Intelligent Design in Training Part 4A: Repetitions, Sets, Volume, Load, & Rest Intervals
- Shane Caraway
- Apr 6
- 13 min read
Let’s begin by recognizing that repetitions are not easily examined in a vacuum; they contribute to total volume and are altered dramatically by the total number of sets, both in terms of volume and intent. They are further affected by rest intervals, all of which will be addressed independently and then holistically. Just keep in mind that the information contained here is extremely generalized since it can be so heavily altered by other variables. Where necessary, we will refer to influencing variables, but many of these ideas will be expanded upon later in their appropriate article. EDIT: Changed my mind as it is virtually impossible to address these issues independent of one another and due the subject due diligence.
NOTE: This is not a short artilcle, so those with a TikTok-level attention span are duly warned.
One of the most common questions any trainer receives is some iteration of “how many reps do I do?” Many trainers, or dare I say most, regurgitate some generalized number. More often than not, it is the “ol’ faithful” of repetition assignments: ten. All of you reading this know the near-ubiquity of the “three sets of 10” structure.
To be fair, as a general structure, 3x10 is very suitable. However, in terms of specificity, its utility begins to waiver tremendously. If, for example, your chief goal is the development of raw strength, 3x10 is horrifically inefficient. If you are an athlete seeking to develop power, it is also self-defeating and largely useless. If your goal is hypertrophy, it borders on a 5/10 scale if you’ve been training for longer than 3-6 months.
Like most generic exercise prescriptions given by mediocre trainers, once the client grows beyond that magical “beginner’s growth” stage, they also grow beyond the capabilities of the mediocre trainer. One of the reasons for this stagnation is the very different effects various repetition-set-volume schemes have on the endocrine system and neuromuscular adaptation.
Although a bit remedial for most readers, let us begin by defining our terms:
Repetition: a single exercise action, e.g., one full squat.
Set: A collection of repetitions, e.g., three sets of 10 repetitions (3x10)
Rest Interval: the time between sets to recover
Volume: The total weight lifted in a given session.
Collectively, these variables can have dramatically different adaptive stimuli. If these stimuli do not align with your training goals, you are wasting your time (and money) training in a fashion that is not optimized or efficient. This general approach may work in the earliest months of training when there is a steeper learning curve, but it also invites the inevitable “plateau.”
We don’t want that.
So let’s examine what the different adaptive responses are based on their broader, goal-oriented category: Strength, Power, Hypertrophy, and Endurance.
There are many ways to define these terms, and there is also some appreciable overlap under specific circumstances. In general, however, we define the four major adaptive goals thusly:
As you can see, differing goals require specific, purposeful program design. By manipulating load, repetitions, sets, volume, and rest intervals, we can alter the type of adaptation we will incur. Training for explosive power but doing high-loads with low rest intervals? Power will not find you.
Even more critically, each of these exercise modalities incur different adaptations, ranging from musculoskeletal adaptation to neurological, endocrine, and soft tissue. Let’s examine those as well so that we can establish a baseline understanding of the precise adaptations each training style provides.
Metabolic Adaptations
1. Capillarization - Capillarization is the expansion of existing capillaries. This enhances nutrient delivery and waste removal and is improved primarily by Endurance and high-volume hypertrophy training.
2. Mitochondrial Density - the number and volume of mitochondria within a given area or volume of muscle tissue—particularly within skeletal muscle fibers. Higher density means more mitochondria per unit of muscle fiber, increasing the muscle’s aerobic energy capacity (but not anaerobic capacity). Improved by Endurance training and high-rep circuits. No application to strength or power training.
3. Lactate Threshold Adaptation - Lactate threshold (LT) is the exercise intensity at which lactate begins to accumulate in the blood at a faster rate than it can be cleared. It marks the point where the body shifts from predominantly aerobic metabolism to increasingly relying on anaerobic pathways for energy. Improved by moderate-to-high rep training, tempo intervals. This type of adaptation does not improve strength or power, but it can be used for athletes so that the can become more resilient to fatigue and be able to draw upon their glycogen stores for those moments when explosive power is needed.
