Optimisation of the efficiency of crushers is desirable in terms of reducing energy consumption, increasing throughput and producing better downstream performance as a result of improved size specification. The mechanism of rock fragmentation within crushers is dominated by compression at high strain rates. Research presented in this paper has investigated the relationship between strain rate, impact energy, the degree of fragmentation and energy efficiencies of fragmentation. For the investigation two laboratory test methods were used to generate compressive failure under different strain rates. The tests were namely a variable speed unconfined compressive strength test, and a laboratory drop weight test. Laboratory testing and computer simulations showed that a greater amount of energy was required for breakage with increasing strain rate and also samples broken at higher strain rates tended to produce a greater degree of fragmentation. It was also observed that not only the impact energy influences the degree of fragmentation but the combination of drop weight/height also has an effect. (c) 2006 Elsevier Ltd. All rights reserved.