Same six reps. Four different sessions.

The rep count tells you almost nothing about what the set actually did.

Two lifters do a dumbbell row. Same weight, same ten reps. One takes forty-five seconds over it. The other rips through in eight and drops the bells on the floor. I have watched that comparison play out for thirty-five years and it never stops being the same lesson.

Everything else on the sheet gets argued about. Exercise selection, sets, rest, percentages. Then the one parameter that decides what happens inside the set gets left blank, and the lifter fills it in with whatever rhythm he happens to prefer.

This piece is about filling it in on purpose. By the end you should be able to take one exercise and one rep bracket and aim it at four genuinely different qualities — and know when doing so will help an athlete and when it will quietly cost him. It is written mainly for young coaches, and for the lifter who leaves the gym unsure what the session was for.

The four numbers

• First digit — the eccentric. Lowering. The muscle lengthening under load.
• Second digit — the pause in the stretched position. Bar on the chest. Bottom of the squat. Poor leverage.
• Third digit — the concentric. Lifting. An X means accelerate as hard as you can.
• Fourth digit — the pause in the shortened position. Locked out. Top of the curl. Good leverage.

A bench press at 4210 is four seconds down, two paused on the chest, one second up, straight into the next rep.

Two traps catch nearly everyone in the first month.

The digits are ordered by contraction type, not by what happens first in the exercise. On a lat pulldown the concentric comes first, but it is still the third digit. A pulldown written 3010 means one second to pull and three to return. Write it in movement order and you will get it backwards, and so will everyone you coach.

And X does not mean the bar moves fast. It means you are trying to make it move fast.

Under a heavy load the bar will crawl, and that is fine — the nervous system responds to the attempt, not to the stopwatch. This is well established and it is the single most useful item on the list, because it means you can train explosive intent with heavy weight.

Once you have a tempo, you have a clock.

Time under tension decides which fuel system runs the set, and that decides a great deal about what adapts.

The working rule I use: relative strength lives under twenty seconds, forty at the outside. Hypertrophy lives between forty and seventy. For athletes in strength sports that also demand speed, stay under forty — in my experience the size built by longer sets does not travel well onto the field.

Now take six reps and change nothing but the tempo.

Eighteen seconds to sixty. Same exercise, same six reps, same sheet. Four sessions.

Six is arbitrary here — I picked it because it holds the arithmetic still. Run the same exercise at four reps or at ten and the whole table moves. What matters is the relationship, not these four rows.

The two pause positions do opposite jobs. Pausing in the stretched position raises tension by dissipating the elastic energy you would otherwise get for free — the muscle has to work harder for the same weight. Pausing in the shortened position does the reverse: a rest in the strong position lets you handle more load and biases recruitment towards high-threshold motor units. So 44X1 for size. 40X3 for force. Same bench press, opposite intent.

The tempo map

Reps and tempo together give you a time under tension, the time under tension tells you which system is running the set, and that tells you what you are actually going to get.

Read it downwards and you can see the trade in plain sight. As you descend, the load falls, the size goes up, and the transfer to anything explosive goes down. Nothing in that table is better than anything else. They are five different purchases.

And treat the numbers as a starting point rather than a rulebook. The tempos in that table are the ones I reach for most, not the only ones that work, and the rep figures assume an average athlete who does not exist. Use it to understand the relationships — reps, tempo, time, system, outcome — and then move the numbers to fit the person in front of you.

Two limits on the map, both worth knowing before you lean on it.

It does not show rest. Two sets with identical time under tension and different rest intervals are not the same training session — the same forty seconds with three minutes' rest and with forty-five seconds' rest produce genuinely different hormonal and metabolic outcomes. Tempo and rest interact, and you can use one to compensate for the other. That is an article of its own and I will write it.

And there is not a single percentage of 1RM in it, deliberately. There is no reliable way to attach a percentage to a tempo-prescribed set. What eighty percent means for six reps depends on the muscle, the exercise, the athlete's fibre makeup and his training age, and it moves as he gets stronger. Sometimes the load matters more than the tempo, and sometimes what actually needs measuring is an output — bar speed, jump height, how he moves the next morning — rather than either one. That is a third article, and honestly it may be the more important one.

What a slow concentric actually costs you

This is the part almost nobody thinks through, and it decides where tempo work belongs in a year.

