The studies findings indicated that the FRT showed no significant relationship to strength gains and that work capacity (reps x weight during second phase of FRT) showed only a modest (r=0.58-0.59) relationship. Considering the authors own comments in the full text on the disadvantage of work capacity as strength indicator (both variables involved are equally weighted but can fluctuate to varying degrees over time), I am lead to think that this is likely little more useful in prediction than the FRT.
Now what I have found most interesting with regard to this paper comes from their initial hypothesis. Their data causes me question another similar hypothesis, that although widely spoke of within the Resistance training community and not without theoretical basis or anecdotal support, has no empirical studies in support of it.
The authors hypothesis was as follows from the full text:
"We hypothesised that subjects with low levels of fatigue would show a trend towards larger training progression than subjects with high levels of fatigue, as they were expected to be loaded more appropriate to their physiological training potential."
Certainly within the HIT community there are varying opinions upon different time under load (TUL), number of reps, or however people may be recording their progress. Some suggest that a particular TUL or rep-range may be better suited to a particular phenotype. When discussing genetics within Body By Science the idea is touched upon, however the evidence is very theoretical.
The training protocol the study utilised was aimed at being 'endurance' based involving a higher number of repetitions. (We'll forget the erroneous premise that endurance and strength gains are independent for now.) By showing no predictive value using their regression models the study essentially showed that participants with a lower fatigue rate in the FRT (potentially those with more slow twitch fibres) do not get any greater gains in strength when using a protocol more 'suited' to their phenotype.
There were no comparisons made to see if this were the case for those who were potentially more 'fast twitch' so we can't say for certain that the idea of physiologically suited training protocols can be entirely ruled out as bunk. But this study certainly doesn't help support the idea either.
In light of this a basic study and test of the hypothesis would ideally involve a design using two groups homogeneous of phenotypes i.e. half fast, half slow twitch (Ok we could go into more detail with this but you get the idea). Both groups train using a protocol involving training to momentary muscular failure with one variation between groups. One group trains using a high weight with low reps/TUL, the other trains using low weight high reps/TUL and we compare the subgroups in pre and post strength/hypertrophy. Simple.
Without any conclusive evidence I must say I have to agree with the conclusion from Carpinelli's article on the Size Principle :
"Very high RMs (e.g., loads lighter than 20 RM) or an extensive time under load (e.g., longer than 2–3 minutes) may involve mechanisms of fatigue that are not conducive to stimulate optimal increases in muscular strength. Despite the plethora of opinions in the resistance training literature, the specific mechanisms of fatigue and exactly what constitutes an optimal stimulus for strength gains are unknown. If a maximal—or near maximal—effort is applied at the end of a set of repetitions, the evidence strongly suggests that the different external forces produced with different amounts of resistance elicit similar outcomes."