4. Buffering Capacity - The muscle’s ability to neutralize acidic byproducts, particularly hydrogen ions (H⁺), that accumulate during high-intensity exercise. It plays a critical role in maintaining muscle pH and delaying fatigue during anaerobic efforts. A critical component of anaerobic/glycolytic systems, those systems that are most crucial for strength and power primarily when time under duress exceeds 30 seconds (relays, circuits, etc). Improved primarily through Metabolic Resistance Training (MRT), Metabolic Conditioning (MetCon), and High Intensity Interval Training (HIIT).
Neural & Structural Adaptations
5. Motor Unit Recruitment (MUR): - A motor unit consists of a motor neuron and all the muscle fibers it innervates. Motor unit recruitment refers to the order and extent to which muscle fibers are activated during a contraction. Heavier loads and explosive movements recruit more motor units, especially high-threshold fast-twitch fibers. Over time, the body becomes more efficient at moving a desired load (intramuscular coordination), decreasing its perceived difficulty and reducing total energy cost. Increased MUR maximizes force and muscle activation and therefore improves strength and power (including Rate of Force Development, discussed below). Improved almost exclusively by Strength and power training, including heavy movements in excess of 85%1RM, Olympic Lifting, Plyometrics, Speed and Power-Based Drills, and Max-Effort Isometric holds.
6. Intramuscular Coordination (IC): - The synchronization and efficiency of motor unit firing within a single muscle. It reflects how well the fibers within a muscle work together to generate force. Improvements in IC enhance technical lifting and explosive output. Increases maximal force production. Is absolutely critical in developing strength and power; is mostly useless for hypertrophy. Improved almost exclusively through low-rep, high-load lifting and through heavy complex training like Olympic Lifts.
7. Rate of Force Development (RFD): - The speed at which force is produced—usually measured within the first 200 ms of muscle contraction. It is crucial for explosive actions such as sprinting, jumping, throwing, and lifting. May be understood as explosive power. The essential adaptation for all forms of athletic movement where RFD > absolute strength. Improved by Olympic Lifts,Speed-strength training (30–60% 1RM, repetitions >1.5m/s), Jump Training, Plyometrics, Ballistic Exercises (e.g., medicine ball throws).
8. Myofibrillar Hypertrophy (MH): - The growth of contractile elements (actin and myosin) inside muscle fibers. It increases fiber density and force capacity and is typically associated with strength-focused resistance training, though hypertrophy training will elicit inferior amounts (compared to sarcoplasmic hypertrophy). Increases strength and grows denser muscle tissue. Provides part of the explanation for increases in strength without concomitant increases in size (along with neurological adaptations). Gains degrade more slowly over time and are accumulative. Catalyzed through low-rep (<6), heavy loads (80–90% 1RM) training with longer rest intervals (2+ minutes). Most efficiently trained for through compound barbell movements (squat, deadlift, press).
9. Sarcoplasmic Hypertrophy (SH) - The increase in non-contractile components of the muscle cell (e.g., sarcoplasmic fluid, glycogen, enzymes). It adds volume but not necessarily strength and is the hallmark of bodybuilding/hypertrophy training. Catalyzed through moderate-load, higher-repetition training with short rest intervals (30-90s) and an overall workout design that emphasizes multiple sets per muscle per week. This prescription is not set in stone, however, as hypertrophy generally is heavily influenced through nutrition, and some data supports the notion of low-repetition hypertrophy, though this seems to diminish the more advanced the trainee is.
Endocrine/Hormonal Adaptations
Testosterone - A primary anabolic (muscle-building) hormone that influences muscle growth, strength, bone density, and neurological drive. It is naturally produced in higher levels in men, but is vital for adaptation in all athletes. Increases protein synthesis and recovery, boosts neuromuscular efficiency, supports motor unit recruitment and RFD, elevates Training Readiness. Is commonly associated with high motivation and aggression in athletes. It also supports mood and drive, and is further linked to confidence, dominance, and CNS arousal. It is difficult to overstate how critical testosterone is to all athletic and training goals. Increased through heavy Compound Lifts (≥85% 1RM, e.g., squats, deadlifts), and also by moderate-to-high volume training (6–12 reps, multiple sets) with short to moderate rest periods (60–120s).
