Jason Ng

Comparison of mechanomyographic sensors during incremental cycle ergometry for the quadriceps femoris

The purpose of this study was to examine the mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus power output relationships for the vastus lateralis and rectus femoris muscles during incremental cycle ergometry between the piezoelectric contact sensor (HP) and the accelerometer (ACC) sensor. Nine men performed an incremental cycle ergometry test to voluntary exhaustion. Polynomial regression analyses on a subject‐by‐subject basis indicated that the relationship between the normalized MMG amplitude versus normalized power output was best fit with either a linear, quadratic, or cubic model. These patterns were consistent between sensors for each muscle for each subject. No consistent relationship was found for MMG MPF within subjects and between muscle groups. In addition, there were no significant sensor × power output interactions for normalized MMG amplitude or MPF. These results suggest that, for cycle ergometry, the HP and ACC sensors provide similar information for the interpretation of motor control strategies during continuous exercise. Muscle Nerve, 2010

Hormonal and metabolic responses to a resistance exercise protocol in lean children, obese children and lean adults.

During childhood, varying exercise modalities are recommended to stimulate normal growth, development, and health. This project investigated hormonal and metabolic responses triggered by a resistance exercise protocol in lean children (age: 9.3 ± 1.4 y, body fat: 18.3 ± 4.9%), obese children (age: 9.6 ± 1.3 y, body fat: 40.3 ± 5.2%) and lean adults (age: 23.3 ± 2.4 y, body fat: 12.7 ± 2.9%). The protocol consisted of stepping onto a raised platform (height = 20% of stature) while wearing a weighted vest (resistance = 50% of lean body mass). Participants completed 6 sets of 10 repetitions per leg with a 1-min rest period between sets. Blood samples were obtained at rest preexercise, immediately postexercise and 2 times throughout the 1-hr recovery to analyze possible changes in hormones and metabolites. Children-adult differences included a larger exercise-induced norepinephrine increase in adults vs. children and a decrease in glucagon in children but not adults. Similarities between adults and children were observed for GH-IGF-1 axis responses. Metabolically, children presented with lower glycolytic and increased fat metabolism after exercise than adults did. Obesity in childhood negatively influenced GH, insulin, and glucose concentrations. While adults occasionally differed from children, amount of activated lean mass, not maturation, likely drove these dissimilarities.

Hormonal and Metabolic Responses to a Single Bout of Resistance Exercise in Prader-Willi Syndrome

Background: Prader-Willi syndrome (PWS) is characterized by excessive adiposity. Excess adiposity negatively affects hormonal and metabolic responses to aerobic exercise. This study determined whether PWS and/or adiposity affected hormonal and metabolic responses to resistance exercise. Methods: Eleven children with PWS (11.4 ± 3.1 years, 43.9 ± 7.5% body fat), 12 lean children (9.3 ± 1.4 years, 18.3 ± 4.9% body fat), and 13 obese children (9.6 ± 1.3 years, 40.3 ± 5.2% body fat) participated. The children stepped onto an elevated platform while wearing a weighted vest for 6 sets of 10 repetitions per leg (sets separated by 1 min of rest). For the children with PWS, the platform height was 23.0 cm and vest load was computed as (20% of stature × 50% of lean body mass)/23.0 cm. For the controls, the platform height was 20% of the stature and vest load 50% of the lean body mass. Blood samples were obtained before, immediately after, and during recovery from exercise (+15, +30, and +60 min). Results: All groups had similar catecholamine, insulin, and glucagon responses. The groups showed no major differences in glucose and lactate levels. The PWS children demonstrated earlier increases in fatty acids during recovery and higher glycerol and ketone levels than the controls. Conclusion: The PWS children demonstrated largely intact hormonal, glycolytic, and lipolytic responses to lower-body resistance exercise. In PWS, elevated ketone levels suggest an incomplete fat oxidation.