Space Shuttle and International Space Station (ISS) crew members have experienced decreases in muscle strength and endurance as a result of space flight. Historically, NASA has used isokinetic strength testing of the lower extremity as its primary method of pre- and post flight muscle strength testing. Isokinetic strength testing uses a dynamometer to measure joint torque at selected angular velocities, and is safe for clinical research. However, functional tasks conducted in 1-G, such as walking and running, require muscle contraction at variable joint velocities, accelerations, and variable resulting forces. It has been suggested that free weight testing is a better testing mode for the evaluation of functional muscular strength. Additionally, it has been suggested that free weight testing is a valid and a safe mode of testing for various populations.
MuscleLab (Ergotest Technology, Langesund, Norway) is a commercial device that measures the lifting velocity and calculates the average power output of a barbell during free weight strength testing. The device consists of a linear encoder that can be attached to a bar or sliding rack to track displacement and velocity. A "user-friendly" software program uses the known mass of the bar and measured velocity to calculate average power. MuscleLab (ML) also uses power from sub-maximal lifts to estimate a one-repetition maximum lift (1-RM). ML is already used by ESA to test their astronauts for changes in power.
Investigators evaluated free weight muscle power testing with ML to determine it's usefulness for CSE testing. The objectives of the study were:
The investigators hypothesized that average power measured using the ML would be valid and reliable and that the greatest average power would be produced during lifts at 50% of the subject's 1-RM. Investigators also hypothesized that the 1-RM calculations provided by the device's software would be accurate within 5-7%.
Power testing was conducted using MuscleLab. In addition, the SMART Optoelectric Motion Analysis System (BTS Engineering, Padova, Italy) was used to measure the velocity of movement during bench press (BP) and leg press (LP). The BP was conducted on a Smith machine made by Cybex International Inc. (Medway, MA), while the LP was conducted on a 45° angled sled from Cybex International Inc.
The study was comprised of two phases. During Phase I, subjects performed BP, while during Phase II, subjects performed LP. In each phase, they participated in a total of six testing sessions conducted on six separate days. At least 48 hours of rest separated each testing session. During sessions one, two, and three, subjects performed a series of lifts to establish their actual one-repetition maximum (1-RM). During sessions four, five, and six, subjects performed explosive lifts at 30, 40, 50, 60, 70, and 80 percent of their highest measured 1-RM.
Before each test, the subjects warmed up on a cycle ergometer for five minutes and then stretched the chest and arm musculature. During the 1-RM tests, subjects lifted gradually increasing loads until they were unable to perform a complete repetition of a lift. A weight was declared a subject's 1-RM when the subject was unable to lift a heavier weight. The 1-RM tests were performed according to the guidelines outlined by Stone and O'Bryant (1986).
During sessions four, five, and six, subjects performed explosive lifts at percentages of their highest measured 1-RM. After a sufficient warm-up, each subject performed one set of three repetitions at loads of 30, 40, 50, 60, 70, and 80 percent of the peak actual 1-RM. During BP testing, the subject lowered the bar to the chest in a controlled manner, touched the chest, and then accelerated the bar upward to the highest bar position as fast as possible. During the BP lifts, subjects were not permitted to throw the bar from the hands. During the LP, the subject lowered the sled to the chest in a controlled manner and then accelerated the sled to the top position as fast as possible. Subjects were encouraged to accelerate through the full range of motion and to allow the sled to leave the feet.
The average bench press (BP) power measurements were highly reliable. No significant difference in average power during the BP was found between sessions one, two, and three. However, the average power produced in repetition one was greater than the power produced in repetition three. The average power at 30 and 80 percent of the subject's 1-RM was similar, but the power at 40, 50, 60, and 70 percent was significantly different from one another. The greatest average power output during the BP was produced at 60% of the subject's 1-RM.
The average leg press (LP) power measurement was highly reliable. No significant difference was found between sessions. For LP, power was lower for repetition three than for repetition one. The highest power was achieved at 60% of the subject's 1-RM. However, powers at 50 and 60 percent of 1-RM were not significantly different. Also, 50 and 70 percent were similar to each other, but 70% was significantly different from 60%. The peak average powers produced at 40 and 80 percent were similar. All other loads were significantly different from each other.
Findings suggest that MuscleLab (ML) is a reliable device for measuring average power. However, the data are not valid when compared with motion capture. ML was accurate in estimating BP and LP 1-RM using certain combinations of submaximal power lifts. Although ML is a reliable device for measuring average power for BP and LP, it should not be used for 1-RM predictions with LP or to report accurate power outputs.
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