Cortisol - a catabolic hormone released in response to physical and psychological stress. It helps mobilize energy but also promotes muscle tissue breakdown when chronically elevated. Not a friend of training generally and is a hallmark of fatigue. It breaks down larger molecules for energy (glucose and fatty acids) and is useful for short-term inflammatory response, but chronic cortisol is disastrous. Increased primarily through high-volume resistance training with minimal rest intervals (30–60 sec), and through prolonged or exhaustive training sessions. Hypertrophy work is the worst offender, but any training conducted too often without appropriate deloading or recovery protocols can tend towards elevated cortisol levels. Increases most often with moderate loads (65–85% 1RM), high reps (8–15), and short rest (30–60s) protocols, as well as with training to near-failure.
Growth Hormone (GH) - An anabolic and lipolytic hormone that supports tissue growth, fat metabolism, and the stimulation of IGF-1, a potent growth signal. Indirectly stimulates muscle growth via IGF-1. Enhances tissue repair and mobilizes fat stores for energy use post-exercise. May also support or enhance tendon and ligament remodeling.
Effects on Nervous System
Central Nervous System (CNS) - The load placed on the central nervous system from high-intensity or neurologically demanding training. This includes mental effort, motor unit recruitment, and recovery of neural drive. Over time, CNS fatigue can result in decreased neural drive, muscle activation, mood, desire to train, and poor strength expression (though actual strength does not decrease). May take days or weeks to recover if severe. The form of fatigue most common to strength and power training: max-effort lifting (90–100% 1RM), low-rep strength sets with high neural demand, Olympic lifts, heavy triples, and complex movements. The more neural drive and/or more skilled the movement, the heavier the demands on the CNS.
Accumulated/Systemic Fatigue (SF) - The overall stress load on muscular and metabolic systems over time due to training volume, frequency, rest intervals, sleep, lifestyle factors, and nutrition. It reflects how “drained” the body becomes cumulatively, not just from one session, and not just from the exercise program in isolation, but also from the stress and demands of daily life. Results in incomplete repair and dampens progress. SF degrades performance by decreasing strength and power output and leads to the dreaded “overtraining” state if left unchecked by proper deloads, sleep, and other pro-recovery methods (chief among them being not training at all for a few weeks or so). Is the bane of hypertrophy and endurance training models. Is induced by high total volume (hypertrophy training) combined with short rest intervals, frequent training without deloading, and the overutilization of failure-based sets like drop sets and myo-reps.
Connective Tissue & Skeletal Adaptations
15. Tendon Adaptation - Tendons are connective tissues that attach muscle to bone and transmit force during movement. Tendon adaptation refers to the process by which tendons become stiffer, thicker, and more resilient in response to mechanical loading—particularly slow, heavy resistance training. This adaptation improves force transmission, reduces injury risk, and enhances movement efficiency under load. Stronger tendons transfer force more efficiently, leading to more power, RFD, and maximal strength, and stiffer tendons are far more resilient to strains and ruptures. Further enhances joint stability and reduces the risk of joint injury. Tendon adaptation occurs with heavy strength training performed at a slow tempo using 3-5 sets of 3-6 reps from 70-90%1RM. The eccentric phase is especially useful and should be performed at 3-5 seconds to maximize tendon remodeling. Isometric holds from 30-45 seconds also stimulate tissue remodeling. Critically, tendons adapt to progressive overload training, like that found in strength and power training, and not with constant repetition which tends to cause or exacerbate tendonitis and tendonosis. Tendons also adapt very slowly, taking months and years of consistent training, but changes can be seen at just 8-12 weeks.
