6 Key Training Variables Important for Strength Development

It is important to manage specific training variables in order to build muscle, connective tissue, and increase strength. The following six training variables need to be manipulated over the course of a strength & conditioning program to avoid overtraining and ensure optimal gains.

Training Variables

The six key variables discussed here are: (1) intensity, (2) repetitions, (3) sets (4) time under tension (5) rest period and (6) exercise selection. While these variables are discussed separately, they are all interconnected and play off each other. In addition, other variables to consider, but are not discussed in depth, are training frequency and training volume.


In order to increase strength, and build muscle, training intensity needs to be at the top of your mind. Many are consistent with training programs but a great deal, especially novices, miss the boat with this key variable. Everything else can be spot on but if adequate intensity is a no show, gains will be sub-optimal. The intensity must be high enough to generate stress, but low enough to allow sufficient repetitions for fatigue. Research has suggested that a moderate intensity (75-85 percent of 1-repetition maximum) is sufficient.

There is a reason why Jefit app offers the ability to track 1-RM testing (one-repetition maximum). Once strength is assessed, the goal is to use a specific 1-RM percentage during a workout. As with anything, you want to progress slowly, but ultimately you want to be working at about 80-percent (and greater) of a 1-RM to increase strength.


There is a repetition continuum from approximately 1-15+ that you can consider depending on training goals. This example was used by Shoenfeld and colleagues in a previous research paper. Working from the left of the continuum builds strength while moving further right, develops muscular endurance. Conversely, The American College of Sports Medicine recommends 12-15 repetitions of a light load to increase endurance, 8-10 repetitions of a moderate load for hypertrophy, and 3-5 repetitions of a heavy load to build strength. 

Repetition Continuum


A given number of repetitions make up a set. A set describes a group of repetitions performed for a particular exercise. When looking to build additional muscle mass, use the following “general guidelines” from the National Strength & Conditioning Association (seen below). Additional research as well as the National Academy of Sports Medicine offer similar guidelines.

  • 2-3 sets will help build muscle endurance
  • 3-6 build muscle hypertrophy
  • 3-5 build muscular power
  • 2-6 build muscle strength

Time Under Tension

Time under tension (TUT) is the overall time a muscle is kept under stress. For example, a bicep curl, using a 1/1/3 format for 8 repetitions, equals 40-seconds of TUT. You may have only a few seconds of TUT when performing maximal repetitions on a heavy bench press. The average gym-goer, though, should aim to be in that 35-45-second area for each repetition when starting out.

Rest Period

Less recovery time between sets will help improve muscle endurance. The heavier you go on a set, the more rest time you’ll need between sets. Keep in mind after approximately a minute of your recovery your muscle “energy” stores are about only 80-percent recovered.

Exercise Selection

Exercise selection is important to meet the needs of an individual training plan. Different exercises place different amount of stress on a muscle. It is important to use exercises that work muscles through a full range of motion and (hopefully) multiple planes of motion.

When the goal is both strength and muscular development, multi-joint exercises are highly recommended by coaches at all levels. These are foundational movements such as a squat, deadlift, bench press, shoulder push press, carries and rows.

As you plan and track your workouts this year using Jefit app, pay close attention to each of these training variables to take your exercise program to the next level.


Shoenfeld, et al., Sports (Basel). 2021 Feb; 9(2): 32. Published online 2021 Feb 22. doi: 10.3390/sports9020032

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Millions of members (9.7 million to be exact) are having great success using the app. Jefit is a fitness app that comes equipped with a customizable workout planner, training log, the ability to track data and share workouts with friends. Take advantage of Jefit’s 1400 exercise database for all of your strength workout needs. Visit our members-only Facebook group. Connect with like-minded people, share tips, and advice to help get closer to reaching your fitness goals. Stay strong with Jefit.

Michael Wood, CSCS

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