The eccentric is metabolically cheap. Producing force while lengthening costs several times less oxygen and ATP than producing the same force while shortening — the tissue is being paid to resist rather than to move. That is why you can lower far more than you can lift. But cheap in fuel does not mean cheap: the eccentric bills you in a different currency, which is muscle damage and recovery days. A long eccentric buys tension and adaptation without much metabolic cost and hands you soreness instead.

The concentric is where the fuel goes, and speed changes the bill completely.

A fast concentric is expensive in nervous system and cheap in fuel. Force is mass times acceleration, so trying to accelerate hard means high force whatever the bar actually does. Set durations stay short, so the work runs largely on stored phosphagens. Little glycogen depletion, few metabolites, and recovery between sets is quick — which is why heavy explosive work asks for three to five minutes of rest and genuinely gives it back to you. You are buying recruitment and rate of force development.

A slow concentric is expensive in fuel and cheap in force. Move slowly against a submaximal load and you have deliberately capped acceleration, so force per rep is lower. But the rep lasts three or four times longer, so energy turnover per set climbs steeply and you drop into glycolysis. Tension stays continuous, restricting blood flow, trapping metabolites and driving pH down. You are buying metabolic stress, connective tissue time and control of the movement. You are not buying peak force, and you are spending glycogen to get it.

Neither is better. They are different purchases with different price tags. But notice what that means for an athlete: a session built on slow concentrics leaves him flat, sore and depleted, competing directly with his conditioning and his skill work. A session built on X concentrics leaves him neurally tired with his fuel intact.

That single difference is why tempo is not only a set-level decision. It is a calendar decision.

The muscle has a job.

Here is the mistake I see most often in young coaches. They pick a tempo for the goal and forget to check it against the muscle.

Muscles are not interchangeable tissue. Their fibre makeup usually reflects what they do for a living. The hamstrings as knee flexors and the gastrocnemius are fast-twitch dominant — they exist to produce enormous force in a fraction of a second. The soleus underneath is the opposite, reported anywhere between seventy and ninety percent slow-twitch depending on which autopsy series you read, because its job is to hold you up all day. The adductors lean slow-twitch. The quadriceps tolerate, and frequently need, far more reps and far longer sets than most people give them.

That has two consequences.

Prescribe below a muscle's needs and you never stimulate it. Put a soleus through six explosive reps and you have done nothing to it. That muscle needs fifteen to twenty-five reps and real time under tension before anything happens. You will produce an athlete with a strong-looking lower leg whose ankle stops holding up in the last fifteen minutes.

Prescribe against a muscle's function and you can make transfer worse. Deliberately slow lifting shifts the force-time curve to the right: more force, produced later. For a muscle whose entire sporting job happens inside a tenth of a second — a knee flexor in sprinting, a calf at takeoff — later is not neutral. It is the wrong direction. Grind a hamstring curl on a four-second concentric for eight weeks and you get a stronger hamstring on the machine and an athlete who is no faster, sometimes slower off the mark. He got strong in a mode he never uses.

Ask what the muscle does, then what the block needs, then what tempo. Not the other way round.

In practice that means fast-twitch dominant, explosive-role muscles get short sets, low reps and X concentrics almost year-round — though I will still use a long eccentric on them, because sprinting loads a hamstring eccentrically anyway and that is a quality worth owning. Postural and stabilising muscles get longer tempos and much higher reps, and I stop worrying about whether it looks explosive.

Two honest caveats. Individual fibre makeup varies, sometimes wildly, and you cannot know it without a biopsy nobody is going to have. The field proxies — reps managed at eighty percent of max, or how deep and slow the dip is before a vertical jump — are rough, and I treat them as a hint.

And be clear about which part of this is evidence and which part is me. That muscles differ in fibre makeup, and that different muscles have responded differently to the same tempo in the few studies that split it out — that much is supported. The specific rules I have just given you are not. Nobody has trained one group of athletes' hamstrings slowly, another group's quickly, and measured what happened to their sprint. The transfer argument is a mechanism that makes sense to me plus thirty-five years of watching, and that is a coach's judgement, not a finding.

And the exercise has a shape.

The second thing to check is the exercise itself — specifically its strength curve, meaning how the resistance lines up against your leverage through the range.

Slow tempo work only makes sense where the exercise can carry it. If the load falls away at one end of the movement, a long eccentric spends part of its time in a zone where almost nothing is happening, and you have bought seconds instead of tension. If there is a pronounced sticking point, the weight you can use is capped by that one angle, so the rest of the range is under-loaded no matter how carefully you count. Either pick an exercise whose resistance profile matches the muscle, accommodate it with chains or bands, or put the pause exactly at the angle that is limiting you and stop pretending the rest of the range is being trained.