16. Ligament Adaptation - Ligaments are bands of connective tissue that connect bone to bone, stabilizing joints and guiding joint motion. Ligament adaptation refers to the remodeling and strengthening of ligaments in response to mechanical stress, particularly from resistance and functional loading. Unlike tendons, ligaments provide more passive stability, making their adaptation essential for injury prevention and joint integrity. Increased force transfer and resilience to injury naturally follow these adaptations. Ligaments are conditioned through multi-joint, compound lifts that stress major joints (e.g., squats, lunges, overhead presses), as well as Closed-Kinetic-Chain (CKC) exercise, including split squats and sled pushes. Additionally, multi-planar loading (frontal and transverse in particular) condition ligaments otherwise prone to disuse and thus to injury.
17. Bone Mineral Density (BMD): - Strengthens skeletal tissue and prevents osteoporosis and generally strengthens bones. Improved through high-impact and heavy resistance training.
As you have likely inferred, heavy training is the ideal means of improving the strength and resilience of ligaments, tendons, and bones. Power is the runner-up, with hypertrophy third, and endurance training offering the least. Note that many hypertrophy protocols are also Endurance-based. Review the following:
Training Type | Effect on Tendons | Effect on Ligaments |
Strength Training (e.g., 1–6 reps @ ≥85% 1RM) | Strongest remodeling due to high load & slow contraction speeds | Progressive overload enhances ligament stiffness |
Power Training (e.g., 3–5 reps @ 30–60% 1RM, fast tempo) | Moderate tendon load via explosive contractions | Some ligament adaptation, especially with plyos |
Hypertrophy Training (6–12 reps @ 65–85% 1RM) | Moderate remodeling via volume and metabolic stress | Low-to-moderate stimulus, mainly through load exposure |
Endurance/High-Rep Training (12–20+ reps @ <65% 1RM) | Minimal tendon response | Minimal ligament response |
The Role of Rest Intervals & Energy Pathways
Rest Intervals (RIs) are an integral component to the overall set/rep/volume matrix and can directly alter the adaptive stimulus. An arbitrary Rest Interval indicates an inferior training program and an ignorant trainer. Somehow, RIs remain the most elusive component for mediocre coaches to emphasize despite its upending potential, and any program that fails to target the desired energy system is a profound disservice to an athlete or anyone with serious goals.
18. Strength Training - Strength training generally follows RIs ranging from 2-5 minutes, sometimes even greater RIs when training for competition. Strength is expressed most often in very short bursts utilizing the ATP-PC (Adenosine Triphosphate-Phosphocreatine; anaerobic alactic system). This “rocket fuel” of sorts is exhausted after 20 seconds (or less), requiring longer rest periods to fully replenish phosphocreatine stores. Insufficiently-long RIs mean that neural drive and phosphocreatine stores cannot be replenished, meaning that the next set or attempt is sub-maximal and cannot efficiently drive the desired adaptations. Insufficient rest also risks transitioning to undesired energy systems, primarily glycolytic. Unsurprisingly, the ATP-CP system is enhanced by the same type of training that utilizes it as a principal substrate.
19. Power Training - Focuses on explosive performance and Rate of Force Development (RFD) maintenance. Typically employ RIs of 2-3 minutes and depend on both the ATP-PC and Glycolytic systems (or anaerobic glycolysis, which we’ll call AG). AG begins at approximately 10 seconds of high-intensity output when the ATP-CP pathway can no longer produce sufficient ATP (energy) to sustain the action. AG may remain the primary energy pathway for up to two minutes before the body changes to aerobic systems. Maintaining a 2-3 minute RI allows sufficient recovery to maintain velocity and coordination in lifts while still generating systemic demand. AG can be improved through block-style training, HIRT protocols, or HIIT protocols, depending on purpose, so that energy pathway training can be specific to the goals of the client.
20. Hypertrophy Training - Focuses on the AG system to induce metabolic stress, cell swelling, and GH secretion. To these ends, RIs are generally 30-90 seconds. These shorter RIs
maintain muscular tension, elevate lactate and GH levels, and induce sarcoplasmic hypertrophy. RIs in excess of 90s risk losing the hypertrophy-inducing effects given by shorter RIs.
