I am sure all athletes have experienced the effects of muscle fatigue. You will use your body differently, trying to compensate by moving your limbs in a more comfortable way. Try going down stairs right after a marathon and you get the picture.
An interesting question is, do everyone compensate using the same strategy? Apparently not. A recent study¹ shows people with recurrent low back pain jogs with a different compensation strategy compared to healthy individuals after a set of fatiguing lower back muscle endurance exercise. The exercise was to hold the lower back in an extended position until their muscles shows signs of fatigue on surface electromyography (EMG). The low back pain group was found to jog with a more extended or arched lower back and had more hip movements whereas the normal healthy group runs with a more forward flexed trunk. This may be why it is a common for people with chronic low back pain to complain of hip muscle soreness and fatigue after endurance exercises. It is a known fact that chronic low back pain sufferers have poor core muscle function. This adaptation of running with an extended back may be a strategy to stabilise the lower back without the need to use core muscles and yet able to continue running. On the other hand, healthy individuals are able to use their core muscles as a natural trunk stabiliser and prevent unnecessary movements. Parallels can be drawn with long hours of sitting where the body requires muscle endurance to sustain in a single position. When fatigue sets in, the body may adopt a different strategy to try to protect the back and inadvertently creates a wrong movement pattern or mal-adaptation. Therefore, correcting wrong movement patterns and strengthening of the core muscles are important aspects of treating chonic low back pain. Reference: 1. Hart JM, Kerrigan DC, Fritz JM, Ingersoll CD. Jogging Kinematics After Lumbar Paraspinal Muscle Fatigue Journal of Athletic Training. 2009; 44(5):475–481 Picture: www.amercianrunning.org