight training intervention. After 12 weeks, many of the older men were on par with the younger men when it came to lower-body strength and after 22 weeks, there were absolutely no differences between the 2 groups when it came to strength and body composition.
In about 5 months, these older men added, on average, 70 lbs to their bench press - isn’t that enough motivation to start training today?
There’s one caveat, they lifted heavy, relatively speaking. In this case, heavy refers to about 70%-80% of their 1RM with reps ranging from 5-10 per set. Obviously they had tremendous results but I’ll argue that greater increases can be expected by lifting even heavier.
The science behind lifting heavy
Lifting heavy works because of the Size Principle. Let me quickly go through some basic physiology of the neuromuscular system (the system that controls movement, allows us to develop force and perform every action possible). When we want to move, a signal is sent from our central nervous system (either our brains or spinal cord - depending on the task). It begins in the cell body, runs down the axon (akin to an electrical wire) until there’s an impulse at the level of the muscle fiber - this is called the neuromuscular junction; the area where the dendrites (branches of the axon) meet the muscle fibers (Figure 1 below).
Figure 1 - Motor Unit
A motor neuron (Figure 1) AND the muscle fibers that it innervates (or excites, for lack of a better term) is called the motor unit. There are 3 types of motor units - this is where things become interesting.
Motor Unit 1 - Slow Motor Units
These are primarily associated with type I muscle fibers, the ones that have tremendous aerobic capacities and are very difficult to fatigue
Motor Unit 2 - Fast Fatigue Resistant Motor Units
They have larger axons and can therefore send a greater electrical impulse at a much faster speed. These motor units innervate type IIA fibers which can develop more force than type I fibers but fatigue at a faster rate.
Motor Unit 3 - Fast Fatigable Motor Units
They have very large axons, send rapid impulses to type IIx fibers which can generate high levels of force, or near-maximal, AND in very short time periods.
When we need to exert force - to lift a coffee mug, run 5k or tackle a running back - we recruit different motor units and their associated muscle fibers.
The recruitment pattern is based, however, on the amount of force that needs to be developed. So if you’re lifting a coffee mug, which requires very little force, you’ll recruit only the slow motor units (the ones that can last a long time). On the other end of the spectrum, if you have to tackle a running back or perform a near maximal deadlift, your nervous system will be on full demand and you’ll need to activate your type IIx muscle fibers (the ones associated with fast fatigable motor units that can generate lots of force). There is one caveat - the Size Principle has a rule which states that no matter what the movement, the neuromuscular system ALWAYS begins by recruiting slow motor units first, then fast-fatigue resistant and finally, if necessary, fast fatigable motor units. Figure 2 helps visualize this Size Principle.
This is why lifting heavier loads is so effective in promoting both strength and size, you effectively recruit both your type I and type II muscle fibers, thus, providing the biggest bang for your buck when it comes to training.
Figure 2 - The Size Principle
Practically, Why Lift Heavy?
Recruit all 3 types of motor units because of the Size Principle - Overall, this equates to a higher muscle activation. For example, if you’ve ever performed a heavy squat, you know that it’s more than just the legs that are firing, your grip is tighter, your shoulders are locked, your trunk is as hard as an iron. THIS TYPE OF LIFTING GETS YOU STRONG.
Type II fibers have a greater potential for hypertrophy (i.e. muscle growth) - For muscles to grow, there needs to be a large enough stimulus. Lifting heavy provides this type of stimulus, especially for type II fibers.
You don’t have to lift to failure to reap unbelievable benefits - With heavier strength training, you don’t have to train to muscular failure for increase is size to occur
As we age, we see a greater loss in type II fibers than type I (Hakkinen et al 1998) - And you won’t get more of them by running.
To move heavy loads you have to have intent to move the load quickly - Even if that load is moved at a slower pace, this ‘intent’, is critical for the recruitment of high-threshold motor units - the ones that innervate type II fibers.
Now, just because I’m writing about lifting heavy doesn’t mean you should go out and squat 400lbs tomorrow. For those of you new to lifting weights, if holding a small dumbbell during a squat feels heavy, that’s ok. Beginners have a large window of adaptation that will allow them to increase load at a pretty fast pace. Intermediate and advanced lifters, adding some additional load may be what your training is lacking. Here are few recommendations that will help anyone with the heavier strength training needs.
Basic Strength Training Recommendations
Use compound lifts - This classifies as exercises like squats, deadlifts, lunges, presses (overhead press, bench press etc.) and pulls (bent-over rows, pull-ups etc.) because they use many large muscles groups across multiple joints.
Keep reps on the lower end - Perform maximum of 8, although 3-6 is best as it really pushes your nervous system (note**, if you can perform more than 6 comfortably then the load isn’t heavy enough).
Don’t stop at 3 sets - You probably don’t hear this too often but it’s ok to do more than 3 sets of an exercise. In fact, the more experienced you become and the heavier the loads become, the more sets you can perform. Olympic weightlifters often times perform more than 10 sets on their big lifts. This doesn’t mean that you have to do 10 sets but you can surely do more than 3. A study found that a 5 set protocol was better than a 3 set protocol at increasing both muscle size and strength (Kelly et al 2007).
Increase your rest times - Get good recovery by going up to or more than 3 minutes between sets. That said, this is just a general rule of thumb. I often times go by how ‘recovered’ I feel - meaning, if I can do another set with the same load before the 3min rest mark, then I’ll do it.
Perform supersets when crunched for time - It’s ok to perform another exercise right after the first one (termed a superset). Ideally, you choose an exercise that has a different muscular demand as this will still allow the you to recover from the previous exercise. Example, perform a back squat first followed by a lat pull-down.
Although training to failure, doing circuits and jumping all over the gym may feel more fatiguing, it won’t help with your strength & muscle goals and it surely won’t prevent injuries (in fact you may be more at risk performing elaborate circuits).