Article

Age and sex affect human muscle fibre adaptations to heavy-resistance strength training

Department of Physical Therapy, University of Maryland Eastern Shore, Princess Anne, MD 21853, USA.
Experimental Physiology (Impact Factor: 2.87). 03/2006; 91(2):457-64. DOI: 10.1113/expphysiol.2005.032771
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ABSTRACT This study assessed age and sex effects on muscle fibre adaptations to heavy-resistance strength training (ST). Twenty-two young men and women (20-30 years old) and 18 older men and women (65-75 years old) completed 9 weeks of heavy-resistance knee extension exercises with the dominant leg 3 days week(-1); the non-dominant leg served as a within-subject, untrained control. Bilateral vastus lateralis muscle biopsies were obtained before and after ST for analysis of type I, IIa and IIx muscle fibre cross-sectional area (CSA) and fibre type distribution. One-repetition maximum (1-RM) strength was also assessed before and after ST. ST resulted in increased CSA of type I, IIa and IIx muscle fibres in the trained leg of young men, type I and IIa fibres in young women, type IIa fibres in older men, and type IIx fibres in older women (all P<0.05). Analysis of fibre type distribution revealed a significant increase in the percentage of type I fibres (P<0.05) along with a decrease in type IIx fibres (P=0.054) after ST only in young women. There were no significant changes in muscle fibre CSA or fibre type distribution in the untrained leg for any group. All groups displayed significant increases in 1-RM (27-39%; all P<0.01). In summary, ST led to significant increases in 1-RM and type II fibre CSA in all groups; however, age and sex influence specific muscle fibre subtype responses to ST.

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    • "Histological studies also indicated that age-related changes in fiber type composition may affect muscle strength negatively (Korhonen et al., 2006; Martel et al., 2006). In our study, we observed significantly higher Pi/ATP ratios in the late-middle-age group indicating reduced type II fiber fraction (Madhu et al., 1996). "
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    ABSTRACT: During aging declining maximum force capacity with more or less unchanged fatigability is observed with the underlying mechanisms still not fully understood. Therefore, we compared morphology and function of skeletal muscles between different age groups. Changes in high-energy phosphate turnover (PCr, Pi and pH) and muscle functional MRI (mfMRI) parameters, including proton transverse relaxation time (T2), diffusion (D) and vascular volume fraction (f), were investigated in moderately exercised low back muscles of young and late-middle-aged healthy subjects with (31)P-MR spectroscopy, T2- and diffusion-weighted MRI at 3T. In addition, T1-weighted MRI data were acquired to determine muscle cross-sectional areas (CSA) and to assess fat infiltration into muscle tissue. Except for pH, both age groups showed similar load-induced MR changes and rates of perceived exertion (RPE), which indicates comparable behavior of muscle activation at moderate loads. Changes of mfMRI parameters were significantly associated with RPE in both cohorts. Age-related differences were observed, with lower pH and higher Pi/ATP ratios as well as lower D and f values in the late-middle-aged subjects. These findings are ascribed to age-related changes of fiber type composition, fiber size and vascularity. Interestingly, post exercise f was negatively associated with fat infiltration with the latter being significantly higher in late-middle-aged subjects. CSA of low back muscles remained unchanged, while CSA of inner back muscle as well as mean T2 at rest were associated with maximum force capacity. Overall, applying the proposed MR approach provides evidence of age-related changes in several muscle tissue characteristics and gives new insights into the physiological processes that take place during aging. Copyright © 2015. Published by Elsevier Inc.
    Experimental Gerontology 03/2015; 65. DOI:10.1016/j.exger.2015.02.016 · 3.53 Impact Factor
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    • "Thus, the 8-week duration of RW activity applied at 16–17 months of age in this study may not have delivered a strong enough metabolic or biomechanical stimulus for MHC isoform modulation or myohypertrophy . A number of studies indicate that the hypertrophic response of muscle may be blunted with aging (Degens and Alway 2003; Martel et al. 2006). It may also be the case that the same duration of activity applied at an earlier age could promote persistent myohypertrophy throughout older age, as suggested by studies of testosterone injections at early middle age in mice (Egner et al. 2013). "
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    02/2015; 3(2). DOI:10.14814/phy2.12319
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    • "During aging there is a progressive loss of skeletal muscle mass and function (Ballak et al., 2014; Degens and Korhonen, 2012). While resistance exercise is a widely used strategy to counteract the age-related loss in muscle mass and strength (Brown et al., 1990; Frontera et al., 1988; Leenders et al., 2013), the hypertrophic response to resistance training or overload may be blunted in old humans (Grimby et al., 1992; Kosek et al., 2006; Martel et al., 2006; Raue et al., 2009; Slivka et al., 2008) and rodents (Alway et al., 2002a; Blough and Linderman, 2000; Degens and Alway, 2003). It has been postulated that the agerelated blunted hypertrophy is largely due to a decrease in the number of functional myofibers (Degens, 2012), but a reduced ability of old myofibers to hypertrophy may also contribute. "
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    Experimental Gerontology 01/2015; 62:23-31. DOI:10.1016/j.exger.2014.12.020 · 3.53 Impact Factor
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