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Heuristics for fitness

17 min read

If you have a lot of time and want to check references or explore based on topic, read the Wikipedia article on Strength Training for research, and the Fitness Subreddit Wiki for routine and nutrition advice. This blog post overlaps heavily with advice found there, but aims to be a personal summary of information from 2+ years of research, 10+ years of personal exercise experience, and 1+ years of coaching experience. If you, dear reader, see any claims that have been falsified or outdated, please reach out!

Being “fit” takes different forms for different people, but exercising in the right way can reduce the risk of severe injury, increase freedom of movement, and enjoyment of the same. You likely live longer and happier if you are exercising regularly [0].

Resistance training

The most efficient way to exercise for general movement ability and health is Resistance Training [1]. It is also most effective at increasing muscle mass. Muscle mass is one of the most important vital signs when it comes to health in all ages [1].

Changes to your bone and muscle structure are also important and can be developed independent of the actual muscle. Bone and muscle structure changes occur over years of training. Tendon and bone strength increase over months to years [2,3]. Muscle size increases over weeks and months. Fiber recruitment improvements occur over days. Especially in old age, bone and tissue strength increases significantly and reduces injury risk.

If your goals are beyond regular health, you are competitive, or want to progress in certain sports or disciplines, the type, amount, and methods of exercise will vary heavily.

Finding a training regimen

The most efficient way to do resistance training for people who just want to be healthy and dislike exercising is to train 2 times a week for ~60 minutes, and to follow the rules below. The most effective way (not recommended for beginners) is to train up to 6 times a week for up to two hours each, and follow the same rules. Generally, weekly training volume matters more than training frequency [4], with the jump from 1 to 2 sessions per week being the most significant [5]. As you get fitter, you can recover faster from more strenuous exercise, requiring you to add more sessions or volume for further development.

Adherence is key to get the most out of resistance training. It matters most that you exercise, not how hard or how often. That said, once you do go regularly, the following guidelines make exercising much more effective and efficient, whether you go to the gym, do bodyweight exercises, or train as part of a sport that includes resistance exercises:

Before you start exercising regularly, find your exercises: Find a set of 5-10 exercises that, together, cover most of your muscles, and stick to those for at least a few months. See further below for examples. You’ll be tempted to experiment with different exercises: don’t, unless it is to avoid pain in specific exercises.. Then find your level: For each exercise, find a weight amount or progression that’s just heavy enough so that you get exhausted doing 10-20 repetitions of it. This is your starting weight. See “Doing an exercise” below for how to do each rep, and the section about “goals and metrics” further below for specific recommendations of how many repetitions and sets to do.

Training sessions

Before an exercise session, do not stretch or do cardio [6]. Stretch after if desired, and limit cardio to off-days. Instead, perform a once-per-session general warmup by getting your body warm (in terms of temperature), e.g. doing a single set of bodyweight squats, 5 minutes of brisk walking, or 2 minutes of light jogging.

Then, for every exercise on your plan, do the following:

  • Specific Warm-up: Perform the exercise you’re about to do without any weight for 10+ reps, in a slow and controlled manner, using full range of motion. This should be very easy, and will adequately warm up the specific muscles you need for that exercise [4]. Take a minute break before starting your actual exercise. The older you are, or the more weight you intend to lift during your session, the more important this will be.
  1. Performing sets: Start doing repetitions with your current weight, without pause, in smooth, continuous, slow motions. See the section “Range-of-motion, form, reps, and body mechanics” below for more information on how to perform a rep. Stop as soon as you are no longer able to maintain controlled, smooth motions. If you don’t reach your desired amount of reps, do not take a tiny break and then do the rest. Stop the set and use less weight next time.
  2. Do 3-5 sets (more is better, depending on how much time you have) and take about 2 minutes of rest between each set. Less is ok, more is better but time-inefficient (slight benefits up to 3 minutes, fleeting benefits up to 5 minutes) [7]. See “Rest time” below for more information and tips on cutting down rest time. Some exercises are unilateral, where you perform the exercise on one side of the body, and then the other. Take a short rest in between them for your heart/breath to recover. Together they’re one set, and a break between sets should still be taken.
  3. Switch to the next exercise in the list. If your session is 60 minutes, you should be able to do about 4-6 exercises. See below for an example of scheduling.
  • Adjusting weights: If you manage to do more than 20 reps, increase the weight for the next set or session so that you land in the 10-20 rep range again. This way, you will slowly progress in weight. Staying in this range while progressively increasing weights is the safest way to reliably increase muscle mass and strength. If you’re doing body-weight exercises like pushups and exceeding 30 reps with good form (advanced level), it’s not easily possible to increase weight, so instead switch to a similar, but more difficult exercise, like e.g. pike pushups in the case of regular pushups. Or, if you are short of 10 reps, try making the exercise easier, e.g. knee-supported pushups in this case.