21. Endurance Training - Depends on the Oxidative (aerobic) and aerobic glycolytic systems. Endurance work utilizes RIs less than 30 seconds to enhance fatigue resistance, aerobic efficiency, and metabolic conditioning. It accomplishes this by keeping the heart rate elevated, improving buffering capacity, and training muscles to function under sustained fatigue.
Evidenced by the length and depth of this article, Repetitions, Sets, Load, Volume, & Rest Intervals all heavily influence what adaptive responses we will enjoy from the sweat of our labor. With so many critical components, the probability of improper program design increases, and the fallacy of “winging it” becomes a recipe of self-sabotage. Even worse, trainers who are unversed and unskilled on these program variables risk the time and treasure of their clients, an abuse of their duties and the trust of their clients. This most often emerges when the honeymoon phase of training is over and the generic “3x10” without careful RIs ceases being a universal tool for advancement and development.
Sources
1. Schoenfeld, B. J., Grgic, J., Ogborn, D., & Krieger, J. W. (2017).
Strength and hypertrophy adaptations between low- vs. high-load resistance training: A systematic review and meta-analysis.
Journal of Strength and Conditioning Research, 31(12), 3508–3523.
2. Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2016).
Effects of resistance training frequency on measures of muscle hypertrophy: A systematic review and meta-analysis.
Sports Medicine, 46(11), 1689–1697.
3. Krzysztofik, M., Wilk, M., Wojdała, G., & Golas, A. (2019).
Maximizing Muscle Hypertrophy: A Systematic Review of Advanced Resistance Training Techniques and Methods.
International Journal of Environmental Research and Public Health, 16(24), 4897.
4. Baechle, T. R., & Earle, R. W. (2008).
Essentials of Strength Training and Conditioning (3rd ed.). NSCA – National Strength and Conditioning Association.
5. Cormie, P., McCaulley, G. O., Triplett, N. T., & McBride, J. M. (2009).
Acute hormonal and neuromuscular responses to hypertrophy, strength and power type resistance exercise.
European Journal of Applied Physiology, 107(1), 1–11.
6. Kongsgaard, M., Reitelseder, S., Pedersen, T. G., Holm, L., Aagaard, P., Kjær, M., & Magnusson, S. P. (2007).
Region specific patellar tendon hypertrophy in humans following resistance training.
Acta Physiologica, 191(2), 111–121.
7. Bohm, S., Mersmann, F., & Arampatzis, A. (2015).
Human tendon adaptation in response to mechanical loading: A systematic review and meta-analysis.
Sports Medicine – Open, 1(1), 7.
8. Wernbom, M., Augustsson, J., & Thomeé, R. (2007).
The influence of frequency, intensity, volume and mode of strength training on whole muscle cross-sectional area in humans.
Sports Medicine, 37(3), 225–264.
9. Kraemer, W. J., & Ratamess, N. A. (2005).
Hormonal responses and adaptations to resistance exercise and training.
Sports Medicine, 35(4), 339–361.
10. Hackney, A. C. (2006).
Stress and the neuroendocrine system: The role of exercise as a stressor.
Sports Medicine, 36(8), 695–705.
11. Haff, G. G., & Nimphius, S. (2012).
Training Principles for Power Development.
Strength and Conditioning Journal, 34(6), 2–12.
12. Brooks, G. A. (2001).
Lactate doesn't necessarily cause fatigue: Why are we surprised?
American Journal of Physiology-Endocrinology and Metabolism, 280(5), E744–E745.
13. Edge, J., Bishop, D., Goodman, C. (2006).
The effects of training intensity on muscle buffer capacity in humans.
European Journal of Applied Physiology, 96(1), 97–105.
14. Harris, R. C., Tallon, M. J., Dunnett, M., Boobis, L., Coakley, J., Kim, H. J., & Sale, C. (2006). The absorption of orally supplied beta-alanine and its effect on muscle carnosine synthesis in human vastus lateralis. Amino Acids, 30, 279–289.
15. Issurin, V. B. (2008).
Block periodization versus traditional training theory: a review.
Journal of Sports Medicine and Physical Fitness, 48(1), 65–75.
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