Your variable "max_sin_value_part1" is a [40x1] cell array. Each element contains a [1x1] cell array and that cell array contains a vector of doubles.
Here's an example of how to index multiples of 14 from the 6th element of your variable.
max_sin_value_part1{6}{1}(14:14:end)
I suggest you first clean up your variable to get rid of the nested cell arrays.
max_sin_value_part1b = [max_sin_value_part1{:}];
Now the variable such contains a cell array of vectors rather than a cell array of a cell array of vectors. This simplifies the example above to:
max_sin_value_part1b{6}(14:14:end)