When picking an exercise, choose exercises with higher injury risk or more full-body engagement first. This reduces injury risk by making sure you’re not too exhausted to perform the critical exercises with good form, while still allowing you to completely exhaust your muscles in the later, more specific exercises.

Rest time

In the above program, at least half of your time is spent resting. This can take a significant amount of time. The reason we rest up to 2+ minutes is so that the specific muscles can fully recover and your cardiovascular system is not challenged heavily. Otherwise, following sets of the same exercise don’t adequately engage the muscle anymore [7].

If your breathing and heartbeat recover sooner than 2 minutes after a set, you can start to reduce overall rest time by performing super-sets for efficiency [4], which means interleaving 2+ exercises of different muscle groups, e.g. doing a set of squats, then rest for 30s (or however long it takes for your breath to come to a normal pace), then a set of overhead presses, then rest 1+ minutes. This allows the specific muscles to rest for 2+ minutes, while still cutting down significantly on time spent.

If you have a particularly strong cardiovascular system and your experience with specific exercises increases, it can start to make sense to interleave 3 exercises, with only minimal break in between each set. The main difference between this and a high-intensity interval training (HIIT) is that you still focus mainly on strength and muscle gain, vs. just on overall cardio, by making sure that you perform exercises only to the point where you don’t challenge your endurance, while making sure that each exercise is performed to muscular failure over many sets.

Example exercises and schedules

  • As a beginner in the gym, you could train for two sessions per week, 60 minutes each, e.g. Monday and Thursday. You should favor machines as they reduce injury risk for early beginners.
  • As an intermediate in the gym (2-12 months experience, depending on your baseline), with three sessions per week (e.g. Monday/Wednesday/Friday), your muscles need more stimulation to grow, so we split days to focus on specific muscle groups. You should also focus more on compound (multi-joint) and free-weight movements, as they improve general athleticism and freedom of movement more than machine exercises.
    • Day 1 (Push): Bench press, shoulder press, lateral raises, triceps extensions, external shoulder rotations, internal shoulder rotations
    • Day 2 (Pull): Pull-ups (or lat pull-downs), dumbbell rows, face pulls, bicep curls, shrugs, leg raises (or ab crunches), back extensions
    • Day 3 (Legs): Squats, Romanian deadlifts or leg curls, lunges or Romanian split squats, leg abduction and adduction machine, calve raises, tibialis raises
  • As an intermediate in calisthenics (2-12 months experience in the gym or doing basic bodyweight exercises), with access to rings.
    • Day 1 (Push): Pike pushupsRing pushups, ring chest fly, ring dips, ring triceps extensions
    • Day 2 (Pull): Ring pull-ups or chin-ups, ring rows, ring reverse fly, ring bicep curls, shrugs, ring leg raises
    • Day 3 (Legs): Deep step-ups or pistol squats, Bulgarian split squats, single leg hip thrusts, plyometric box jumps

Range-of-motion, form, reps, and body mechanics

If you perform an exercise for as many repetitions as you can with good form, and you just barely, barely, manage to squeeze out the last rep, that is called “training to failure”. Training to muscular failure does not help increase muscle mass, and is also not harmful. The most efficient way to train is to stop 2-3 reps short of failure (same muscle gain, less effort). I would advise training to failure some of the time, to re-calibrate yourself on how many reps you can actually do, and start subtracting 2-3 reps again.

To get the most out of every single exercise and every single repetition, proper form is essential. Performing reps with full range of motion (ROM) increases (or at least maintains) mobility while also increasing hypertrophy. Most exercises are designed to target specific joints and their supporting muscles at specific axes. Full ROM means moving the joints all the way between their flexed position and their extended position. E.g. for a bicep curl, this would mean getting your forearms into a straight line with the upper arm, then curling as high as absolutely possible, before lowering all the way to straight again.

