Key Takeaway
Progressive overload means making your training harder over time, and load is only one of seven levers you can pull. Controlled research shows that adding reps at a fixed weight builds the same muscle as adding weight at fixed reps. The full toolbox: load progression, rep progression, set progression, tempo control, range of motion progression, rest manipulation, and density training. Pick one lever per lift, track it ruthlessly, and switch levers when one stalls. Lifters who understand this keep progressing for years after the "add 5 lb every week" crowd hits a wall.
Progressive overload is the closest thing lifting has to a law of physics. Muscles grow and get stronger when you force them to do more than they are accustomed to, and they stop adapting the moment the demands stop increasing. Every program that works -- push/pull/legs, upper/lower, full body, 5/3/1, whatever -- works because it delivers progressive overload. Every program that fails, fails because it stopped delivering it.
The problem is that somewhere along the way, "progressive overload" got flattened into "add weight to the bar." That works beautifully for about six months. A beginner's nervous system adapts so fast that weekly load jumps are sustainable, and the linear-progression programs built on that fact deserve their reputation. Then the easy gains run out, the 5 lb jumps start failing, and a huge number of lifters conclude they have hit their genetic ceiling when what they have actually hit is the limit of one progression method.
The research is clear that load is just one dimension of overload. In 2022, Plotkin and colleagues ran a direct test: one group progressed by adding load at fixed reps, another progressed by adding reps at a fixed load. After eight weeks in trained subjects, muscle growth was essentially identical between groups. The muscle does not read the number on the plate. It responds to tension, effort, and total work, and there are multiple ways to increase each.
This guide covers all seven progression methods, the evidence behind each, where each one shines, and a simple framework for combining them so you always have a next move.
What Progressive Overload Actually Means
The principle traces back to the (probably apocryphal) story of Milo of Croton, who carried a calf every day until it became a bull. The formal version: for continued adaptation, the training stimulus must increase over time as the body adapts to the current workload.
Mechanistically, the primary driver of muscle growth is mechanical tension -- force experienced by muscle fibers while they produce force, especially under stretch and close to fatigue (Schoenfeld, 2010). Strength adds a neural component: your nervous system learning to recruit more muscle, more efficiently, in a specific movement. Both adaptations respond to demands that exceed what the body is currently prepared for.
Here is the part that unlocks everything else: "demand" is multidimensional. A set of 8 with 200 lb taken to 1 rep shy of failure is a demand. So is a set of 12 with the same 200 lb three weeks later. So is a fourth set where there used to be three, a deeper squat at the same weight, or the same workout completed in 45 minutes instead of 60. Your muscles experience all of these as more than they did before. Each one is overload.
That gives you seven practical levers:
- Load: more weight, same reps and sets
- Reps: more reps, same weight
- Sets: more total sets per muscle per week
- Tempo: more controlled time under tension per rep, same weight
- Range of motion: more distance and more stretch per rep
- Rest: same performance with less recovery between sets
- Density: more total work in the same training time
One condition applies to all seven: effort has to be real. Overload only exists relative to your current capacity, which means sets need to be taken reasonably close to failure -- in the 0-4 reps in reserve range for most hypertrophy work. Adding a fifth set you sleepwalk through is volume on paper and nothing in the muscle.
Why "Just Add Weight" Stops Working
Load progression fails first for a simple mathematical reason: the jumps stay fixed while your capacity to improve shrinks.
When you squat 95 lb, adding 5 lb is a 5.3% jump, and a beginner's week-to-week adaptation can cover it. When you squat 315 lb, that same 5 lb is 1.6%, and even that outpaces what an intermediate gains in a week. On small lifts it is worse. Adding 5 lb to a 30 lb lateral raise is a 17% increase. No deltoid on earth adapts 17% in a week, which is why pressing and isolation movements stall years before squats and deadlifts do.
The second failure mode is sneakier: fake overload. When the weight goes up but your squat gets two inches higher, your rows get more violent, and your bench reps start bouncing, you did not overload the muscle. You changed the exercise into an easier one and kept the same number on the bar. The logbook says progress; the muscle experienced less tension through less range. This is rampant, it is the main engine of ego lifting, and it is why two lifters with identical logbooks can have completely different physiques.
