How can I effectively manage the physical strain and maintain control without the ability to shift gears?

Climbing steep trails on a fixed gear mountain bike can indeed be challenging. Without gears to shift, you're reliant entirely on your leg strength and momentum. To manage this, focus on maintaining a steady, consistent pace and try to anticipate changes in the terrain to adjust your speed accordingly.

Stand up on the pedals to leverage your body weight when the climb becomes particularly tough. Also, ensure your bike's gear ratio is suitable for the types of trails you ride; sometimes, a slight adjustment can make a significant difference. Building leg strength through specific exercises off the bike can also help. Lastly, practice makes perfect over time, you'll develop the necessary skills and endurance to handle these climbs more efficiently.