Cardio · Machine

Treadmill

A moving belt you walk or run on, with a slope you can raise. It is the most familiar cardio machine in any gym, and the one where two numbers, speed and incline, decide how hard the work is. Get on it slowly, stand tall with your hands free, and let your breathing tell you whether the setting is right.

Measured

Minutes

Loading

None

Ways to use it

Walk, incline walk, run, incline run, walk-run

Counts toward

No muscle's weekly sets

How to do it

1. Start the belt before you step on

   Stand on the side rails, start the belt at its slowest speed, then step onto the moving belt with one foot and then the other. Clip the safety key to your clothing if the machine has one, so the belt stops if you drift off the back.

2. Walk tall in the middle of the belt

   Head up, eyes forward, shoulders relaxed, arms swinging naturally. Stay in the middle of the belt rather than close to the console, where a short stride hits the front of the machine.

3. Build the speed, then the slope

   Raise the speed a little at a time until you reach a pace you could keep up while talking in full sentences. Only then raise the incline, one step at a time. Speed and slope are one dial: raising either makes the work harder.

4. Keep your hands off the rails

   A light touch for balance is fine. If you have to grip the rails to keep up, the setting is too much, so take the speed or the incline down until you can let go.

5. Let your breathing set the effort

   For an easy session you should be able to talk but not sing. On a scale where sitting is 0 and your hardest effort is 10, moderate work sits at 5 or 6¹. If you can only say a few words between breaths, you are working hard.

6. Slow down before you step off

   Lower the incline to flat, slow the belt to a stroll for a minute, then stop it fully and step onto the side rails. Stepping off a moving belt is how people fall.

The five ways

Walk

A flat walk at an easy pace. It is the gentlest way to use the machine, and the place to start. When Reckoner places a walk, it suggests about 4 to 5.5 km/h (2.5 to 3.2 mph), and your breathing has the last word.

Incline walk

The same walk up a slope. Walking up a 10% grade cost about twice the energy of a flat walk in a lab study (113% more), and the hips and calves took on much of the extra work². It is more effort without running, so when Reckoner places a treadmill bout outside a beginner's first week, it is an incline walk, never steeper than 10%.

Run

A run on a flat belt. It is hard work for most people who lift, and runners who are new to running get injured more often than runners who are used to it (see the questions below)⁵.

Incline run

A run up a slope. It is harder again at any speed, and your calves will feel it.

Walk-run

Short runs with walks between. It is the gentle way into running: run for a minute, walk until your breathing settles, and repeat, letting the runs grow over the weeks.

How to start easy

Start flat, at a pace you could talk through, for 5 to 10 minutes. Add a little incline the next time rather than more speed, and give each change a few sessions before the next. "Start low and go slow" is the advice of the US physical activity guidelines for anyone building up¹. When Reckoner places a treadmill bout, it is an easy walk or incline walk and nothing harder. Anything harder is your own choice.

What goes wrong

• Holding on to the rails

  Gripping the console takes weight off your legs, so the numbers say you are climbing a hill that your body is not. If you need the rails to keep up, lower the setting until you do not.

• Treating 12-3-30 as an easy walk

  Twelve per cent incline, 3 mph, thirty minutes is a popular routine, and it is hard work. In a lab study of regularly active adults who were not allowed the rails, one participant could not finish the thirty minutes³. If you try it, treat it as a hard session, not a cool down.

• Cranking the incline before the pace is settled

  A steep slope at a brisk pace is a big jump in effort. Find your easy pace on the flat first, then add slope one step at a time.

• Leaning back on a steep slope

  On a high incline people lean back against their grip on the rails, so their arms are holding them up the hill instead of their legs. Lean slightly into the hill from the ankles, keep your hips under you, and lower the slope if that is not possible.

• Running your longest run on a whim

  The biggest single jumps in distance are when running injuries most often start (see the questions).

Questions people ask

Other machines

Sources

1. Piercy, Troiano, Ballard and colleagues, JAMA, 2018. The Physical Activity Guidelines for Americans the talk test (moderate effort means you can talk but not sing, vigorous means a few words between breaths), the 0 to 10 scale with moderate at 5 or 6 and vigorous from 7 or 8, and "start low and go slow"
2. Silder, Besier and Delp, Journal of Biomechanics, 2012. Predicting the metabolic cost of incline walking from muscle activity and walking mechanics metabolic cost 52% above level walking at a 5% incline and 113% above at 10%, at each subject's preferred speed; peak hip extension moment and hip power generation rose with incline, and the activity of every measured muscle but the shin muscle rose with it
3. Wong, Davis, Perez and colleagues, International Journal of Exercise Science, 2025. An exploratory study comparing the metabolic responses between the 12-3-30 treadmill workout and self-paced treadmill running regularly active adults, handrails not allowed, one participant could not complete the 12-3-30 session
4. Sato, Krieger, Gidley and colleagues, International Journal of Exercise Science, 2024. Physiological and psychological differences between 20% grade incline walking and level-grade jogging at isocaloric intensity in inactive young adults, oxygen uptake during a 20% incline walk matched level jogging, with higher enjoyment for the jog
5. Videbæk, Bueno, Nielsen and colleagues, Sports Medicine, 2015. Incidence of running-related injuries per 1000 h of running in different types of runners: a systematic review and meta-analysis 17.8 injuries per 1000 hours in novice runners against 7.7 in recreational runners
6. Frandsen, Hulme, Parner and colleagues, British Journal of Sports Medicine, 2025. How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study a single session more than 10% longer than the longest run of the prior 30 days raised the rate of overuse injury (hazard rate ratio 1.64 for a 10 to 30% spike), measured with Garmin devices