Power Training: Can it Improve Functional Performance in Older Adults? A Systematic Review. JOHN RICE †1, JUSTIN W.L. KEOGH ‡1,2 1School of Sports and Recreation, AUT University, Auckland, New Zealand; 2Centre for Physical Activity and Nutrition Research, AUT University, Auckland New Zealand †Denotes graduate student author, ‡denotes professional author ABSTRACT Int J Exerc Sci 2(2): 131-151, 2009. Older adults’ reduced performance in functional activities of daily living (ADL) such as gait, sit to stand or stair climbing may reflect age-related declines in muscular power more so than strength. Therefore, this review was conducted to determine if power training is effective in improving the functional ability of older adults, and if so, if it was more effective than strength training. The review was performed using Medline (PubMed), CINAHL, Sports Discus, ProQuest 5000 International and Google Scholar with the keywords “power training”, “older adult” and “elder” and all derivatives. Of the 12 eligible studies identified, nine also included a strength training group. Virtually all studies reported significant increases in strength and power for the strength and power training groups. Significant improvements in functional performance were observed for the power training groups in 10 of the 12 studies and in the strength training group in four of the nine studies that also examined the effect of strength training. These results demonstrate that strength and power training can both significantly improve functional performance in older adults, and suggest that power training may be more effective than strength training in this regard. Future research in this area should involve larger sample sizes of older men and women with varying levels of pre-training strength, power and functional ability and: 1) compare the relative efficacy of strength and power training; 2) determine if the optimal training prescription differs somewhat for each functional task; and 3) examine changes in quality of life and falls rate. KEY WORDS: activities of daily living; elders; exercise; functional ability; resistance training; review. INTRODUCTION climbing, walking, rising from a low chair and lifting and carrying objects with The Importance of Functional relative ease and without assistance. Independence However many studies have shown that Successful aging for many older adults the aging process results in significant includes the ability to live functionally losses to functional ability (50, 70, 77). independent, fully engaged lifestyles While this loss in functional ability may within the community. This may involve reflect many age-related changes in the ability to perform functional tasks or neuromuscular system function, it tends to activities of daily living (ADL) such as stair be strongly associated with the onset of POWER TRAINING AND OLDER ADULTS sarcopenia, which is defined as the power, and that methods that increase significant loss of muscle mass typically strength and/or power might be useful in seen in many older adults (13, 34). improving the functional ability of older adults. Numerous research studies utilizing more traditional progressive resistance training Strength is generally measured in Newtons approaches have focused on the (N) or kg and represents the greatest load development of muscular strength and lifted during a one repetition maximum increased muscle mass to slow or reverse (1RM) or the greatest force recorded in a the effects of sarcopenia in older adults. maximum voluntary isometric contraction Although this type of slow to moderate- (MVC). By virtue of the force-velocity velocity resistance training can improve relationship, 1RM and MVC strength older adults’ muscle mass, strength and assessments are performed at a very low high-load power (9, 23, 27, 40), this may not and zero velocities, respectively. Power is necessarily equate to improvements in the defined as the product of force (strength) performance of ADL (71). Such results and velocity (speed). The force-velocity have lead a number of research groups to relationship therefore indicates that power suggest that power training may be more output is typically maximised with effective in improving older adults’ moderate loads as they allow moderate to functional ability and reducing their falls moderately high levels of both force and risk than regular strength training (34, 38). velocity to be produced (18). Consequently, the primary aims of the current review were to determine if power As high level functional performance is training: 1) can significantly improve the typically characterized by the ability to functional ability of older adults in ADL move quickly, it could be theorized that such as level gait, sit to stand and stair muscular power output may be of greater climbing; and 2) is better than strength importance than strength to older adults. training in this regard. This is supported by the results of numerous studies which have shown that Relationship between Muscular Strength, muscular power is more closely associated Power and Functional