Log or Water Carry
A fairly low-level obstacle course can become a punishing circuit if competitors carry a heavy log around the course. The competitor must maintain bodily contact with the log at all times and must not allow it to touch the ground at any point. This will not only increase the workload on the legs but also makes balancing and climbing tasks far harder in terms of physical strength and technique. Alternatively, have them carry a yoke with water buckets at each end make them redo any circuits in which they spill too much water. Ensure that the obstacles you use are not impossible without the free use of the arms.
Hang Tough Course
You can create a real test of endurance by setting a course in which the the competitors are constantly suspended by their arms with few or no opportunities for rest. Use wide spanned and ascending monkey bars, rope climbs and overhanging ladders to test the arms, shoulders, back and core strength. Set up an additional challenge by having competitors carry a backpack weighted proportionally to their body weight.
Float Through Hoops Course
Standard courses challenge the lifting and carrying muscles of the back, legs and triceps more than the pressing muscles of the biceps and chest. Set a course which bucks this trend by positioning a series of hoops in a swimming pool or lake. Position the floating hoops vertically and tie them to anchors so that they float a few feet beneath the surface of the water. Challenge competitors to push a large, inflatable ball down and through each of the hoops in turn. Having to force and control the ball against its natural buoyancy can take real strength. Increasing depth and demanding they complete a sequence of hops before the ball can surface also presses competitors against the psychological barrier of holding breath. However, safety must always be paramount in laying out and conducting the course.
Test the fortitude of participants by elevating a standard obstacle course to an intimidating height. This will of course take a certain amount of planning and mandate the highest standards of safety with regards to harnessing or safety nets. However, the presence of a significant drop can turn simple balances into challenging obstacles. To give their resolve a real push, have them carry the yoke and water buckets as described in Section 1.