The third issue is context. In a calorie deficit, recovery capacity drops and forcing load progression mostly degrades technique. During high-stress weeks, with poor sleep, or in your forties, the weekly-PR model breaks down. The lifters who keep progressing are the ones with more than one lever to pull.
The Plateau Is Usually Upstream
Before blaming your progression scheme, audit the basics. Chronic sleep debt, inadequate protein, a too-aggressive deficit, and skipped deloads stall more lifts than programming ever will. No progression method outruns a recovery problem. If everything stalled at once, the answer is rarely a new rep scheme.
Method 1: Load Progression (Done Right)
Adding weight is still the foundation, and for maximal strength it is irreplaceable. Strength is specific: if you want a bigger squat, bench, or deadlift, you eventually have to handle heavier weights in those lifts. Load also has the cleanest long-term signal -- over months and years, the bar going up is the least ambiguous evidence that you are a more capable lifter.
Doing it right means respecting the math from the previous section:
- Match the jump to the lift. 5-10 lb jumps belong on squats and deadlifts. Benches and overhead presses do better with 2.5-5 lb. Isolation work often cannot handle the smallest plates in the gym, which is exactly when you switch to rep progression instead.
- Microload where it matters. Fractional plates (0.5-1.25 lb) cost almost nothing and turn an impossible 17% dumbbell jump into a sequence of manageable ones. For pressing lifts past the beginner stage, they are one of the best purchases in lifting.
- Hold every other variable constant. Load progression only counts when depth, tempo, and rest stay the same. Same lift, more weight. Different lift, meaningless comparison.
- Expect the timescale to stretch. Beginners add load weekly. Intermediates add it monthly on big lifts. Advanced lifters measure load progress across entire training blocks. None of those lifters is failing; they are at different points on the same curve.
Best for: compound barbell lifts, strength-focused goals, beginners on linear progressions, and any lift where the percentage jump stays small.
Method 2: Rep Progression
If load progression is the foundation, rep progression is the workhorse that carries everyone past the beginner stage. The evidence here is unusually direct. Plotkin et al. (2022) assigned trained lifters to either load progression (add weight, keep reps) or rep progression (add reps, keep weight) for eight weeks. Hypertrophy was essentially the same in both groups, and strength improvements were broadly similar, with load progression holding an edge mainly on maximal-strength specificity. For muscle growth, a rep added is worth as much as a plate added.
This makes sense mechanistically. Within the roughly 5-30 rep range, sets taken close to failure produce comparable hypertrophy per set. Going from 8 reps to 11 reps with the same weight means you produced more total work and reached the same high-tension final reps -- the stimulus went up, no new plates required.
Double Progression: The Default That Should Be Everyone's Default
The cleanest implementation is double progression: pick a rep range, add reps inside it, and add load only when you max the range out. It automatically delivers correctly-sized load jumps, since you only earn a weight increase after proving capacity at the top of the range.
| Week | Weight | Sets x Reps (range 8-12) | Action |
|---|---|---|---|
| 1 | 100 lb | 3 x 8, 8, 7 | Stay. Build reps. |
| 2 | 100 lb | 3 x 10, 9, 8 | Stay. Build reps. |
| 3 | 100 lb | 3 x 11, 11, 10 | Stay. Almost there. |
| 4 | 100 lb | 3 x 12, 12, 12 | Range maxed. Add weight. |
| 5 | 105 lb | 3 x 9, 8, 8 | Cycle restarts. |
Wider ranges (8-15, even 10-20) suit isolation lifts and machines, where each rep is a smaller fraction of the total and load jumps are proportionally huge. Narrower ranges (4-6, 6-8) suit heavy compounds. The principle is identical.
Best for: dumbbell work, isolation lifts, machines, anyone past the newbie phase, and every lift where the next available weight jump is too big.
Method 3: Set Progression
The first two methods make individual sets harder. Set progression increases how many hard sets a muscle gets per week, and weekly hard sets are one of the best-documented dose-response relationships in training research. The Schoenfeld, Ogborn, and Krieger (2017) meta-analysis found that more weekly sets produced more hypertrophy, with 10+ sets per muscle per week clearly outperforming fewer. We covered the full dose-response picture, including where it bends, in our training volume guide.
