THE EFFECTS OF AGING ON SKELETAL MUSCLE MORPHOLOGY AND NEUROMUSCULAR FUNCTION OF THE LEG EXTENSORS

The purpose of the present study was to examine the muscle cross-sectional area (CSA), thigh skinfold thickness (SF), maximal voluntary contraction (MVC) peak force (PF), and the log-transformed EMG and MMG amplitude (RMS)-force relationships (vastus lateralis [VL] and rectus femoris [RF]) of isometric step and ramp muscle actions of the right leg extensors for individuals between the ages of 20-75 years. In addition, myosin heavy chain (MHC) isoform content of the VL was analyzed to characterize individual fiber type composition. Fifty-seven healthy men volunteered for this investigation and were categorized into groups by age: 20-25 (n = 10; mean ± SD age = 22.3 ± 2.5 yrs; stature = 177.5 ±7.3 cm; mass = 82.0 ± 17.2 kg), 30-35 (n = 10; age = 32.3 ± 1.6 yrs; stature = 175.4 ± 6.8 cm; mass = 89.8 ± 13.4 kg), 40-45 (n = 10; age = 42.6 ± 2.3 yrs; stature = 180.0 ± 6.2 cm; mass = 86.7 ± 11.2 kg), 50-55 (n = 8; age = 52. 9 ± 1.9 yrs; stature = 174.8 ± 6.1 cm; mass = 93.6 ± 11.7 kg), 60-65 (n = 9; age = 62.8 ± 2.1 yrs; stature = 175.0 ± 6.3 cm; mass = 83.6 ± 12.1 kg), and 70-75 (n = 10; age = 73.5 ± 2.5 yrs; stature = 171.5 ± 7.2 cm; mass = 80.2 ± 12.8 kg) years of age. Thigh SF measurements were taken from the VL and the mid-thigh muscle CSA, from a peripheral quantitative computed tomography scanner, was taken at the site of MMG electrode placement. Subjects performed two MVCs, nine submaximal voluntary contractions (10, 20, 30, 40, 50, 60, 70, 80, and 90% MVC of the highest pre-testing MVC value) in random order, and two 6-s isometric ramp muscle actions from 10 to 100% of their MVC. Linear regression models were fit to the natural log-transformed EMGRMS and MMGRMS-force relationships. In addition, Bergstrom muscle biopsies were taken from the VL and were analyzed for MHC isoform content. Type I MHC isoform content was higher for the 70-75 (mean ± SD 45.8 ± 5.3%) than the 20-25 age group (37.48 ± 3.94%). For MVC PF, the 20-25 (746.2 ± 305.2 N) and the 30-35 (812.9 ± 230.7 N) age groups were higher than the 70-75 (459.7 ± 223.4 N) age group. Muscle CSA was greater for the 30-35 (190.8 ± 7.9 cm2) than the 60-65 (148.6 ± 20.4 cm2) and 70-75 (140.0 ± 22.1 cm2) age groups and, furthermore, the 40-45 (182.5 ± 43.1 cm2) age group had a greater muscle CSA than the 70-75 age group. There were no age-related differences for SF thickness and a terms from the isometric step and ramp EMGRMS and MMGRMS-force relationships. However, there were muscle-related differences for the a terms (collapsed across age groups), such as, the a terms for the VL were greater than for the RF for the isometric step and ramp EMGRMS and MMGRMS-force relationships (except for isometric ramp MMGRMS-force relationship). For the b terms from the isometric ramp MMGRMS-force relationships, there were differences between the 20-25 (0.60 ± 0.16) and 70-75 (0.32 ± 0.12) age groups, however, there were no other age-related differences for b terms from the isometric step and ramp EMGRMS and MMGRMS-force relationships. In addition, there were muscle-related differences for the b terms from the isometric step and ramp EMGRMS and MMGRMS-force relationships (except for isometric ramp MMGRMS-force relationship). For example, the b terms for the RF were higher than the VL (collapsed across age groups).The results for the present study indicated that there were no age-related changes for SF thickness and the a terms from the EMGRMS and MMGRMS-force relationships. The a terms (gain factors) have previously reflected differences in subcutaneous fat over the muscle. Therefore, since SF thicknesses were not different amongst the age groups, it is expected that there were no differences in the a terms. However, there were muscle-related differences for a terms, where the VL a terms were higher than the RF. These discrepancies between the a terms were likely the result of subcutaneous fat differences between the muscles with the VL having less subcutaneous fat than the RF. In addition, the results of the present study indicated that that there was an age-related increase in percent type I MHC isoform content with the 70-75 age group having a significantly greater amount of type I MHC isoform content than the 20-25 age group. The b terms from the log-transformed MMGRMS-force relationship from the isometric ramp contractions reflected the MHC isoform content differences between the two groups (20-25 vs. 70-75 age group) since the b terms were lower for the 70-75 age group than the 20-25 age group. There were age-related differences in MVC PF and muscle CSA that did not match the age-related differences in MHC isoform content or the b terms from the MMGRMS-force relationships. Thus, the b terms from the MMGRMS-force relationships reflected differences in motor control strategies between individuals with known type I MHC isoform content differences, but not the age-related in muscle strength or size. For EMGRMS-force relationships, there were no age-related changes for the b terms, which suggested that the EMGRMS-force relationships were unable to distinguish between different motor control strategies, between individuals with known MHC isoform content differences, or among age groups. In conclusion, the log-transformed MMGRMS-force model may be an attractive model to monitor changes in fiber type composition during the aging process when type II fibers are lost. With additional research, the log-transformed MMGRMS-force model may be a useful, noninvasive criterion for the diagnosis of sarcopenia

