MUSCLE ARCHITECTURE AND STRENGTH: ADAPTATIONS TO SHORT-TERM RESISTANCE TRAINING IN OLDER ADULTS TYLER C. SCANLON, MS, 1 MAREN S. FRAGALA, PhD, 1 JEFFREY R. STOUT, PhD, 1 NADIA S. EMERSON, MS, 1 KYLE S. BEYER, BS, 1 LEONARDO P. OLIVEIRA, MD, 2 and JAY R. HOFFMAN, PhD 1 1 Institute of Exercise Physiology and Wellness, University of Central Florida, 4000 Central Florida Boulevard, Orlando, Florida 32816, USA 2 College of Medicine, University of Central Florida, Orlando, Florida, USA Accepted 22 July 2013 ABSTRACT: Introduction: Muscle morphology and architecture changes in response to 6 weeks of progressive resistance train- ing were examined in healthy older adults. Methods: In this randomized, controlled design, muscle strength, quality, and architecture were evaluated with knee extension, DEXA, and ultrasound, respectively, in 25 older adults. Results: Resistance training resulted in significant increases in strength and muscle quality of 32% and 31%, respectively. Cross-sectional area of the vastus lateralis increased by 7.4% (p  0.05). Physiological cross-sectional area (PCSA) of the thigh, a composite measure of muscle architecture, was related significantly to strength (r 5 0.57; p  0.01) and demonstrated a significant interaction after training (p  0.05). Change in PCSA of the vastus lateralis was associated with change in strength independent of any other measure. Conclusions: Six weeks of resistance training was effective at increasing strength, muscle quality, and muscle morphology in older adult men and women. Muscle Nerve 49:584–592, 2014 Aging is associated with progressive loss of neuro- muscular function that often leads to disability and loss of independence. 1 The term sarcopenia, loosely translated, describes a deficiency of flesh (muscle) 2 and is showcased by decreased total muscle cross-sectional area of approximately 40% between the ages of 20 and 60 years. 1 The current diagnosis of sarcopenia is arbitrary in the sense that an individual who has an appendicular skele- tal muscle mass value of 2 standard deviations below that of an age-matched population may be classified as sarcopenic. Age-associated loss of mus- cle mass is often thought to be the cause of strength losses observed with increasing age. Mus- cle size and strength losses are believed to be asso- ciated with metabolic, physiological, and functional impairments. 3 These changes may be attenuated through regular physical activity for the purpose of preserving muscle quality and strength. Muscle function is determined by structure and morphology at the architectural level, 4 where the aging process leads to not only changes in muscle quantity, but also quality. 5 Magnetic resonance imaging is considered the “gold standard” for cross-sectional and muscle volume measures. How- ever, due to the limited availability of magnetic res- onance imaging (MRI), ultrasonography may be a more cost-efficient alternative that is both valid and reliable for assessing large individual human muscle. 6–9 Decreases in muscle quality that are observed commonly in sarcopenia include enhanced intramuscular adipose and connective tissue in addition to decreased lean muscle mass and contractile units. 10 These changes indicate that both muscle quantity and muscle quality can contribute independently to changes in muscle strength in older adults. 11 Muscle quality can be assessed using many methods, which may include relative strength (strength per unit of mass) 12 and muscle composition (relative measures of connec- tive to contractile tissue). 5 Muscle quality can be assessed as echo intensity using ultrasound scan- ning, where an increase in the echo intensity of a muscle represents changes caused by increased intramuscular connective and adipose tissues. 11 Moreover, muscle architecture measures of cross- sectional area, fiber pennation angle, and fascicle length allow for calculation of physiological cross- sectional area (PCSA), a composite measure used to describe the structure–function relationship of muscle. 4 However, no consensus currently exists for methods to calculate PCSA. Some computa- tions exclude variables important for description of the muscle structure–function relationship, such as pennation angle and muscle density. 13,14 Physical exercise is known to result in changes in muscle mass and quality. Resistance training appears to offer greater benefits than aerobic endurance training for gaining muscle mass and improving efficiency of the neuromuscular sys- tem. 10 Evidence suggests that up to 20 years of strength and power losses may be attenuated through regular resistance training. 15 In addition, older adults have demonstrated that the neuro- muscular system has the ability to respond to resist- ance training, which may compensate for not only Abbreviations: 1RM, predicted 1 repetition maximum; BMI, body mass index; CON, control group; CT, computed tomography; DEXA, dual- energy X-ray absorptiometry; EI, echo intensity; L f , fascicle length; LTM, lean thigh mass; MQ, muscle quality as relative strength; MT, muscle thickness; PANG, pennation angle; PCSA, physiological cross-sectional area; REI, relative echo intensity; RF, rectus femoris; ROM, range of motion; RPE, ratings of perceived exertion; RT, resistance training group Key words: echo intensity; exercise; muscle quality; sarcopenia; ultrasonography Correspondence to: Maren S. Fragala; e-mail: maren.fragala@ucf.edu V C 2013 Wiley Periodicals, Inc. Published online 28 July 2013 in Wiley Online Library (wileyonlinelibrary. com). DOI 10.1002/mus.23969 584 Muscle Adaptations MUSCLE & NERVE April 2014