When training older-adult clients, few personal fitness trainers consider adding power as a program design element. However, power is one of the major performance variables associated with independence (Foldvari et al. 2000), fall prevention (Whipple, Wolfson & Amerman 1987) and rehabilitation after injury (Lamb, Morse & Evans 1995) among seniors. Power is also the neuromuscular factor that shows the greatest decline with
aging. For example, from 65 to 89 years of age, the decline in
explosive knee extensor power is 3.5% per year, compared with an annual 1%–2% drop in strength (Skelton et al. 1994). Additionally, Bonnefoy and colleagues (1998) reported that maximal anaerobic power in men declines an average of 8.3% per decade between the ages of 20 and 70. Researchers have also hypothesized that the higher levels of disability in elderly women compared with elderly men is due to the women’s lower power-to-body weight ratios and lesser capacity to produce power (Caserotti et al. 2001; Young & Skelton 1994). This article explores research and techniques for assessing, testing and training for power in older adults, with an end-focus on safely applying high-speed techniques.
What Is Power?
For the purpose of exercise and training, power can be defined in two separate categories: metabolic and mechanical.
Metabolic power is the rate at which the metabolic systems produce energy. The two levels of metabolic power commonly presented in the literature are anaerobic and aerobic. The term anaerobic power is often used synonymously with the term power itself. This leads to misconceptions in both the training description and application. Anaerobic power is the rate at which the creatine phosphate system and anaerobic glycolysis replenish ATP (adenosine triphosphate). It has been estimated that these systems produce energy at, respectively, 75% and 50% of the rate at which the body breaks down ATP, making them the most powerful metabolic systems (Sahlin 1986). Aerobic power is used far less frequently, but nonetheless is the true expression of aerobic fitness. The gold standard for measuring aerobic fitness is the VO2max test, reported in either liters per minute or milliliters per kilogram of body weight per minute. The aerobic energy
system concerns itself with completing the oxidation of glucose/
glycogen originally begun with glycolysis and the breakdown of fat. The estimated power of these pathways is 25% and 12% of the rate of ATP breakdown, respectively (Sahlin 1986).
Mechanical power is most often associated with the performance of activities of daily living (ADL) and with fall prevention. Power is the product of force and velocity. Basic physics teaches that force equals mass times acceleration. A person must overcome force when lifting a free weight. Velocity is a vector that has magnitude (how much?) and direction (which way?). If I try to move a load (mass) that is equal to my one repetition maximum (1RM), my velocity is very slow. Somewhere along the force-
velocity curve there is an optimal load, where the product of force times velocity yields the highest power (see Figure 1).
Why Power Declines With Age
The dramatic reduction in power output after the fifth decade of life is not unexpected, given the changes in both the musculoskeletal and neuromuscular systems. A number of researchers have demonstrated sarcopenia, or an exponential drop in the cross-sectional area of muscle, with aging (Frontera et al. 2000; Lexell 1993) (see Figure 1). It has also been established that the losses are most dramatic in the faster-contracting type II fibers and that the loss of faster-contracting (type II) motor units (muscle fibers and their associated nerves) mirrors the drop in the muscle cross-sectional area (Aniansson et al. 1986; Lexell & Downham 1992). In addition to these changes, reduced motor neuron conduction velocities (Metter et al. 1998), decreased motor nerve myelination (fatty insulation) (Hinman et al. 2006; Jankelowitz, McNulty & Burke 2007), reduced neuromuscular (nerve to muscle) transmission (Cardasis & LaFontaine 1987; Herscovich & Gershon 1987) and decreased levels of excitation-contraction coupling (Delbono, Renaganathan & Messi 1997) have all been reported with aging. Combined, these factors
reduce force production and contractile speed, thereby reducing power production in aging muscle.
The association between power and successful aging is
apparent in the research. As early as 1992, Bassey et al. (1992)
reported that leg extensor power was significantly correlated with measures of daily activities such as chair rises, walking speed and stair climbing. Researchers concluded that leg extensor power assessment should be included as part of any program designed to reduce physical frailty. Skelton et al. (1994) noted that knee extensor power per unit of body weight influenced both chair rise time and step height. Foldvari et al. (2000) found that leg power is a strong predictor of self-reported functional status in older women. Bean et al. (2002) discovered that leg power is an important factor influencing the physical performance of mobility-limited older people. They also noted that although power is related to strength, it is a separate attribute that may exert a greater influence on physical performance. These studies have helped establish the link between power and the maintenance of independence in older persons.
The association between fall prevention and leg power is equally impressive. In 1984, Aniansson et al. (1984), using muscle biopsy techniques, found that hip fracture patients showed significant losses in a muscle cross-sectional area—especially in the faster, more powerful type II fibers. Later, Whipple, Wolfson & Amerman (1987) showed that knee and ankle isokinetic power was the strongest predictor of falls among institutionalized elders. Skelton, Kennedy & Rutherford (2002) found that women who fell had 24% less explosive power in their weaker limb than women who did not fall. They also noted that poor lower-limb explosive power combined with power differences (asymmetry) between limbs might be more predictive of future falls than more traditional measurements of strength in older women living independently. More recently, Sayers et al. (2006) showed that subjects who had slower walking times for the 400-meter (m) walk test reported more falls and had lower leg press power at 70% 1RM and 40% 1RM. These subjects also showed slower leg press contraction velocity at 40% 1RM.
