Research Update

Here is last month's research update from FitBits.

FitBits
March 15, 2006
Exercise ETC’s Review of Exercise Related Research
Compiled by Jeannie Patton, MS, CSCS

Visualization improves muscular force development

Mental practice has been shown to be effective in increasing the force production of the smaller muscles in the hand. The aim of this study was to determine whether mental practice could produce force gains in the larger ankle dorsiflexor muscles, which are so important during walking.

Twenty-four subjects were randomly assigned to a physical practice group, a mental practice group, or a control group. In the practice groups, subjects either physically or mentally practiced producing maximal isometric contractions for 3 sets of 10 repetitions, 3 times per week for 4 weeks. Changes in mean peak isometric strength and the resulting percentage of improvement were analyzed across the 3 groups. Interestingly, visualization produced gains in muscular force: both the physical exercise group and the visualization group saw significant increases in improvement (25% & 17% respectively) but the control group did not. These findings show that mental practice in people without impairments can lead to an increase in force production similar to that produced by physical practice. Fitness Professionals should consider mental practice as a useful adjunct to traditional training options aimed at increasing muscle strength.

Sidaway, Ben & Trzaska, (Robinson) Amy. Can Mental Practice Increase Ankle Dorsiflexor Torque? Journal of Physical Therapy. 2005, 85(10), 1053-1060.


Men are stronger because they have more muscle mass, not stronger muscle fibers

Power production is a function of both muscle strength and contractile speed and the ability to generate power is critical to performing many activities of daily living. Older women have greater limitations in function than men and a longer period of dependence before death. The objective of this study was to directly compare whole muscle and single muscle fiber power production in older men and women.

Sixteen older men and women (mean age 72) served as subjects. Needle biopsy of the vastus lateralis was performed in order to isolate single muscle fibers. Researchers studied 274 type I and 33 type IIa muscle fibers. Whole muscle strength and power was measured using knee extension and double leg press. Results showed men had greater whole muscle strength, power and velocity than women, however in single muscle fiber comparison, no significant differences in power-generating capacity were found in either type I or type IIa fibers.

These results indicate that the observed differences in strength and power between men and women are more a result of greater muscle mass in men than women as well as, possibly, differences in central nervous system activation. Studies such as this are important to Fitness Professionals to understand what causes power decline in older women and to help in developing programs to improve function and reduce decline during aging.

Krivickas, Lisa. et al. Sex differences in single muscle fiber power in older adults. Medicine & Science in Sports & Exercise. 2006, 38(1), 57-63.


Carb supplementation makes no difference in RPE during resistance training

It is generally thought that carbohydrate availability mediates the rate of perceived exertion (RPE) during endurance exercise but it is currently not known if carbohydrate supplementation would also mediate RPE during resistance training. The purpose of this study was to determine the relationship between carbohydrate supplementation and RPE during resistance training.

Thirty strength-trained subjects took either a carbohydrate supplement or a placebo and lifted weights for 2 hours. The subjects performed 4 sets of 10 repetitions for 10 exercises with a 2 to 3 minute rest intervals between set; RPE was taken following the last repetition of each set for each exercise.

The study results showed that carb supplementation had no effect on RPE during resistance training, so it can be concluded that factors mediating RPE may be different between resistance exercise and endurance exercise. Fitness Professionals may still want to consider the use of carbohydrate supplementation for athletes and clients who train like athletes; it may not make the resistance exercise feel any easier, but it may provide other physiological benefits such as increased recovery rates between training days. Following training, carbohydrate availability is essential for increasing the rate of liver and muscle glycogen resynthesis.

Utter, Alan, C. et al. Carbohydrate supplementation and perceived exertion during resistance exercise. National Strength & Conditioning Journal. 2005, 19(4), 939-943.


Dual-task balance improved by specific types of balance training

Traditionally, rehabilitation programs emphasize training balance under single-task conditions to improve balance and reduce risk for falls. The purpose of this case report is to describe 3 balance-training approaches in older adults with impaired balance.

The three patients studied were older adults who volunteered for balance training because of a self-reported history of falls in the previous year or because of a concern about impaired balance. They were randomly assigned to one of 3 conditions that involved either a single task activity or dual task activity. The single-task conditions were: (1) narrow walking and (2) stepping over obstacles; the dual-task conditions were: (1) narrow walking while counting backward by "threes," (2) stepping over obstacles while counting backward by threes, (3) narrow walking while distinguishing whether an auditory tone was high or low, (4) stepping over obstacles with auditory tone discrimination. Training sessions consisted of 45 minutes, 3 days per week for 4 weeks. The patients who received balance training under dual-task conditions showed dual-task training benefits which were maintained for 3 months.

Older adults may be able to improve their balance under dual-task conditions only by following specific types of balance training. Since most activities of daily living involve dual-task conditions (i.e., walking while carrying groceries, walking while turning the head to cross a street etc.) Fitness Professionals should use this information to make their balance training more task specific.

Silsupadol, Patima et al. Training of Balance Under Single- and Dual-Task Conditions in Older Adults With Balance Impairment. Journal of Physical Therapy. 2006, 86(2), 269-281.