Build strength by "climbing" up and down in intensity.
Contract at 20% intensity, hold 5 seconds
Increase to 40% intensity, hold 5 seconds
Increase to 60% intensity, hold 5 seconds
Increase to 80% intensity, hold 5 seconds
Maximum 100% intensity, hold 5 seconds
Drop back to 80%, hold 5 seconds
Continue descending: 60%, 40%, 20%
Rest 30 seconds, repeat 3 times