fitness=read.table("fitnessdata.txt",header=T,sep="")

attach(fitness)

# the paired t-test uses the same command with different options
# as usual, the default is a 2-tailed test

t.test(after,before,paired=T)

# or you can calculate the differences and then do a 1 sample t-test
d=after-before
t.test(d,mu=0)