I collected muscle activity levels from 4 different leg muscles on each lower limb over a 20 jump test in 2 groups of athletes. One group has ACL injury (n=11) and there is a control group (n=11). Additionally, there are 4 separate jump phases for each individual jump. Finally, I break the 20 jumps down into 4 clusters of 5 jumps to evaluate the fatigue effects (cluster 1 = rested, cluster 4 = fatigued). You can think of the 4 clusters of jumps as a time series.
My first analysis plan was to subset my data down to each level of interest. I planned to filter out a single muscle first, and then a single jump phase. I then planned to assess equality of variance and normality and to transform my data as needed to compare the left limb to the right limb for each group separately using a paired t-test. Then, I planned to make group comparisons by comparing the injured limb of the ACL subjects to a limb average for the controls, and the uninjured limb of the ACL subjects to the limb average for the controls using a one-way anova. I would repeat this process for each muscle and each jump phase.
My second plan was to delve into something more complex like a multilevel model. Note that I would plan to build this model up to include interaction terms and the appropriate contrasts to get at my 2 primary research questions: do muscle activity levels differ between limbs and between groups w/ fatigue for ACL subjects and controls as measured over the four different jump clusters.
Here is my first attempt at this model without the interaction terms included (I wanted to save space).
Muscle.Activity.lme = lme(muscle.activity~group+limb+muscle+jump.cluster+jump.phase, random = ~1 | subject/limb/muscle/jump.cluster/jump.phase, data = EMG, method = "ML")
Is it wrong to separate out the various levels to perform between group and within group comparisons as indicated in my first analysis plan?
Is a multilevel model feasible for my data set and is this approach reasonable? I think my sample size might be too small but I'm wondering if this is a significant limitation or one that needs to be managed.
Are there any other analysis approaches that might work better?
Thank you for any insight you can provide.