Swimming is a sport that presents significant opportunities to apply information gained from physiological testing (Prins 1988, Treffene 1979, Troup 1984 and 1986). There are a number of benefits that can be obtained from a well-planned testing program (refer to chapter 17 Protocols for the Physiological Assessment of High Performance Track, Road and Mountain Cyclists). Within Australia, the testing protocols outlined in this section have been approved by the Sport Sciences Advisory Group of Australian Swimming Inc (ASI). The national body (ASI) is administering these tests to Australian swimmers through its National Team and National Event Camp Program and in High Performance Centres linked to state institutes or academies of sport. While some national level swimmers have a formal requirement to undertake these tests, it is not the intention to stifle the creativity of scientists and coaches in developing and utilising their own swimming testing protocols. The tests outlined in this section are largely pool-based for reasons of specificity and practicality. Few nations possess a purpose-built swimming flume necessary for routine measurement of oxygen uptake during swimming. Although it is possible to measure oxygen uptake during swimming in a conventional pool, or to estimate it using techniques such as backward extrapolation, the practical difficulties associated with these approaches have limited their use in testing large numbers of swimmers. A large number of different testing protocols have been described in scientific and coaching literature to assess various components of fitness in highly trained swimmers (Roberts 1991). While these tests only provide an indirect estimation of the contribution of different energy systems, they do not have the limitations inherent in laboratory tests of running, cycling and rowing where results must be transferred to the field. The underlying rationale for the tests described here is this: physiological information derived from a swimmer during submaximal and maximal testing provides critical detail for the coach to determine training loads and monitor performance improvements (Roberts 1991).