Performance in most endurance events is determined by the maximal sustained power production for a given competition distance, and the energy cost of maintaining a given competition speed. In shorter endurance events and during accelerations and sprint situations, anaerobic capacity and maximal speed may also contribute to performance. Strength training could thus contribute to enhance endurance performance by improving the economy of movement, delaying fatigue, improving anaerobic capacity and enhancing maximal speed (Ronnestad & Mujika 2014). The above improvements are observed as a result of high-intensity strength and plyometric training in various endurance sports including male and female cross-country skiing, cycling, running, and triathlon (Millet et al. 2002). In most cases, strength training had no significant effect on determinants of endurance performance such as maximal oxygen uptake (V02max), and the gains in movement economy are often attributed to mechanisms residing within the skeletal muscles, such as increased lower leg musculontendinous stiffness and/or improvements in running mechanics (Saunders et al. 2006). Replacing a portion of endurance training with explosive strength training can contribute to performance of trained cyclists and runners. In terms of neuromuscular and anaerobic characteristics, concurrent explosive strength and endurance training can result in improved maximal anaerobic speed, and selective neuromuscular performance characteristics including concentric and isometric leg extension forces in runners. A potential counterproductive outcome of strength training is that muscle hypertrophy could have a negative impact on weight-bearing endurance events. Also, an increase in myofiber cross-sectional area could reduce capillary to muscle fiber cross-sectional area ratio, thus increasing diffusion distance (Aagaard et al. 2010). In this respect supplemental strength training can improve determinants of performance in endurance events by improving the athletes` strength and vertical jump ability without increasing total body mass or compromising the development of V02max. With regards to muscle capillarisation and perfusion, there is no reason to fear that they may be compromised by strength training. Indeed, capillary density does not seem to decrease with strength training in untrained subjects, and concurrent strength and endurance training does not negatively affect muscle capillarisation in trained cyclists (Aagaard et al. 2010). In summary, recent research on highly trained athletes suggests that strength training can be successfully prescribed to enhance endurance performance (Ronnestad & Mujika 2014). The mechanisms involved in the observed performance gains may include a conversion of fast-twitch type IIX fibers into more fatigue resistant type lla fibers, increased muscle strength and rate of force development, and improved neuromuscular function and musculotendinous stiffness, without a change in muscle capillarisation (Aagaard et al. 2011). Vortrag des Referenten auf der Science + Triathlon 2015 World Conference vom 26.-27. November 2015 am INSEP in Paris.
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