Date of Award
Ph.D. in Health and Kinesiology
Health, Exercise Science, and Recreation Management
Jeremy P. Loenneke
John P. Bentley
Millions of dollars are spent analyzing inter-individual differences in response to resistance exercise, but the lack of a non-exercise control group means they may simply be examining random error. The purpose of this study was to determine whether there are inter-individual differences in response to two distinct resistance exercise protocols. Participants (n=151) were randomly assigned to one of 3 groups as follows: (1) a traditional exercise group performing 4 sets to failure with a load that could be lifted 8-12 times; (2) a one-repetition maximum (1RM) training group performing a 1RM test each visit; and (3) a non-exercise control group. Both exercise groups performed 18 sessions of elbow flexion exercise over 6 weeks. Both 1RM training (2.3kg) and traditional training (2.4kg) increased 1RM strength to a similar extent. Only the 1RM group increased untrained arm 1RM strength (1.5kg) which was greater than both other groups (p<0.05). The traditional exercise group also increased ultrasound measured muscle size at all sites (all>0.22cm), each of which were greater than both the control and 1RM group (p<0.05). The 1RM group did not increase muscle mass (p>0.05). Across both training groups, the only individual responses were found in the change in 1RM strength of the trained arm in the traditional training group (Levene’s test p<0.05) in which 10 individuals (25%) were classified as responding differently from the mean. The variability in the response to other outcomes did not exceed that of the control group indicating it could not be detected above random error. Other commonly used approaches of classifying differential responders such as clustering analyses, standard deviations above and below the mean, and upper/lower percentiles would produce different results but are not appropriate. These findings demonstrate the importance oftaking into consideration the magnitude of random error when classifying individual responders, and provide possible rationale as to why numerous analyses fail to find/replicate what genes may be responsible for producing more favorable exercise outcomes.
Dankel, Scott J., "Do Individual Responses to Resistance Exercise Exist to an Extent That Can be Detected Beyond That of Measurement Error/Random Biological Variability?" (2019). Electronic Theses and Dissertations. 1568.