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Monitoring acute effects on athletic performance with mixed linear modeling . UNLABELLED There is a need for a sophisticated approach to track athletic performance and to quantify factors affecting it in practical settings . PURPOSE To demonstrate the application of mixed linear modeling for monitoring athletic performance . METHODS Elite sprint and middle-distance swimmers ( three females and six males ; aged 21-26 yr ) performed 6-13 time trials in training and competition in the 9 wk before and including Olympic-qualifying trials , all in their specialty event . We included a double-blind , randomized , diet-controlled crossover intervention , in which the swimmers consumed caffeine ( 5 mg x kg ( -1 ) body mass ) or placebo . The swimmers also knowingly consumed varying doses of caffeine in some time trials . We used mixed linear modeling of log-transformed swim time to quantify effects on performance in training versus competition , in morning versus evening swims , and with use of caffeine . Predictor variables were coded as 0 or 1 to represent absence or presence , respectively , of each condition and were included as fixed effects . The date of each performance test was included as a continuous linear fixed effect and interacted with the random effect for the athlete to represent individual differences in linear trends in performance . RESULTS Most effects were clear , owing to the high reliability of performance times in training and competition ( typical errors of 0.9 % and 0.8 % , respectively ) . Performance time improved linearly by 0.8 % per 4 wk . The swimmers performed substantially better in evenings versus mornings and in competition versus training . A 100-mg dose of caffeine enhanced performance in training and competition by approximately 1.3 % . There were substantial but unclear individual responses to training and caffeine ( SD of 0.3 % and 0.8 % , respectively ) . CONCLUSIONS Mixed linear modeling can be applied successfully to monitor factors affecting performance in a squad of elite athletes .
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Intervention_Educational
diet-controlled crossover intervention
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Intervention_Pharmacological
caffeine
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Intervention_Control
placebo
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Intervention_Pharmacological
caffeine
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Outcome_Other
effects on performance
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Outcome_Other
effects
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Outcome_Other
performance times in training and competition
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Outcome_Other
Performance time
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Outcome_Other
performed substantially better
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Outcome_Other
performance in training and competition
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Participant_Sample-size
three
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Participant_Sex
females
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Participant_Sample-size
six
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Participant_Sex
males
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Participant_Age
aged 21-26