Effects of slope, substrate, and temperature on forces associated with locomotion of the ornate box turtle, Terrapene ornata

In spite of several studies of the locomotor performances of reptiles, we know as yet relatively little about the mechanical forces involved. The present investigation examined the effects of substrate, slope and temperature on the pulling forces exerted by ornate box turtles tethered to a force transducer. These forces increased with body mass in a nearly isometric manner. The forces exerted during the initial effort were greatest on a styrofoam substrate, whereas maximum forces generated were greatest on pea gravel. Both forces progressively increased as slope decreased from +30 degrees to -30 degrees. The rate of force generation (N/s) was greatest at intermediate slopes. Contact force tended to increase as normal force increased, and was strongly influenced by slope, increasing from -30 degrees to +30 degrees. Surprisingly, we found no significant effects of temperature on tether forces, contraction times, or rates. This evaluation of pulling forces associated with box turtle locomotion revealed some interesting, and at times unexpected, relationships.