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Time-to-Fatigue and Intramuscular pH Measured via NIRS During Handgrip Exercise in Trained and Sedentary IndividualsIn exercising muscles force production and muscular endurance are impaired by a decrease in intramuscular pH. The effects of aerobic training (AT) on preventing acidosis and prolonging exercise time in muscles not specifically targeted by the training are unknown. Purpose: To compare interstitial pH, measured non-invasively with near infrared spectroscopy (NIRS), in the flexor digitorum profundus (FDP) during rhythmic handgrip exercise in sedentary subjects and those who participate in AT activities that target the lower body. Methods: Maximal isometric force (MIF) was measured on three separate days in AT (n=5) and sedentary (n=8) subjects using a handgrip dynamometer (HGD). Isometric muscular endurance (IME) was measured during five trials, each separated by at least 48 hrs. For each IME trial subjects rhythmically squeezed (4 sec at 40% of MVC) and relaxed (2 sec) to fatigue or failure to reach the target force in three consecutive contractions or four non-consecutive contractions. Interstitial pH was derived from spectra collected using a NIRS sensor adhered to the skin over the FDP. The first four IME trials served to familiarize subjects with the protocol; the fifth trial was used for analysis. NIRS-derived pH was averaged in 30 sec increments. Between group differences in MIF and exercise time were tested using paired t-tests. A repeated measures ANOVA was used to analyze effects of AT and exercise time on pH. Results: MIF was not different between groups (mean SD; aerobic=415.6 95.4 N vs. sedentary =505.1 107.4 N). Time to fatigue was greater in the AT than in the sedentary group (mean SD: 611 173 sec vs. 377 162 sec, p<0.05). pH was not different between groups at any time point. Average pH decreased (p<0.05) in both groups from rest (pH=7.4) through 90 sec of exercise (pH=6.9), but did not decrease further throughout the remainder of exercise. Conclusion: Although between group differences in pH were not detected, differences during the onset of exercise may exist with a more frequent sampling. AT individuals appear to better tolerate decreased interstitial pH and are able to continue submaximal muscular work, possibly due to psychological familiarization to muscular fatigue and/or systemic physiological benefits.
Document ID
20080043913
Acquisition Source
Johnson Space Center
Document Type
Presentation
Authors
Everett, M. E.
(Houston Univ. TX, United States)
Lee, S. M. C.
(Wyle Integrated Science and Engineering Group Houston, TX, United States)
Stroud, L.
(Wyle Integrated Science and Engineering Group Houston, TX, United States)
Scott, P.
(UMmass Medical School Worcester, MA, United States)
Hagan, R. D.
(NASA Johnson Space Center Houston, TX, United States)
Soller, B. R.
(UMmass Medical School Worcester, MA, United States)
Date Acquired
August 24, 2013
Publication Date
May 27, 2009
Subject Category
Aerospace Medicine
Report/Patent Number
JSC-CN-17274
Meeting Information
Meeting: Annual Meeting of the American College of Sports Medicine
Location: Seattle, WA
Country: United States
Start Date: May 27, 2009
End Date: May 30, 2009
Sponsors: American Coll. of Sports Medicine
Distribution Limits
Public
Copyright
Public Use Permitted.
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