Range of motion matters here too. The longer the range, the longer the eccentric needs to be, purely for control — a squat on a ten-second eccentric carries risk a reverse wrist curl does not, because there is more distance in which to lose the bar path. And some movements barely give you room to play at all. Calves have a short range, which is why calf programming has to lean harder on reps, sets and rest intervals instead. Recognising which exercises are tempo-poor saves you writing prescriptions that cannot be executed.

Then there is the category where most of this stops applying entirely.

Never put a slow eccentric or a slow concentric on a classic lift.

A snatch, a clean, a jerk, a power version of any of them — those are X on both. The concentric is the exercise: the whole point is maximum rate of force development, and a one-second pull is a failed lift, not a slow one. And there is no eccentric worth prescribing, because you are catching kilos or returning them, not lowering them under control. Writing 3010 next to a power clean tells me you have not understood what the movement is for. A useful weightlifting tempo looks like XOXO, and mostly you leave it alone.

What you can play with is the other two digits. The pauses are where the coaching lives in these lifts, and they are genuinely powerful:

• A pause above the knee on a clean pull, for the athlete who rushes the first pull and arrives at the hip with nothing left to give.
• A pause in the receiving position, to build the confidence and the positional strength to stay under the bar.
• A pause at whichever point in the pull the athlete keeps skipping past.

Note that this is the second digit doing a job it is not usually described as doing — a pause part-way through the concentric, at a chosen joint angle, rather than in the stretched position at the bottom. Same digit, and one of the more useful things you can do with it.

And if you want slow work inside a weightlifting programme, you use the derivatives, not the competition lift. A snatch deadlift from a podium on a five-second eccentric is excellent. A slow snatch is not a thing.

Where this goes wrong in practice.

Counting instead of lifting. If attention is on the clock rather than the load, tempo has cost more than it bought. Teach it in the warm-up sets, then let rhythm carry the working sets. A tempo you have to think about is a tempo you have not learned yet.

Using tempo instead of load. Slowing everything down feels productive and produces a hard session with no progression underneath it. Tempo changes the direction of the stimulus. It does not replace adding weight over time.

Leaving the column blank. I write a tempo on every programme, and this is why. Left to himself, every lifter drifts back to the rhythm he is already good at. Nothing wrong with that rhythm — it is usually why he has whatever he has. But the qualities he lacks are almost always sitting at the tempos he never uses. The prescription exists to make the unfamiliar happen on purpose. Where I give ground is on the day: when the session is about expressing strength rather than building a quality, I get more forgiving about the last two reps.

Pick one lift this week. Write four digits next to it. Count them out loud on the first set.

• The rep bracket is fixed. Tempo picks the load. Fail inside the bracket. If the tempo breaks early the weight was too heavy; if it survives past the top the weight was too light.
• When the tempo breaks, the set is over. Failure is the moment the weight stops moving the way you asked for, not the moment it stops moving.
• Under 20 seconds per set — strength and neural quality. Low reps, generous rest.
• 20–40 seconds — the athlete's zone. Size that still moves.
• 40–70 seconds — hypertrophy.
• Down slow, up fast is the default. Three to five seconds on the eccentric; slower than that and you reach the concentric already tired.
• X is intent, not speed. Try to throw it. The bar will do what it does.
• Slow concentrics cost glycogen and buy control. Fast concentrics cost nervous system and buy force. Spend accordingly.
• Stretched pause raises tension for the same load. Shortened pause lets you use more load.
• Ask what the muscle does before you ask what the block needs. Explosive muscles, short sets. Postural muscles, long ones.
• Check the strength curve before you slow anything down. No point counting seconds through a range where the load has fallen off.
• Classic lifts are X on both. Coach them through the pauses, and put your slow work in the derivatives.
• Long range, long eccentric. Short range, less room to play.
• Ride a wave, do not run blocks. Change what leads, keep everything else on the sheet in a small dose. A quality that took eight weeks to buy can often be held with one set.
• Slow to fast across the year. The direction holds for everyone. The specifics — full range, partials, isometrics — are person dependent. Change the leading tempo when the wave turns.
• No percentage survives a tempo change. Eighty percent for six reps means nothing until somebody says at what speed.

The first lifter finished his ten reps in eight seconds. Give him the same ten at 4210 and he will find out, somewhere around rep four, exactly what he has been avoiding.