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  1. #1
    Join Date: Apr 2011
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    Combining Cardio With Resistance Exercise: Muscle Growth Killer?



    Combining Cardio With Resistance Exercise: Muscle Growth Killer?
    By Robbie Durand, M.A.



    You just finished a grueling session of working out and now it?s time to do some cardio. Wait? combining cardio with resistance exercise may hinder muscle growth, according to a new study.

    In the Journal of Applied Physiology, researchers reported that if you are trying to gain muscle mass, combining resistance exercise and cardio in the same session may disrupt genes for anabolism.4 It has been shown that repeated high-intensity, short-duration contraction promotes muscle hypertrophy and strength gains,1, 2 whereas prolonged, low-intensity contractile activity is associated with increased mitochondrial density and enhanced resistance to fatigue (an aerobic muscle fiber type).3 Previous research observed only modest hypertrophy with endurance training, combined with resistance exercise in skeletal muscle of subjects.



    Type of Exercise Influences Gene Expression

    Researchers from Australia, in a study published in Medicine and Sports Science and Exercise, examined genes from well-trained endurance athletes and resistance-trained athletes to determine if a particular type of exercise turns ?on? different genes. Twenty healthy males volunteered for this investigation. Seven were endurance-trained cyclists who had been training for eight years (cycling 250-600 kilometers per week). These subjects had no history of strength/resistance training. Six subjects were strength-trained (ST) powerlifters who had been strength/resistance training exclusively for nine years (three to four sessions per week).

    As might be expected, genes chronically altered in endurance subjects are predominantly involved in energy metabolism and mitochondrial function, membrane transport, and blood vessel growth, whereas those upregulated by prolonged strength training are involved in processes that regulate protein synthesis and transcription and translation. The research group reported for the first time that a great number of genes that regulate these processes are chronically elevated, specific to this type of training.

    Strength-trained individuals, on the other hand, are characterized by muscle hypertrophy/protein synthesis, which is reflected in the novel genes and the gene clusters upregulated. These data support the notion that regular strength training chronically alters skeletal muscle gene expression to promote protein synthesis and hypertrophy, thus maintaining the phenotype for improved muscle force production. In contrast, the endurance training phenotype has a strong association with aspects related to mitochondrial biogenesis, improved oxygen supply, and energy metabolism. The novel genes and the gene clusters highlight the chronic upregulation of genes specific to the characteristic phenotype for efficient energy provision from metabolism during rhythmic, continuous muscle contractions in endurance exercise.

    In summary, there is evidence that basal gene expression patterns in human skeletal muscle are altered after chronic (greater than eight years) endurance and strength training. In particular, training-specific differences exist in groups of genes that are involved in adaptive processes that are important in response to different types of training.5 On the basis of this perspective, it is probable that chronic training subtly regulates numerous genes from important functional groups in human skeletal muscle, possibly through modulation of processes that control mRNA degradation, as a long-term adaptive mechanism to cope with repeated training stimuli.



    What Happens If You Combine Aerobic and Resistance Exercise In the Same Session?

    If doing certain exercises turns on specific genes, then combining exercises may result in a ?mixed? signal in muscle. Therefore, the possibility exists that the cumulative, adaptive effect with consecutive resistance and endurance exercise bouts results in an ?interference effect? with concurrent training. This means that cardiovascular training turns on genes for an aerobic fiber type (increased type I fibers, increased mitochondria), while resistance exercise turns on a resistance training gene phenotype in muscle (increased type IIAB muscle fibers, increased anaerobic threshold, etc.). By combining the two, you have a ?mixed? gene expression being translated in muscle.

    Researchers from Australia took trained men and assigned them to either one of two conditions. One experimental trial consisted of a bout of resistance exercise followed by a bout of endurance exercise (cycling), while in the other trial, subjects performed the reverse exercise order (i.e., endurance, then resistance exercise).

    ? Following a standardized warm-up (2 x 5 repetitions at 50 percent and 60 percent of 1RM, respectively), subjects performed 8 sets of 5 repetitions at ~80 percent of 1RM. Each set was separated by a 3-minute recovery, during which the subject remained seated on the leg extension machine.