Performing reps at a timing of 31X0 seems to be most efficient for high hypertrophy [4], with significant gains in mobility and strength. “31X0” specifically means taking 3 seconds for the eccentric, resting 1 second at the most stretched position, performing an explosive concentric, and then resting 0 seconds before starting the next rep (see Wikipedia on how to read timings). For a pushup, this would mean lowering down 3 seconds, waiting 1 second without resting your body on the ground, then coming back up as quickly as possible (without breaking form). Note, however, that for pull-ups, the eccentric starts at the top. To figure out which is the eccentric, think about which part of the movement returns the weight to its natural resisting position.

Exercises should be designed so that muscles can resist at constant force or resist more heavily at the end range of motion. A standing bicep curl, for example, will see the heaviest load at the middle of the motion, since the forearm is perpendicular to the upper arm, which generates the most angular momentum for the biceps to resist against. This means machine biceps curls, which are angled at ~45 degrees at the start of the motion, are slightly more effective, as they shift the load curve during the exercise toward the end range of motion. For the same reason, using a band to assist with pull-ups will lead to the opposite of the optimal load curve, because it helps most at the start of the movement, and least at the top of the moment.

Movements targeting a specific joint or muscle should not require the injury risk to be set by other, unrelated muscles. For example, dips have a high injury risk because, at the deepest point, many auxiliary shoulder muscles that are not ordinarily exercised need to work hard to maintain stability. When weight is progressed and these smaller muscles become the bottleneck, injury risk is heightened. This is another reason to use full ROM from the beginning, so these smaller muscles have time to adapt. Complex exercises like dips should be either supplemented with specific training for auxiliary muscles, or be done with high focus and rigorous control towards the end ranges to minimize injury risk.

Similarly, complex exercises should be done in a way that linearly loads specific muscles over full ROM. A pushup, for example, will linearly load your chest and triceps. Not maintaining proper form, by e.g. caving in your chest and arms at the bottom before getting back up, will briefly and suddenly engage your neck, shoulders, and spine muscles in a weak position, and short ROM, while also shortening the ROM of your chest and triceps. Doing deep pushups on parallel bars allows loading the same auxiliary muscles in a controlled and linear fashion with higher ROM, actually training the muscles and reducing injury risk in the long term.

Periodization and fatigue

Aside from muscle strain and cardiovascular strain, your central nervous system (CNS) also accumulates fatigue. The lower the rep range you train with, and the more full-body exercises you do, the higher the strain on your CNS. Your CNS recovers much more slowly than your muscles. For this reason, it is recommended to schedule training plans to have recovery (de-load) weeks, where every 4-8 weeks (depending on how much strain is accumulated) one week consists of no or very low-strain exercise (e.g. half the weight and half the reps, for each exercise).

Similarly, in order to train both strength and hypertrophy, choosing a periodization with lower and lower rep ranges every week, followed by a recovery week, before resetting to the highest rep range, is common in training for long-term strength (over muscle size), for many sports and weightlifting disciplines.

Fatigue also accumulates from eating at a caloric deficit. All training is most effective when done at a slight caloric surplus, with adequate protein intake.

Atrophy and sustainability

De-training: muscles start to atrophy after 2-3 weeks of not being used in significant volume. A rule of thumb for “significant volume” is doing your regular training plan at about half your usual volume, at half your usual reps, and at half the weight. Bed rest (e.g. due to hospitalization) speeds up atrophy. Strength loss starts after 3-4 weeks. Endurance loss after 3-4 weeks. Endurance declines less for beginners [8]. Muscles that have been built and trained over many years will atrophy at the same speed, but come back more quickly (e.g. after 5 years of training, 1 year of not training could feasibly be recovered by training 1-2 years again).

Caloric deficit: Eating less than your body requires, especially if you’re eating low protein, will cause a loss of muscle mass. This is usually well-regulated by the body, increasing hunger as the need for calories increases, but eating foods high in fiber or protein will reduce hunger, possibly setting your baseline lower than required for maintaining muscle.