The practical structure comes from the volume landmarks popularized by Dr. Mike Israetel: start a training block near your minimum effective volume, add sets gradually as your body adapts, approach your maximum recoverable volume by the end of the block, then deload and reset. A typical mesocycle for a priority muscle might run from 12 weekly sets in week 1 to 18-20 by week 5.
Two warnings keep this method honest. First, volume is the easiest lever to overdo. Sets you add past your ability to recover do not build extra muscle; they generate fatigue that degrades the sets that were working. The junk volume threshold is real and it arrives sooner than enthusiasm suggests. Second, set progression has a structural ceiling that load and reps do not. You cannot add sets forever -- which is why it works best as a within-block tool that resets each mesocycle rather than a permanent staircase.
Where the New Set Goes Matters
Add sets to the muscle, not necessarily the lift. If your bench has stalled at 5 weekly sets of pressing, a 6th set of bench may serve you worse than 2 new sets of incline dumbbell press. Same weekly pressing volume increase, fresher joints, and a slightly different stimulus. Set progression pairs naturally with exercise variety.
Best for: hypertrophy blocks, lagging muscle groups, intermediate and advanced lifters structuring mesocycles, and anyone whose per-set progression has stalled while recovery capacity still has headroom.
Method 4: Tempo Manipulation
Time for some honesty, because tempo is the most oversold method on this list. The Schoenfeld, Ogborn, and Krieger (2015) meta-analysis on repetition duration found similar hypertrophy across rep durations anywhere from 0.5 to 8 seconds, while deliberately super-slow training (10+ second reps) produced inferior results. Slowing your reps down is not a secret growth multiplier. A later review by Wilk and colleagues (2021) reached a compatible conclusion: within a broad range, tempo matters far less than effort and proximity to failure.
So why is it on the list? Because tempo has two legitimate jobs.
Job one: making a fixed load harder when you cannot add weight. If your equipment tops out -- the classic home gym problem -- taking your 50 lb dumbbell press from a 1-second to a 3-second eccentric meaningfully increases the work each rep demands, and your rep count at that weight drops accordingly. You have re-created room to progress with the same hardware. Pause reps work the same way: a 2-second pause at the bottom of a squat or bench removes the stretch reflex and makes the same bar weight harder.
Job two: measurement integrity. This is the unglamorous one that actually matters for everyone. Progression only means something if reps are comparable across sessions. The lifter whose reps get faster, bouncier, and shorter as the weeks pass is not progressing; they are cheating the measurement. Standardizing a controlled eccentric (around 2 seconds) and a crisp concentric makes every logged rep the same unit. Most lifters who think they need a fancier progression scheme actually need this.
Best for: equipment-limited training, joint-friendly progression during injury management, breaking through sticking points with pauses, and enforcing honest rep standards everywhere.
Method 5: Range of Motion Progression
Range of motion is the most physical form of overload: more distance per rep at the same weight equals more mechanical work, and deeper positions load the muscle at longer lengths, where the hypertrophy stimulus appears strongest.
The research supports full ROM as the general rule. Reviews by Schoenfeld and Grgic (2020) and Pallarés et al. (2021) found full range of motion generally superior to shortened, lockout-style partials for muscle growth, particularly for lower body lifts. More recent work adds an interesting wrinkle: training at long muscle lengths seems to be doing much of the work. Maeo et al. (2021) found roughly 50% greater hamstring growth from seated leg curls (hamstrings stretched) versus lying leg curls (hamstrings shortened), and Pedrosa et al. (2022) found that partial reps performed in the stretched position matched or beat full ROM for quad growth. The pattern across these studies points the same direction: the stretched half of the movement is where the money is.
As a progression method, ROM works in steps:
- Earn full range first. If your squat is high or your presses stop short, progressively deepening at the same load is real overload, the same as adding weight. Half-squat 225 to full-squat 225 is progress no logbook number captures.
- Then extend past "full." Deficit Romanian deadlifts, deficit push-ups, heels-elevated squats, and full-stretch cable flyes load positions standard lifts never reach. Same weight, new stimulus.
- Use lengthened partials when full ROM breaks down. At the end of a hard set, reps confined to the stretched half extend the set in its most productive region. The partials to avoid are the opposite kind -- the top-half ego reps that skip the stretch entirely.
