Modest Enhancement of Knee Extensor MVC Strength and EMG Activity When the Body Is Tilted Backwards: 2306: Board #185 June 3 2:00 PM - 3:30 PM

Zhao, Zuowei; Fridenmaker, Steven M.; Warren, Gordon L. FACSM

Medicine & Science in Sports & Exercise: May 2010 - Volume 42 - Issue 5 - pp 580-581
doi: 10.1249/01.MSS.0000385443.73837.dc
D-34 Free Communication/Poster - Neural Control of Movement and Balance: JUNE 3, 2010 1:00 PM - 6:00 PM: ROOM: Hall C

Georgia State University, Atlanta, GA.


(No disclosure reported)

Two recent studies have reported that maximal voluntary contraction (MVC) strength and electromyographic (EMG) activity of the elbow flexors and knee extensors are reduced in subjects tested in an inverted body position. However, there is little research regarding the effects of less extreme changes in body position on muscle strength and activation.

PURPOSE: To evaluate the effect of four different body positions in the sagittal plane on MVC strength, percent muscle activation, and EMG activity of the knee extensor muscles.

METHODS: Twenty healthy subjects (mean age: 28 years, 14 males and 6 females) were tested using a modified Nautilus NT-1260 knee extension/leg curl machine in the following positions: trunk tilted either 22.5o forward, 22.5o backward, 45o backward, or 0o (neutral). The hip and the knee angles were fixed at 90o and 70o, respectively. MVC strength and percent muscle activation were measured using the interpolated twitch procedure. Surface EMG was recorded during knee extensor MVC for the vastus medialis, vastus lateralis, biceps femoris, and semitendinosus/semimembranosus muscles.

RESULTS: MVC strength increased progressively by 5% in going from the 22.5o forward to the 45o backward position (P = 0.037). EMG activity during MVC showed a similar trend. For the vastus lateralis, peak EMG root-mean-square (RMS) increased progressively by 8% in going from the 22.5o forward to the 45o backward position (P = 0.007). However, there were no significant differences among the four body positions in knee extensor percent muscle activation during MVC. As the body was tilted backwards, there was also increased co-contraction of the hamstrings with the semitendinosus/semimembranosus EMG RMS increasing from 12% to 14% of maximal (P = 0.005).

CONCLUSION: This study indicates that over the 67.5o range tested in the sagittal plane, there are minor effects of body position on MVC strength and EMG activity of the knee extensors.

© 2010 American College of Sports Medicine