    ? Subjects performed 30 minutes of continuous cycling at a power output that elicited ~70 percent of individual VO2 peak.

    Muscle biopsies were taken before, 15 minutes after, and 3 hours after exercise.



    Combining Cardio and Resistance Exercise Disrupts Genes for Anabolism

    Basically, it?s a ?no win? situation no matter which way you look at it. Combining cardio and resistance exercise disrupted genes for muscle anabolism. For example, here is what the researchers found when genes were analyzed.

    ? Cardio Before Resistance Exercise: A novel finding was that an endurance bout undertaken prior to resistance exercise suppressed IGF-1 Ea (a gene splice of IGF-1) mRNA (~42 percent) and also induced small declines in mechano growth factor (~27 percent). The findings represent the collective effect of diverse contraction modes, and it is tempting to speculate that endurance exercise immediately preceding resistance exercise attenuates anabolic response.

    ? Resistance Exercise, Then Cardio: Cardio performed after resistance exercise increased genes for muscle tissue breakdown. Muscle breakdown genes were elevated (atrogin, 21 percent and MuRF mRNA, 53 percent) when cycling was performed subsequent to resistance exercise. Previous studies showed that following a single bout of endurance exercise, atrogin and MuRF mRNA (genes for muscle tissue breakdown) were elevated. Thus, the results indicate that endurance activity after resistance training may have the capacity to exacerbate genes for catabolism and subsequent protein degradation. Consequently, when resistance exercise is undertaken after endurance exercise, upregulation of ubiquitin ligase expression may be suppressed. Moreover, PGC-1-alpha mRNA? a gene that turns ?on? an aerobic phenotype? was elevated when cycling preceded resistance exercise.

    The results indicate that endurance activity prior to resistance exercise may diminish anabolic response, while endurance activity after resistance exercise may exacerbate inflammation and protein degradation. AMPK has been termed a metabolic ?master controller? activated by exercise and changes in glycogen content in skeletal muscle. AMPK activation was not different 15 minutes after each successive exercise bout. However, AMPK above resting baseline was higher 3 hours after cycling was done after resistance exercise, indicating metabolic stress may have been exacerbated when endurance exercise was performed subsequent to resistance exercise.

    The results provide support for the contention that (acute) combination of cardio and resistance exercise training back-to-back does not promote optimal activation of anabolic pathways.4 Thus, undertaking both resistance exercise/cardio together in close proximity influences the acute molecular profile and likely exacerbates acute ?interference? of key anabolic-signaling pathways.

    One of the things I was highly critical of in this paper was that after exercise, the subjects did not eat for 3 hours? a huge flaw in the study. I contacted Dr. Hawley and he said that this was a preliminary study, and researchers have samples where the subjects consumed a post-exercise protein/carbohydrate shake to see if there was a different effect on the genes in muscle. The study is set to be released in a few months.

    If you going to do cardio, it may be better? for an optimal anabolic effect? to do it earlier or later in the day, as opposed to doing it before or after resistance exercise.





    References:

    1. Fry AC, Schilling BK, Staron RS, Hagerman FC, Hikida RS, Thrush JT. Muscle fiber characteristics and performance correlates of male Olympic-style weightlifters. J Strength Cond Res, 17: 746-754, 2003.

    2. Tesch P, Komi P, Hakkinen K. Enzymatic adaptations consequent to long-term strength training. Int J Sports Med Suppl, 8: 66-69, 1987.

    3. Hawley JA. Adaptations of skeletal muscle to prolonged, intense endurance training. Clin Exp Pharmacol Physiol, 29: 218-222, 2002.

    4. Coffey VG, Pilegaard H, Garnham AP, O'Brien BJ, Hawley JA. Consecutive bouts of diverse contractile activity alter acute responses in human skeletal muscle. J Appl Physiol, 2009 Apr;106(4):1187-97.

    5. Stepto NK, Coffey VG, Carey AL, Ponnampalam AP, Canny BJ, Powell D, Hawley JA. Global gene expression in skeletal muscle from well-trained strength and endurance athletes. Med Sci Sports Exerc, 2009 Mar;41(3):546-65.


  2. #2



    good read. Thanks.


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