Using Molecular Biology to Maximize Concurrent Tra

Authors: Keith Baar

Publish Date: 2014/10/30

Volume: 44, Issue: 2, Pages: 117-125

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Abstract

Very few sports use only endurance or strength Outside of running long distances on a flat surface and powerlifting practically all sports require some combination of endurance and strength Endurance and strength can be developed simultaneously to some degree However the development of a high level of endurance seems to prohibit the development or maintenance of muscle mass and strength This interaction between endurance and strength is called the concurrent training effect This review specifically defines the concurrent training effect discusses the potential molecular mechanisms underlying this effect and proposes strategies to maximize strength and endurance in the highlevel athleteRobert Hickson was a powerlifter when he went to do his postdoctoral work in the laboratory of Professor John Holloszy Every day Holloszy the father of endurance exercise research would leave the Washington University Medical Campus and go for runs through the adjoining Forest Park In his effort to make a good impression with his new boss Dr Hickson decided to accompany Prof Holloszy on his afternoon runs but soon found that his muscle mass and strength were decreasing in spite of the fact that he was still doing his strength training at the same frequency and intensity When Hickson approached Holloszy with his problem he was told “this should be the first study you do when you have your own lab” True to his word the first study that Hickson completed in his new laboratory at the University of Illinois in Chicago was the seminal study on concurrent trainingPublished in 1980 1 Hickson’s classic study trained three groups of subjects Group 1 performed strength training alone Group 2 performed endurance training alone and Group 3 performed strength and endurance together The strength training was performed 5 days per week for 10 weeks and was designed exclusively to increase leg strength True to his powerlifting background Hickson had his subjects perform all of the exercises with as much weight as possible The endurance training was performed 6 days per week for the same 10week period and consisted of 3 days of cycling and 3 days of running The cycling exercise consisted of six 5min intervals at maximal aerobic capacity VO2max whereas the instructions on the running days were to “run as fast as possible” for 30 min/day in the first week 35 min/day for the second week and 40 min/day for the remainder of the study The concurrent training group performed both the strength and endurance training protocols in a nonstandardized order with between 15 min and 2 h of rest in betweenAt the end of the 10week training program VO2max was determined on the bike and treadmill The strength alone group showed a 4  improvement in VO2max on the bike with no change when measured on the treadmill In contrast the endurance and concurrent training groups both increased VO2max by 17  on the treadmill and ~20  on the bike This indicated that strength training does not negatively affect endurance adaptations or performance It should be noted however that the concurrent training group did not increase their bodyweight over the training period as a result of their strength training If they had it would be expected that their endurance performance could be affected especially during running where they would have to support and propel this extra massThe concurrent training effect on strength The figure shows the increase in one repetition maximum in the squat in subjects who participated in 10 weeks of highintensity resistance exercise alone resistance endurance exercise alone endurance and both types of training concurrent Also note that the strength and concurrent groups both increased their strength together up to 7 weeks when the strength group started making greater gains than the concurrent group adapted from Hickson 1 with permission 1RM one repetition maximumWhen others have repeated the frequency and intensity that Hickson employed in his study they have found a similar attenuation in strength and importantly impaired muscle fiber hypertrophy 2 3 For example Kraemer and colleagues 2 showed that running and strength training at a high intensity for 4 days a week resulted in lower power concomitant with impaired muscle fiber hypertrophy than training for strength alone Strength training alone resulted in ~28  hypertrophy whereas concurrent training resulted in only a ~16  hypertrophy This indicates that concurrent endurance training impairs not only strength but muscle hypertrophy as wellIt is important to note though that when the frequency intensity or duration of training is decreased the degree of interference decreases For example in two separate studies McCarthy and colleagues showed that cycling 3 days a week for 50 min at 70  VO2max was not enough to impair strength 4 or hypertrophy 5 as a result of concurrent strength training Further Sillanpää et al showed that cycling for 30 min twice a week below anaerobic threshold was not enough to impair strength or lean mass in middleaged women 6 or old men 7 Taken together these data suggest that strength and endurance increase concomitantly up to a point However once the frequency increases past 4 days a week or the intensity of endurance exercise increases above 80  VO2max endurance exercise prevents the increase in muscle mass and strength that occurs with strength training This was illustrated nicely in a recent metaanalysis that demonstrated that the effect size of strength training alone on muscle hypertrophy was 122 and for strength was 171 3 The corresponding numbers for concurrent training were 08 and 128 indicating that in a large cohort endurance exercise impairs muscle size and strength adaptations 3Increased strength is the combined effect of improvements in neural activation muscle fiber size and connective tissue stiffness Therefore concomitant endurance exercise could decrease adaptations of any/all of these physiological parameters There does not appear to be a decrease in the neural learning adaptation since in the early stages of training when the neural adaptation is the strongest 4 6 and 8 weeks strength is similar between strength and concurrent training groups 1 2 However it is possible that neuromuscular fatigue plays a role in the decrease in force as training continues At this point no one has measured the effect of concurrent training on connective tissue stiffness so we are unsure of the role of this tissue in the impaired strength response In contrast as stated above there is some evidence that muscle hypertrophy is impaired in individuals training for both strength and endurance together compared with those training exclusively with strength exercises and that this correlates quite well with the impaired strength response 2 3 Therefore the primary effect of endurance exercise seems to be a decrease in resistance exerciseinduced muscle hypertrophy

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