Standardize Before You Progress
ROM cuts both ways. If your range silently shrinks as weights climb, your apparent load progression is partly fake. Film your top sets occasionally, pick fixed depth standards (touch points, pins, boxes), and treat any rep that misses the standard as a rep that did not happen. Only then does deliberately extending ROM count as progression rather than noise.
Best for: lifters whose ROM has quietly eroded, equipment-limited training, hypertrophy work on stretch-responsive muscles (hamstrings, quads, pecs, calves), and adding a new stimulus without new weight.
Method 6: Rest Period Manipulation
Rest manipulation needs the most careful handling, because the naive version backfires. Shortening rest periods makes training feel brutally harder, and it is tempting to read that difficulty as stimulus. The research says otherwise for primary work: Schoenfeld et al. (2016) found that 3-minute rests produced more strength and more muscle than 1-minute rests in trained men, because longer rest preserved performance on subsequent sets. Cutting rest cut the total work done, and the muscle responded to the work, not the discomfort.
So the rule for your main lifts is boring: rest 2-5 minutes, long enough to perform. Rest manipulation becomes a genuine progression tool under one strict condition -- performance holds constant while rest shrinks. If you complete 3 x 10 with 100 lb on 3 minutes of rest today, and two months from now you complete the same 3 x 10 with 100 lb on 2 minutes of rest, you have improved. Specifically, you have built work capacity: better inter-set recovery, better conditioning, more training fitness. That adaptation compounds, because a lifter who recovers faster between sets can productively handle more volume per session forever after.
Where deliberately short rest belongs from day one: accessory and isolation work, where systemic fatigue is low and some performance loss is acceptable; muscular endurance goals; and conditioning-adjacent training. Where it never belongs: heavy compound sets you are trying to progress on, especially squats and deadlifts.
Best for: building work capacity, time-pressed sessions, accessory work, and lifters whose load/rep/set levers are all moving fine but who want a measurable fitness dimension to push.
Method 7: Density Training
Density is rest manipulation's more practical sibling: total work divided by total time. Instead of obsessing over individual rest periods, you measure the session. Same workout in less time, or more workout in the same time -- either direction is overload, and for anyone training inside a lunch break, it is the progression method that respects reality.
The useful tools:
- Antagonist paired sets. Alternate opposing movements (bench/row, curl/pushdown) with short transitions. Robbins et al. (2010) found paired sets maintain performance while cutting session time dramatically -- one of the few free lunches in training. Each muscle still rests 2-3 minutes while its opposite number works.
- EMOMs (every minute on the minute). Fixed work on a fixed clock, e.g., 8 reps at the top of every minute for 10 minutes. Progress by adding a rep per round, adding rounds, or shortening the interval. The clock enforces honesty.
- Rest-pause. One hard set, 15-20 seconds of rest, then mini-sets to a rep target. Prestes et al. (2019) found rest-pause training produced comparable strength and, in some measures, greater hypertrophy and endurance versus traditional sets in equal time. Best confined to machines and isolation lifts, where grinding near failure is safe.
- Session benchmarks. The simplest version: log total volume-load (sets x reps x weight) and session length. If the first number rises while the second holds, you are progressing, whatever any individual lift did that day.
The caveat mirrors the rest-period section: density progression counts when loads and reps hold steady or climb while time falls. Compressing a session by letting the weights drift down is rearranging, and on maximal strength work, racing a clock is how technique dies. Keep density methods on hypertrophy and accessory work.
Best for: time-limited lifters, hypertrophy and work-capacity phases, accessory blocks, and home gym training combined with the tempo and ROM methods above.
How to Combine the Methods
Seven levers sounds complicated. In practice you only pull one per lift at a time, and the right one is usually obvious from context.
| Method | What Increases | Best Context | Main Risk |
|---|---|---|---|
| Load | Weight on the bar | Big compounds, strength goals, beginners | Jumps too large; form decay |
| Reps | Reps at fixed weight | Almost everything past the newbie phase | Reps drifting away from failure |
| Sets | Weekly hard sets per muscle | Hypertrophy blocks, lagging muscles | Junk volume, under-recovery |
| Tempo | Work per rep at fixed weight | Equipment limits, rep standardization | Expecting magic from slow reps |
| Range of motion | Distance and stretch per rep | Stretch-responsive muscles, eroded ROM | Untracked ROM changes muddying data |
| Rest | Same output, less recovery | Work capacity, accessories | Cutting rest on heavy compounds |
| Density | Work per unit of time | Time-limited training, hypertrophy | Letting loads drift down to beat the clock |
A sane default structure for a lifter past the beginner stage:
- Main compound lifts: double progression in a 4-8 or 6-10 range, full rest, load added only when the range is maxed. Load and reps do the work.
