Background: Extensive literature has described a decrease in force output performance in the local muscle groups after static stretching, and static stretching has therefore been recommended not to be performed during warm-ups. A recent study showed evidence of a cross-over effect in regard to static stretching, i.e. non-local muscles were also affected by static stretching. This result could however be due to fatigue in the muscle groups stretched, and a fatigued condition has previously shown cross-over effects in several studies. Aim: The aim of the study was to (1) examine if upper-limb static stretching and muscle fatigue display a cross-over effect that show changes in force output in the lower limbs, and (2) if there was a difference between the effects of the static stretch protocol and the muscle fatigue protocol for the purpose of examining if fatigue is the larger factor for cross-over. Methods: Concentric maximal jump height of 15 subjects with previous strength training experience of at least one year was measured and the subjects subsequently performed both intervention protocols in a random order. After each protocol concentric jump height was measured again. The static stretch protocol consisted of a static stretch for the shoulder at an intensity of “Very hard”, 10 repetitions of 30 second stretches with 15 seconds rest in between repetitions. The muscle fatigue protocol consisted of 10 repetitions of 30 seconds isometric muscle contraction in the same position with 15 seconds rest between repetitions at an intensity of “Very hard”. The data was collected on an infra-red contact mat and differences between the mean jump heights pre- and post each protocol and between the different protocols were analyzed with pair sample t-test.   Result: Mean concentric jump height (± standard deviation, SD) was 25.31 (±9.4) cm for the baseline jumps, 23.66 (±8.89) cm post static stretch intervention jumps and 24.13 (±8.90) cm post muscle fatigue intervention jumps. This indicates a cross-over effect on force output in the legs post static stretching with a mean reduction of 1.65 cm (p=0.001). Upper-limb muscle fatigue indicated a cross-over effect on force output in the legs with a mean reduction of 1.18 cm (p=0.032). There was no statistical significance between the two protocols (p=0.146). Conclusion: The results presented a cross-over effect on both conditions. This is in line with previous research in the area. The results implicate that static stretching and muscle fatigue effects the central nervous system, which can lead to impairments in performance in non-local muscles. This can be considered in warm-up and exercise program design when force output is of great importance for performance