A strongman is an athlete who performs feats of seemingly superhuman strength. They deadlift cars, move giant boulders and flip huge truck tires that would normally take two or three men to move. Strongmen develop this god-like strength by lifting immensely heavy weights at the gym. But, what if you're someone who doesn't like lifting weights? Could you achieve strongman-strength though nothing but bodyweight training? Unfortunately, no. However, you could still get strongman-strength by only doing bodyweight exercises with added resistance.
To be a strongman you have to be able to bench far more than your own bodyweight. Doing normal pushups won't give you this kind of strength. However, if you fill a backpack with weights (stones, sand, weight plates, water bottles), you can increase the resistance beyond your own bodyweight and turn a normal pushup into a more challenging exercise. You can also simply put a weight plate on your back or have someone sit on your back. Just make sure you keep the weight position up toward your shoulders to prevent lower back injury.
Pullups are an excellent compound exercise for developing upper-body strength. Average men struggle to do just one pullup, so if you can manage to a few or more, you are already stronger than most. However, a strongman can pull several times his own bodyweight for long distances. The concept behind doing backpack pullups is the same as backpack pushups. Fill a backpack up with weights, strap it around your shoulders and start doing pullups.
Strongmen deadlift cars and carry hundreds, sometimes thousands of pounds, on their shoulders. You need thighs like tree trunks to perform these feats of strength. Once again, the same concept as backpack pullups and pushups applies. Fill a backpack with heavy weights and then do squats. This exercise will help you develop powerful quads and glutes. Some gyms have tires of various sizes with which to train. Another training device is a weight sled. Varying amounts of weights are added to the sled and you then push or pull the sled.
Isometric exercises are exercises in which you hold the resistance in one position for a certain amount of time. So, rather than lifting an object or going through a range of motion, you simply hold the weight in one position for as long as you can. (You don't move any joints.) For bodyweight, a plank is an example. Gymnasts use isometrics as a part of their regular conditioning. You perform isometrics in a variety of ways: holding yourself in a pushup position, hanging from a pullup bar, holding a squat, etc... Again, you can make the exercises more challenging by wearing a weighted backpack or weight vest.
Strongman are able lift huge boulders and flip giant tires, some of which weigh up to 750 lbs. This takes a lot of explosive, plyometric strength. One way you can activate your muscle fibers in a similar fashion without using any weights is by pushing against immovable objects. This is another type of isometric exercise. For example, stand in front of a tree or a wall and try to push it over with all your might. Your brain will know this is impossible but your muscles won't and they'll respond accordingly. If you push your house over in the process, skip the competition and become a super-hero.