- Secondary compounds and machines: double progression in 8-12 or 8-15, antagonist pairing to save time. Reps and density do the work.
- Isolation work: wide rep ranges (10-20), tempo standards, lengthened partials past failure when appropriate, shorter rests. Reps, tempo, and ROM do the work.
- Across the block: start near minimum effective volume, add 1-2 weekly sets to priority muscles every week or two, deload after 5-8 weeks. Sets do the work.
When a lift stalls for three or more consecutive sessions despite decent recovery, switch its lever rather than abandoning the lift: a stalled load progression becomes double progression, a maxed double progression gets a new set, a set-saturated muscle gets ROM or tempo work. If you want help assembling these pieces into a full program, our guide to designing your own training program walks through the entire process.
Tracking: The Part Everyone Skips
Every method above shares one dependency: a record. Overload is a comparison between today and last time, and without a log there is no last time. Research on self-monitoring consistently shows that people who track behavior outperform people who estimate it, and lifting is a best-case scenario for tracking because the data is tiny -- exercise, weight, reps, maybe a rest or tempo note.
What makes a log useful for progression specifically:
- Log every working set, including the ugly ones. The failed third set is the most informative data point of the week.
- Fix your standards. Depth, tempo, and rest are part of the measurement. A rep standard that drifts makes the whole log fiction.
- Note reps in reserve. "3 x 8 at RIR 3" and "3 x 8 at RIR 0" are different training sessions that look identical on paper. RIR notation, as popularized in the autoregulation literature by Helms and colleagues, is what lets you see effort trends, anticipate stalls, and know when an added rep was real progress versus borrowed recovery.
- Review monthly, not daily. Day-to-day numbers are noisy -- sleep, stress, and timing swing performance several percent in either direction. The month-over-month trend is the signal. Intermediate lifters progressing on a four-week horizon are doing it right.
App or notebook makes no difference. The habit makes the difference.
Frequently Asked Questions
Is adding weight the only way to progressively overload?
No. Load is one of seven dimensions of training demand. Reps, sets, tempo, range of motion, rest, and density are all measurable, progressable, and supported by research. Plotkin et al. (2022) found that adding reps at a fixed weight built the same muscle as adding weight at fixed reps. The bar weight is the most visible form of progress, but the muscle responds to total demand, however you raise it.
How fast should I expect to add weight to my lifts?
Beginners can often add load weekly for months. Past roughly the first year, expecting weekly jumps on most lifts sets you up to fail and to cheat reps. An intermediate adding 5-10 lb per month on a big barbell lift, or earning a weight increase every few weeks through double progression, is progressing well. Advanced lifters track progress across entire training blocks. The timescale stretching out is normal physiology rather than a personal failing.
Do slow reps build more muscle?
No. Meta-analysis data shows similar growth across rep durations from about 0.5 to 8 seconds, and worse results from super-slow (10+ second) training. Tempo earns its place differently: a standardized controlled eccentric keeps reps honest and comparable, and deliberately slowing a lift can restore progression room when you cannot add weight. Treat tempo as a control and a constraint tool rather than a stimulus multiplier.
Are partial reps useless?
The lockout-style partials people use to fake big numbers are close to useless for growth. Lengthened partials are a different story: reps confined to the stretched portion of the movement have matched or beaten full ROM for hypertrophy in several recent studies, including Pedrosa et al. (2022). Full range of motion remains the sensible default, with lengthened partials as a tool for extending hard sets and for exercises where the stretch is the point.
What should I do when everything plateaus at once?
A simultaneous stall across all lifts points to recovery, not programming. Check sleep first, then calories and protein, then accumulated fatigue -- if you have trained hard for 6-10 weeks without a deload, take one. If recovery checks out and the log says effort is real, then rotate progression levers lift by lift, or change exercise variations for a block to create new room to progress. Single-lift stalls are programming problems; whole-body stalls are recovery problems.
Does progressive overload apply on a cut?