Methodological Differences in the Interpretation of Fatigue Data from Repeated Maximal Effort Knee Extensions

Background: Isokinetic fatigue protocols are commonly used in both research as well as in kinesiology education. However, fatigue quantification methods vary between studies. Objective: Therefore, the purpose of this study was to determine how fatigue quantification methods affect data interpretation and which methods may be most appropriate. Method: In this study, we quantified fatigue from a repeated maximal effort isokinetic knee extension test using different methods, as seen in published research. Nine healthy males and nine healthy females performed 50 concentric knee extensions at 180°•s-1. For each repetition, torque was quantified as either peak torque (PT), torque at the mid-point of the range of motion, and torque integrated over the full, middle 30° range of motion, and isokinetic range of motion. Fatigue Index was quantified using either the first and last three or five repetitions or the peak and last three or five repetitions. Torque slopes were quantified using all repetitions or repetitions that occurred at and beyond the repetition at which the greatest torque value occurred. Results: There was a significant inverse relationship between angle at PT and repetition number. Measures of fatigue were overestimated when torque integral over the isokinetic range of motion was utilized. When the first three or first five repetitions were utilized for Fatigue Index calculations, fatigue was underestimated. Conclusion: Results suggest that torque integral over the full range of motion is likely the best representation of strength or work. Also, researchers should omit the first few repetitions from their quantification of Fatigue Index or torque slope

Can Recruiting Rankings Predict the Success of NCAA Division I Football Teams? An Examination of the Relationships among Rivals and Scouts Recruiting Rankings and Jeff Sagarin End-of-Season Ratings in Collegiate Football

