How to Design Exercise Programs, Part 4: Intensity and Reps
Muscles grow as the result of Time Under Tension (TUT); this post covers how to identify the right intensity and reps for your goals.
Optimize Your Workouts!
No one likes wasting time yet when it comes to their workouts and a common mistake that often occurs is using the same amount of weight for the same number of reps for too long. Optimize your training time by knowing the amount of intensity and number of reps you should be using for your workouts!
The number of reps for an exercise indicate the number of times to perform that particular movement; i.e. 12 reps = doing that movement 12 times. You’ve no doubt heard the standard gym myth that training for size or strength requires heavy weight for low reps while training to improve muscle definition or ‘toning up’ requires using lighter weights for a number of repetitions.
While there is some degree of truthiness to these claims, know this:
The number of reps you do for each exercise has a significant influence on getting the results you want from your workouts.
7 Things to Know About Reps:
Here are 7 things you should know about the number of reps that you should be doing for your workouts.
A repetition is a single, individual action of the muscles responsible for creating movement at a specific joint or body part. Each repetition involves three specific phases of muscle action: lengthening, a momentary pause and shortening. The lengthening phase is when the muscle fibers experience the greatest Time Under Tension (TUT), for general strength and aesthetic goals the timing should be: 1-3 seconds for the shortening phase, a brief pause and 2-4 seconds during muscle lengthening.
One of the proven, effective methods of stimulating muscle growth is to rep to the moment of fatigue; this ensures that all of the fibers responsible for moving that muscle have been engaged (that’s why you’ll feel your muscles shaking, your CNS is sending electrical impulses to activate more muscle fibers). If your goal is to improve definition and you finish a set capable of performing a few more reps you have not fatigued all of the type II fibers responsible for creating definition. Get the most from your sets: work to that moment where another rep is not possible!
In general, the number of reps you do for an exercise has an inverse relationship with the amount of weight used. As the amount of weight goes up, the number of repetitions able to be performed decreases. Higher-intensity (heavier) loads can only be performed for a few repetitions while light, low-intensity loads can be moved for a relatively high number of repetitions before fatigue sets in. If your goal is to improve aesthetics, would you rather use a heavier weight and achieve fatigue in fewer reps, or use a lighter weight and have to perform an excessive number of reps to reach fatigue? Either way works, you have to determine which you like the best.
Training for definition can be achieved by a couple of different rep ranges which determine how the long a muscle stays under tension. The type II fibers responsible for strength also create the appearance of muscle definition. Definition comes from a muscle maintaining a state of semi-contraction, achieved by keeping a muscle under tension for a longer period of time. Higher numbers of reps performed at a slower movement speed can apply the tension necessary to increase definition. That is why you will generally see 8-to-12 or 12-to-15 reps as the target ranges in many magazines that focus on bodybuilding or figure competitions.
Training for strength, the ability to produce force, requires using heavier loads, limiting the number of reps that can be performed. Heavier weights require more muscle force to move them which automatically recruits more type II muscle fibers; type II fibers rely on anaerobic metabolism which provides only a limited amount of energy and is another reason why heavy weights can only be moved for a few reps at a time, the muscle simply runs out of available energy. If your goal is to improve strength then you should be using weights that cause fatigue by no more than 6 repetitions. If your goal is to improve size, then you should try to reach fatigue between 10-15 reps. NOTE: doing more reps increases TUT, the key to muscle growth!
If you are a runner, cyclist, swimmer or other type of endurance athlete then you are probably more interested in using strength training to support training for your sport. In this case, your strength training program should focus on activating the type I muscle fibers that rely on aerobic metabolism and you should be doing upwards of 20 or 30 reps without reaching fatigue. Endurance athletes need to be as aerobically efficient as possible; strength training exercises using light weights for high reps will help your muscles develop the mitochondrial density and aerobic efficiency necessary to support your training efforts. In this case working until fatigue is not necessary because you’re not trying to add muscle mass; in fact you want to avoid working to fatigue. However, your rest intervals should be kept relatively short, 30-60 seconds, to ensure that your workout creates the necessary stimulus to engage your aerobic metabolism.
Power is the ability to generate a significant amount of muscle force in the shortest amount of time possible. Power training can provide a number of important benefits and it is completely safe IF the appropriate number of reps are used; however, thanks to the popularity of high-intensity workout programs it is often performed in an unsafe manner. Training for muscular power places tremendous metabolic and mechanical demands on muscle tissue and can rapidly fatigue the nervous system responsible for maintaining proper joint mechanics. When doing technical power-based lifts like the barbell snatch, the clean-and-jerk, the push press, box jumps, kettlebell swings or the hang clean the focus should be on the quality of movement and not the quantity of reps performed. For safe, effective power training the rep range should focus on the maximum force output for 1 or 2 reps and, at the most, be limited to no more than 4 or 5. The same is true for medicine ball throws or jumps; the emphasis should be on the quality of movement and not the number of movements performed. Jumps and throws should focus on technique and be performed for no more than 6 or 8 reps at a time; doing more could cause fatigue which significantly increases the risk of injury. Like endurance training, when power training the goal is NOT to go to fatigue, but to complete the assigned number of reps with the best form possible.
Training Goal Repetitions
Endurance ≥ 12
Muscle definition 8-15+*
Maximum strength ≤ 6*
Power
Explosive barbell lifts 1-3
Jumps & medicine ball throws <8
* For best results the last rep should achieve momentary fatigue.
When to Change Programs
Heavy loads apply a mechanical stress to muscle while performing a high number of repetitions creates a significant metabolic stress both of which can stimulate desired physiological reactions like muscle growth or definition. Whether it is by the amount of weight used or performing reps to fatigue the demand on the involved muscles should be sufficient to initiate the neurological or structural adaptations to achieve your desired goals.
As you can see, there is not one, single way to do reps; instead, the number of reps can and should change on a regular basis. The body adapts to an exercise program in about 8-12 weeks, so my recommendation is always to change the amount of intensity and reps when the seasons change. This results in changing your training program throughout the year so you continue placing different stimuli on your muscles.
Here is one model of periodization: when to change intensity & reps
October - December: Strength Endurance
Low-to-moderate intensity for a higher number of reps; this also includes bodyweight workouts which can be a perfect option for the busy holiday season. Doing a quick bodyweight workout of 20-30 reps per movement at home is much better than not doing any workout at all.
January - March: Strength Training
This phase will develop muscular strength and features rep ranges of 6-12 reps to focus on muscle force production
April - June: Hypertrophy Training
In preparation for summer: increase the volume and intensity to improve aesthetics. This phase will feature moderate-intensity for 10-15 reps, working to a point of fatigue.
July - September: Power training
Focus on explosive movement to use muscles differently. The previous 2 phases focused on muscle force production, this phase focuses on the velocity of force production by doing high-speed movements with lighter weights for a limited number of reps (also great for metabolic conditioning).
This is by no means the only way to organize a training program, but it DOES demonstrate how to adjust intensity and reps on a consistent basis so you can constantly challenge your muscles and keep seeing results all year long!