Performance in to performance in functional ADL that are Older Adults essential to independent living (8, 17, 19, 25, Alexander and colleagues (1) reported that 29, 61). Cuoco and colleagues (19) in rising from a chair an older adult has to demonstrated that leg muscle power was use a greater percentage of their knee more highly correlated to older adults’ extensor strength and power (35-87%) than performance in ADL such as stair climbing, a younger adult (19-49%). Such results rising from a chair and walking than was suggest that the maintenance of strength 1RM strength. Similarly, Clemencon et al. and power by older adults is important if (17) found that older adults’ performance of functional ability and independence is to be the sit to stand, 6 m walk and stair climb maintained. Such results suggests that the was highly predicted by their muscular age-related decline in functional ability is power and optimal velocity, where optimal associated with the loss of strength and velocity was defined as the velocity at International Journal of Exercise Science 132 http://www.intjexersci.com POWER TRAINING AND OLDER ADULTS which peak power occurred. Other studies these age-related declines it is important to have also demonstrated that decreases in understand the mechanism(s) responsible muscular power are associated with an for these changes. While the relative increased risk or incidence of falls (16, 72, importance of each mechanism is not well 76). Overall, these results suggest that an understood, it appears that the age-related improvement in the functional ability of decline in muscle strength, power, velocity older adults may be realized by increasing and force control arise from a number of their lower body muscular power output. similar degenerative processes affecting the To maximize the effectiveness and safety of muscular and neural systems (13, 24, 64). the exercise prescription it is imperative that it is based on sound physiological and One of the leading causes of this age-related biomechanical principles and is designed to decline in muscle function is believed to be counteract the primary mechanism(s) sarcopenia, which is defined as a reduction underlying the age-related changes in in muscular cross sectional area (CSA) (13). power and functional ability. Sarcopenia directly results from the atrophy or death of individual muscle fibres, Physiological Changes with Aging particularly a reduction in the proportion, Aging is associated with a progressive number and size of fast twitch (Type IIa decline in overall neuromuscular function. and IIb) muscle fibres/motor units (26, 47). For example, from the age of 60 years, older Fast-twitch, especially Type IIb muscle adults may experience a decrease in fibres are able to produce larger forces and muscular strength and power of 1.4-2.5% contract at a higher velocity than Type I and ~3.5% per year, respectively (7, 30, 44, fibres (54). Thus, a reduction in the 59). The greater age-related loss of muscle proportion, number and/or size of fast- power than muscle strength would appear twitch muscle fibres will substantially to be a result of the definitions of each term. reduce the force potential (strength) and As power is the product of force and velocity of contraction, leading to even velocity, a small reduction in both force and larger reductions in power than for strength velocity would result in a greater loss of or speed alone (35, 44, 52). power than that of force or velocity, respectively. For example, if an older adult A range of neural factors also appear experiences a 30% loss of both force and associated with the age-related reduction in velocity, they only have 70% of their muscle function. These may include a loss original strength and movement speed. of neural drive, altered motor unit firing This now means they now have only 49% of characteristics, increased co-activation and their original muscular power. an inability to recruit all motor units (24, 49). Collectively, these neural changes The age-related loss of neuromuscular reduce the ability of the older adult to function also causes a significant reduction utilize the full force- and velocity- in older adults’ movement speed and force generating capabilities of their muscular control (49, 52), although the rate of change system. in these abilities are less well described than for strength and power. To attenuate International Journal of Exercise Science 133 http://www.intjexersci.com POWER TRAINING AND OLDER ADULTS While research studies continues to be manner in which older adults walk and performed to determine the extent to which climb stairs may also be compromised the age-related decline in the various leading to an increased risk of falls (77). components of the neuromuscular system Their gait is often characterized by a may cause the reduction in muscle reduction in the support moment (sum of function, any decline in these systems can ankle, knee and hip moments), decreased reduce the strength, power, speed and force stride length and an increase in ground control of older adults.