Training for Power
So how do you optimize power development among older-adult clients? In regard to neuromuscular training, the literature has established that high-speed explosive movements (Häkkinen, Komi & Alén 1985; Komi et al. 1982), or at least the attempt to perform high-speed movements (Behm & Sale 1993), are required. Additionally, researchers studying physical performance and aging have recognized that the primary factor dictating power production is movement speed (De Vito et al. 1998; Ferretti et al. 1994; Petrella et al. 2004).
Over the past 15 years the concept of high-speed training to increase power has been applied to older persons. The first presentation examining the positive impact of moderately high speed training on power output in older persons was presented at the American College of Sports Medicine annual meeting in 1993 (Flipse et al. 1993). This preliminary investigation was soon followed by others that demonstrated the positive impact of high-speed training on both power and functional performance (Signorile et al. 1995b; Signorile et al. 1995a). Since then
researchers have reported the successful use of high-speed training to increase both power (Earles, Judge & Gunnarsson 2001; Fielding et al. 2002; Miszko et al. 2003; Signorile et al. 2002) and functional performance (Carmel et al. 2000; Miszko & Cress 2002; Sayers et al. 2003; Orr et al. 2006; Petrella et al. 2007).
However, the use of high-speed training raises a number of important questions:
- What are the equipment/environment choices?
- What are the optimal loads that will maximize power development and ADL performance?
- What are the correct periodized training and testing cycles?
Equipment/Environment Choices. Free-weights, stack-loaded machines, pneumatic machines, tubes, bands and even sandbags have all been successfully used in high-speed training research studies. However, both inertia and momentum must be considered. Inertia is resistance to motion changes, and momentum is mass in motion (defined as mass times velocity). While these terms are often confused with one another, their absolute definitions are not as important as their consequences during high-speed resistance training. Once a client accelerates a weight to a high velocity, the potential for injury at the end range of motion is increased as the weight continues to move and the limb stops. For this reason, devices that reduce momentum, like pneumatics and rubber tubing, are probably safest. If free weights or plate machines are used, it is important to explain to the uninitiated client that he should begin to decelerate the weight well before the end range of motion. Other feasible options are medicine balls (once again, the client must know how to use them properly) and light plyometric work. Aquatic exercises are excellent options, since resistance (drag) increases exponentially with movement speed.
Optimal Loading. This question is not simple to address. Studies have shown that power can be increased in older persons using loads ranging from 20% to 80% of maximum (de Vos et al. 2005; Fielding et al. 2002; Jozsi et al. 1999; Petrella et al. 2007). This can be clarified by understanding that load-velocity relationships during lifting can be changed depending on the goal. For example, researchers have shown that balance and gait speed are more positively affected by loads in the range of 40% of maximum, while chair stands and stair-climbing performance are more affected by loads of approximately 80% of maximum (Cuoco et al. 2004). Additionally, optimal loads may be affected by the nature of the joints being trained. Joints associated with longer bones (e.g., the knee or elbow) are more susceptible to higher training speed than those associated with shorter ones (e.g., the ankle or wrist) (Signorile et al. 2002). The bottom line is that power training can be matched to the diagnosed needs of the individual and the biomechanical capacity of the targeted joints to produce speed.
Periodized Training and Testing Cycles. Finally, proper periodization theory must be considered when training for power. This process begins with training cycles that target hypertrophy and strength. Power training should not be attempted until the client has strengthened her muscles using a hypertrophy, or tissue adaptation, phase. This phase is designed to “toughen” the tissues in preparation for the added stresses of high-speed training. In the University of Miami and Miami Veterans Affairs Medical Center laboratories, this phase usually lasts from 2 weeks (for previously trained persons) to 8 weeks (for frail elders), and it concentrates on gradual strengthening through fluctuating increases in load across time. The preference is to follow this phase with a strength phase, as is the practice in classic periodization cycling, before instituting a power phase. This allows for power training performance at a higher intensity than what would be possible if the strength phase was ignored.
The periodization design should also incorporate work and recovery periods to maximize gains. This allows for increased overload throughout the training period through intermittent periods of recovery (lower-intensity training). Using ADL-
specific training during these low-intensity recovery cycles “translates” increases in power to improvements in both ADL performance and fall prevention. Practicing ADL movements—such as gait and ladder drills, object movement drills, and drills concentrating on static and dynamic balance—allows the client to use his increased neuromuscular capacity during motor patterns that are meaningful to daily living (Signorile 2005). In fact, ADL-based training has been shown to be more effective than strength training in improving ADL performance in a number of recent studies (de Vreede et al. 2004; de Vreede et al. 2005). There should be sufficient taper at the end of each recovery period to evaluate the client’s progress and modify the program for the next training cycle.
If your goal as a personal fitness trainer is to increase
independence and reduce the probability of falls in older clients, consider power training as part of the program. No single workout or exercise device can address the diverse physical factors associated with successful aging. Provide power training cycles in a properly designed periodization model with other cycles, such as hypertrophy, strength and endurance cycles. Determine the need to target specific muscles and/or ADL-based activities using the testing procedures presented (see “Testing for Power” on page 39). Here is a sample process for a new client:
- Perform an initial testing session to provide a baseline and
assess specific needs.
- Provide a hypertrophy (tissue adaptation) phase and a strength cycle prior to the high-speed power cycle.
- Apply the load that is specific to the need (lower for walking speed, greater for stand-up decrements).
- Use proper intensity and volume cycling, followed by an ADL-specific, motor skill–based taper period in preparation for retesting and the next cycle.
By understanding the proper application of high-speed training techniques, personal fitness trainers can help older individuals improve their functional status effectively and safely.
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