Muscular Strength Training Effects on Aerobic Endurance Performance, a Review

Pate and Kriska (1984) have described a model that incorporates the three major factors that account for interindividual variance in aerobic endurance performance, namely maximal oxygen uptake (VO2max), anaerobic or lactate threshold (LT) and work economy (C). Numerous published studies support the model and thus, the model should serve as a useful framework for the comprehensive study of strength training effects on aerobic endurance performance. VO2max is probably the single most important factor determining success in an extreme aerobic endurance sport. In order to obtain relevant values emphasize is placed on testing in sport specific activities. The best-level male international cyclists, as the best middle and long distance runners, have a maximum oxygen uptake of more than 85 ml kg min (Helgerud et al. 1990). It has been well documented that also mithochondrial density, oxydative enzyme activity and capillary density increase with endurance training. At maximal exercise, the majority of evidence points to a VO2max that is limited by O2 availability (Richardson 2000), again limited by cardiac output and thus the stroke volume of the heart. The stroke volume of the heart can be twice as high in a trained athlete compared to a sedentary person. Although researchers agree that stroke volume increases as work rates increase up to around 50% of VO2max , reports about what happens after that point differ widely. A study by Zhou et al. (2001) found that stroke volume increased continuously with increased workload up to VO2max in well-trained subjects. However, in sedentary and moderately trained subjects the classical levelling off was found. The increased stroke volume up to the level of VO2max in trained athletes has been the rationale behind using high intensity aerobic training intervention in our endurance training. An endurance athlete is able to maintain repetitive bouts at this intensity level for 3 to 8 minutes. There is no literature proposing that strength training might improve VO2max. LT determines the fraction of the maximal aerobic power that may be sustained for an extended period of time. The blood lactate level represents a balance between lactate production and removal, and there are individual patterns in this kinetics. Lactate is not wasted and can either be oxidized or to a smaller extent be a substrate for synthesis of glucose and glycogen. When oxidized it yields the remaining 92 % of energy and both resting and submaximally working skeletal muscle, as well as heart muscle and kidney cortex can use lactate as a substrate. Values as high as 90% of maximal oxygen uptake have been observed in some highly proficient endurance athletes. LT changes with the alteration of VO2max, but in terms of % of VO2max the trainability seems to be minor. No literature is proposing that strength might improve LT in % of VO2max. Work efficiency is referred to as the ratio between work output and oxygen cost. Running economy (CR) is commonly defined as the steady state VO2 in ml ⋅ kg⋅ m at a standard velocity or as energy cost of running per meter (mlkgm). Several authors have shown intra-individual variations in gross oxygen cost of activity at a standard running velocity (Helgerud 1994). The causes of this variability are not well understood, but it seems likely that anatomical trait, mechanical skill, neuromuscular skill and storage of elastic energy are important. Work economy or work efficiency is the element within the endurance performance that seems to be able to change with certain strength parameters.