IMPACT OF RESISTANCE TRAINING ON ENDURANCE PERFORMANCE - A NEW FORM OF CROSS-TRAINING

In accordance with the principles of training specificity, resistance and endurance training induce distinct muscular adaptations. Endurance training, for example, decreases the activity of the glycolytic enzym es, but increases intramuscular substrate stores, oxidative enzyme act ivities, and capillary, as well as mitochondrial, density. In contrast , resistance or strength training reduces mitochondrial density, while marginally impacting capillary density, metabolic enzyme activities a nd intramuscular substrate stores (except muscle glycogen). The traini ng modalities do induce one common muscular adaptation: they transform type nb myofibres into IIa myofibres. This transformation is coupled with opposite changes in fibre size (resistance training increases, an d endurance training decreases, fibre size), and, in general, myofibre contractile properties. As a result of these distinct muscular adapta tions, endurance training facilitates aerobic processes, whereas resis tance training increases muscular strength and anaerobic power. Exerci se performance data do not fit this paradigm, however, as they indicat e that resistance training or the addition of resistance training to a n ongoing endurance exercise regimen, including running or cycling, in creases both short and long term endurance capacity in sedentary and t rained individuals. Resistance training also appears to improve lactat e threshold in untrained individuals during cycling. These improvement s may be linked to the capacity of resistance training to alter myofib re size and contractile properties, adaptations that may increase musc ular force production. In contrast to running and cycling, traditional dry land resistance training or combined swim and resistance training does not appear to enhance swimming performance in untrained individu als or competitive swimmers, despite substantially increasing upper bo dy strength. Combined swim and swim-specific 'in-water' resistance tra ining programmes, however, increase a competitive swimmer's velocity o ver distances up to 200m. Traditional resistance training may be a val uable adjunct to the exercise programmes followed by endurance runners or cyclists, but not swimmers; these latter athletes need more specif ic forms of resistance training to realise performance improvement.