This is the publisher's version, also available electronically from http://www.degruyter.com.The purpose of the present study was to examine the relationships among National Collegiate Athletic Association (NCAA) Division I football teams' 2002 recruiting rankings from the Rivals (RIV) and Scouts (SCO) recruiting services and the Jeff Sagarin end-of-season performance ratings from 2002–2006. The RIV and SCO recruiting services included rankings for 100 common NCAA Division I football teams for the 2002 recruiting season. Each recruiting service included a total point system rating (TOTPTS) and average star rating (AVESTAR). The Jeff Sagarin NCAA football ratings system was chosen as an indicator of the teams' performance. Pearson product moment correlation coefficients (R) and the corresponding predictive indices (R2) were used to examine whether the 2002 RIV & SCO TOTPTS and RIV & SCO AVESTAR ratings could predict the Jeff Sagarin end-of-season ratings and total number of wins for each football team for the 2002 through 2006 seasons. In addition, R and R2 values were computed to examine whether the 2002 Jeff Sagarin end-of-season ratings and total number of wins could predict the following season's recruiting rankings (2003 RIV & SCO TOTPTS and RIV & SCO AVESTAR). The results indicated that RIV & SCO TOTPTS and AVESTAR predicted up to 45% of the variances in the end-of-season ratings and total wins. Thus, other factors (besides recruiting rankings) must be contributing to the end-of-season ratings for the 100 NCAA football teams included in this study. In addition, up to 51% of the variance in RIV & SCO AVESTAR and TOTPTS was predicted by the previous year's end-of-season ratings or total wins, which suggests that more successful seasons tend to yield better subsequent recruiting classes

Endocrine responses and acute mTOR pathway phosphorylation to resistance exercise with leucine and whey

Leucine ingestion reportedly activates the mTOR pathway in skeletal muscle, contributing to a hypertrophy response. The purpose of the study was to compare the post-resistance exercise effects of leucine and whey protein supplementation on endocrine responses and muscle mTOR pathway phosphorylation. On visit 1, subjects (X±SD; n=20; age=27.8±2.8yrs) provided baseline blood samples for analysis of cortisol, glucose and insulin; a muscle biopsy of the vastus lateralis muscle to assess mTOR signaling pathway phosphorylation; and were tested for maximum strength on the leg press and leg extension exercises. For visits 2 and 3, subjects were randomized in a double-blind crossover design to ingest either leucine and whey protein (10g+10g; supplement) or a non-caloric placebo. During these visits, 5 sets of 10 repetitions were performed on both exercises, immediately followed by ingestion of the supplement or placebo. Blood was sampled 30 min post-, and a muscle biopsy 45 min post-exercise. Western blots quantified total and phosphorylated proteins. Insulin increased (α<.05) with supplementation with no change in glucose compared to placebo. Relative phosphorylation of AKT and rpS6 were greater with leucine and whey supplementation compared to placebo. Supplementation of leucine and whey protein immediately after heavy resistance exercise increases anabolic signaling in human skeletal muscle

Can Recruiting Rankings Predict the Success of NCAA Division I Football Teams? An Examination of the Relationships among Rivals and Scouts Recruiting Rankings and Jeff Sagarin End-of-Season Ratings in Collegiate Football

The purpose of the present study was to examine the relationships among National Collegiate Athletic Association (NCAA) Division I football teams' 2002 recruiting rankings from the Rivals (RIV) and Scouts (SCO) recruiting services and the Jeff Sagarin end-of-season performance ratings from 20022006. The RIV and SCO recruiting services included rankings for 100 common NCAA Division I football teams for the 2002 recruiting season. Each recruiting service included a total point system rating (TOTPTS) and average star rating (AVESTAR). The Jeff Sagarin NCAA football ratings system was chosen as an indicator of the teams' performance. Pearson product moment correlation coefficients (R) and the corresponding predictive indices (R2) were used to examine whether the 2002 RIV & SCO TOTPTS and RIV & SCO AVESTAR ratings could predict the Jeff Sagarin end-of-season ratings and total number of wins for each football team for the 2002 through 2006 seasons. In addition, R and R2 values were computed to examine whether the 2002 Jeff Sagarin end-of-season ratings and total number of wins could predict the following season's recruiting rankings (2003 RIV & SCO TOTPTS and RIV & SCO AVESTAR). The results indicated that RIV & SCO TOTPTS and AVESTAR predicted up to 45% of the variances in the end-of-season ratings and total wins. Thus, other factors (besides recruiting rankings) must be contributing to the end-of-season ratings for the 100 NCAA football teams included in this study. In addition, up to 51% of the variance in RIV & SCO AVESTAR and TOTPTS was predicted by the previous year's end-of-season ratings or total wins, which suggests that more successful seasons tend to yield better subsequent recruiting classes.