Cardio and sports

Most sports and cardiovascular training routines are generally beneficial for health. While only slightly decreasing injury risk, cardio decreases cardiovascular risk factors more than resistance training. Resistance training 4+ hours a week counts as light cardio for this metric. It is not too late to start dedicated cardio (though endurance sports) in old age, where cardiovascular health risks are greatest, and meaningful changes can be made over months.

Sustained, long-term high-volume cardio (4-12+ hours per week) can lead to 20-40% lower all-cause mortality in old age [9], and all volumes of cardio may "improve mental health, including reducing stress and lowering the incidence of depression, as well as increased cognitive capacity" [wikipedia]. For most younger individuals, the physical and mental benefits are less pronounced, but likely still worth pursuing.

Goals, metrics, and training styles

Strength: While strength and muscle size are strongly related, you can train strength without significantly increasing muscle size. Training in a rep range of 4-6 with adequately heavy resistance, and using longer rest times, will disproportionately favor strength gain over muscle size gain [10]. Someone new to strength training can expect to double their weight on most resistance training exercises without gaining significant muscle. To go beyond this, adding muscle is required. Strength-specific training is not advised for beginners, because of the higher risk of injury.

  • More specifically, strength is a factor of muscle cross-sectional area (size, hypertrophy), motor unit recruitment (number of muscle fibers recruited in the movement), motor rehearsal (how efficient you are at coordinating between muscle sections and groups, a.k.a. muscle memory), preferential fiber typing recruitment (order in which fibers are recruited to perform the movement)
  • Bigger muscles have better tendon insertion angles (since the tendon is at the center), which also is very dependent on genetics, and plays a large role in max. relative strength to weight ratio.

Hypertrophy: Increasing muscle size also increases strength. Having more muscle also affects the maximum strength you can expect to gain from strength training. Training in a rep range of 10-30 with adequately heavy resistance and as many sets as possible is most effective for hypertrophy. The higher end of the rep range is slightly more effective, because your muscles recover from sets faster, allowing you to do more sets, but this takes more time overall. Training around 12-15 reps is most time efficient in my experience.

Explosiveness: Explosive movement helps train your central nervous system to recruit the largest muscle fibers sooner and more completely (recruitment order and rate coding). Strength training with proper repetition timings adequately increases explosiveness for most use cases, but if explosiveness is the express goal, adding e.g. plyometrics to your routine might help. This is because slightly more of the strength gain happens for the specific velocity at which the training happens [11].

Flexibility: Stretching increases passive flexibility: the range that your muscles can stretch to. Flexibility alone does not usually decrease injury risk, but can increase ROM that is lost to aging or reduced by performing resistance training with limited ROM. If you are playing sports, there are likely sport-specific stretching routines that are advised to perform after the sports session to maintain or expand flexibility.

Mobility: This is the ability to exert strength in flexed positions, also known as active flexibility. Stretching improves this to some extent, but training muscles primarily in stretched positions with added resistance helps more. Mobility reduces injury risk directly by preventing tissue tearing when your body is in compromised positions. Many muscles that are important for mobility are under-worked in regular resistance training and are usually prescribed as exercises for physical therapy, but it is easier to address proactively than to recover from an injury. These exercises include rotator cuff exercises, like internal and external shoulder rotationship abduction and adduction, tibialis raises, and wrist and ankle mobility exercises.

Functional Training: A buzzword with unclear definition, often used as a synonym for mobility. Any training that meaningfully aids in performing a specific function is functional, so the applicability of the term comes down to what you consider to be a useful function to train for. The term is also often used in rehabilitation: having enough hip mobility to stand up from a toilet without having to use your hands is functional, and training for it is functional training.

Bodyweight Training: Often refers to resistance training without weights, or is seen as a regression for weighted exercises. Advanced bodyweight fitness is synonymous with calisthenics, which emphasizes gaining the required strength and mobility to perform more and more difficult skills. A major difficulty with bodyweight exercises is the inability to properly regress or progress exercises. For some movements, adding weight to bodyweight exercises is a perfectly valid form of progression.

High-Intensity Interval Training (HIIT): Results in lower muscle and strength gain than resistance training, but is more effective at inducing autophagy than resistance training or lower-intensity cardio [12]. The benefits seem to be most pronounced in beginners, and similar results can be reached in the long run via high-intensity resistance training combined with cardio.