The principle applies; the expectation changes. In a deficit, especially a steep one, maintaining load and reps is the win condition, because preserved performance is the signal that preserves muscle. Beginners and lifters returning from a break can still progress while cutting, and everyone else should fight for maintenance rather than forcing PRs on reduced recovery. Our cutting guide covers how to set the deficit so your training does not collapse.
The Bottom Line
Progressive overload is non-negotiable, but "add weight every session" is just the first chapter of it. The bar weight is one of seven levers, and the research backs the others at full strength: rep progression matches load progression for growth, weekly set counts have a clear dose-response, range of motion and stretch-position training carry their own hypertrophy evidence, and density methods let time-limited lifters keep the demands climbing without a longer session.
The practical playbook fits in a few lines. Run double progression as your default on nearly everything. Add weight when you max the rep range, in jumps sized to the lift. Add weekly sets to priority muscles across a block, then deload. Standardize depth, tempo, and rest so your numbers mean something, and write every set down. When a lift stalls, change its lever before you change your program. When everything stalls, fix your sleep and your food before touching either.
Lifters fail at this principle from two directions: the program-hopper who never applies any progression long enough to work, and the ego-lifter whose loads climb while their range of motion and rep quality quietly pay for it. The fix for both is the same -- pick a lever, measure it honestly, and pull it for months. The bar does not care which dimension got harder. It only cares that something did.
For the surrounding pieces, see our guides on training volume, program design, and sleep -- the inputs that determine whether any progression scheme has a chance to work.
References
- Plotkin, D., Coleman, M., Van Every, D., et al. (2022). Progressive overload without progressing load? The effects of load or repetition progression on muscular adaptations. PeerJ, 10, e14142.
- Schoenfeld, B.J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. Journal of Strength and Conditioning Research, 24(10), 2857-2872.
- Schoenfeld, B.J., Ogborn, D., & Krieger, J.W. (2017). Dose-response relationship between weekly resistance training volume and increases in muscle mass: a systematic review and meta-analysis. Journal of Sports Sciences, 35(11), 1073-1082.
- Schoenfeld, B.J., Ogborn, D.I., & Krieger, J.W. (2015). Effect of repetition duration during resistance training on muscle hypertrophy: a systematic review and meta-analysis. Sports Medicine, 45(4), 577-585.
- Wilk, M., Zajac, A., & Tufano, J.J. (2021). The influence of movement tempo during resistance training on muscular strength and hypertrophy responses: a review. Sports Medicine, 51(8), 1629-1650.
- Schoenfeld, B.J., Pope, Z.K., Benik, F.M., et al. (2016). Longer interset rest periods enhance muscle strength and hypertrophy in resistance-trained men. Journal of Strength and Conditioning Research, 30(7), 1805-1812.
- Schoenfeld, B.J. & Grgic, J. (2020). Effects of range of motion on muscle development during resistance training interventions: a systematic review. SAGE Open Medicine, 8.
- Pallarés, J.G., Hernández-Belmonte, A., Martínez-Cava, A., et al. (2021). Effects of range of motion on resistance training adaptations: a systematic review and meta-analysis. Scandinavian Journal of Medicine & Science in Sports, 31(10), 1866-1881.
- Maeo, S., Huang, M., Wu, Y., et al. (2021). Greater hamstrings muscle hypertrophy but similar damage protection after training at long versus short muscle lengths. Medicine & Science in Sports & Exercise, 53(4), 825-837.
- Pedrosa, G.F., Lima, F.V., Schoenfeld, B.J., et al. (2022). Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. European Journal of Sport Science, 22(8), 1250-1260.
- Prestes, J., Tibana, R.A., de Araujo Sousa, E., et al. (2019). Strength and muscular adaptations after 6 weeks of rest-pause vs. traditional multiple-sets resistance training in trained subjects. Journal of Strength and Conditioning Research, 33(Suppl 1), S113-S121.
- Robbins, D.W., Young, W.B., & Behm, D.G. (2010). The effect of an upper-body agonist-antagonist resistance training protocol on volume load and efficiency. Journal of Strength and Conditioning Research, 24(10), 2632-2640.
- Helms, E.R., Cronin, J., Storey, A., & Zourdos, M.C. (2016). Application of the repetitions in reserve-based rating of perceived exertion scale for resistance training. Strength and Conditioning Journal, 38(4), 42-49.