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David White

I'm a long-time reader and occasional donor to Low Tech Magazine and was excited to read that you are doing a project in Utrecht because I live nearby in Baarn. Will there be a public exhibition of the system?

Besides that, some comments about the power generation. One of my hobbies is strength training and the estimates of wattage possible from different exercise machines at http://www.humanpowerplant.be/2017/05/power-potential-various-exercise-machines.html struck me as unusual, especially the idea that a lat pulldown machine would have a higher power output than lower body exercises like a leg press. A number of observations:

1. Are you sure the calculations are correct? The article says that each weight was lifted around 15 times in a minute and the watt values for the lat pull are ~600W. Because 1 kg-m/minute is 0.16W (http://www.convertunits.com/from/kg-m/min/to/watt), and the travel for the weight on a lat pull is around 1 meter, that would seem to imply that you were using a weight of 250kg:

250 kg x 1 meter x 15 reps in a minute = 3600 kg-m in a minute = 600W

I could believe 80kg x 15 reps in a minute = 192W, but 600W on a lat pulldown sounds wild.

As a different way of seeing that the 600W sounds too high, consider that the world records for using a rowing machine on a 500m distance (http://www.concept2.com/indoor-rowers/racing/records/world?machine=1&event=500&gender=Male&age=All&weight=All) are 1m10s - 1m20s depending on weight/age, and a 1m20s pace is 683W (http://www.concept2.com/indoor-rowers/training/calculators/watts-calculator). So the odds of an untrained subject producing 600W for a period of one minute on an apparatus not optimized for demonstrating power output (i.e., it is easier to generate power on a rower than the lat pulldown) are basically zero.

2. I suspect that there are some measurement artifacts in your data, e.g.:

- Max power production is very sensitive to the load used, and 30-40% of the maximum you can lift usually produces the highest power output. Was the load too heavy for the leg press machine?
- Was there some friction on the leg press machine that was not present on the pull-down machine and not measured in the output of the leg press machine?
- Was your technique different? For example, did you lower the weight slowly on the leg press to avoid banging the plates together, whereas the long vertical distance on the lat pull down enabled you to let that weight free-fall for a bit?

With the right equipment, it should be easy for a lower-body exercise to beat an upper body exercise. Some exercises that should produce much more power than a lat pull down would include:
- Deadlift variations
- Squat variations
- If a clever apparatus could be built for this purpose, something that involves pulling or pushing an object across a distance. The mechanics would mimic https://www.youtube.com/watch?v=C9nw2JY30JI (person is leaned over driving forward with the legs) but the person might be wearing a harness or hip belt attached to a long strap driving a ratchet mechanism rather than pushing a sled.

3. Strength is a very trainable quality, and most beginners can double their strength in a 3-month period. Gains in power won't be quite as dramatic, but there should be at least +50% gains possible in power generation from untrained subjects after a month of training every day.

If it would be productive I would be happy to come to the site some time to play with the equipment and talk about how you could design exercises to maximize power output.

Regards,
David

David White

Some comments about the power generation. One of my hobbies is strength training and the estimates of wattage possible from different exercise machines at http://www.humanpowerplant.be/2017/05/power-potential-various-exercise-machines.html struck me as unusual, especially the idea that a lat pulldown machine would have a higher power output than lower body exercises like a leg press. A number of observations:

1. Are you sure the calculations are correct? The article says that each weight was lifted around 15 times in a minute and the watt values for the lat pull are ~600W. Because 1 kg-m/minute is 0.16W (http://www.convertunits.com/from/kg-m/min/to/watt), and the travel for the weight on a lat pull is around 1 meter, that would seem to imply that you were using a weight of 250kg:

250 kg x 1 meter x 15 reps in a minute = 3600 kg-m in a minute = 600W

I could believe 80kg x 15 reps in a minute = 192W, but 600W on a lat pulldown sounds wild.

As a different way of seeing that the 600W sounds too high, consider that the world records for using a rowing machine on a 500m distance (http://www.concept2.com/indoor-rowers/racing/records/world?machine=1&event=500&gender=Male&age=All&weight=All) are 1m10s - 1m20s depending on weight/age, and a 1m20s pace is 683W (http://www.concept2.com/indoor-rowers/training/calculators/watts-calculator). So the odds of an untrained subject producing 600W for a period of one minute on an apparatus not optimized for demonstrating power output (i.e., it is easier to generate power on a rower than the lat pulldown) are basically zero.

2. I suspect that there are some measurement artifacts in your data, e.g.:

- Max power production is very sensitive to the load used, and 30-40% of the maximum you can lift usually produces the highest power output. Was the load too heavy for the leg press machine?
- Was there some friction on the leg press machine that was not present on the pull-down machine and not measured in the output of the leg press machine?
- Was your technique different? For example, did you lower the weight slowly on the leg press to avoid banging the plates together, whereas the long vertical distance on the lat pull down enabled you to let that weight free-fall for a bit?

With the right equipment, it should be easy for a lower-body exercise to beat an upper body exercise. Some exercises that should produce much more power than a lat pull down would include:
- Deadlift variations
- Squat variations
- If a clever apparatus could be built for this purpose, something that involves pulling or pushing an object across a distance. The mechanics would mimic https://www.youtube.com/watch?v=C9nw2JY30JI (person is leaned over driving forward with the legs) but the person might be wearing a harness or hip belt attached to a long strap driving a ratchet mechanism rather than pushing a sled.

3. Strength is a very trainable quality, and most beginners can double their strength in a 3-month period. Gains in power won't be quite as dramatic, but there should be at least +50% gains possible in power generation from untrained subjects after a month of training every day.

If it would be productive I would be happy to come to the site some time to play with the equipment and talk about how you could design exercises to maximize power output.

Regards,
David

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