Conversely , all humans have red slow - twitch fibers that ca n't produce much force .
Humans are highly resistant to fatigue and allow us to run marathons or hike for eight - 12 hours at a time .
Conversely , all humans have red slow - twitch fibers that ca n't produce much force , yet they are highly resistant to fatigue and allow us to run marathons or hike for eight - 12 hours at a time .