Merge pull request #1031 from amtriathlon/master

Fixes translation error found by spanish users
Science Doc Updates

.. remove references to aerobic and anaerobic threshold as they
   are not really used in the literature anymore

.. remove talk of training interventions and just point out that
   power at LT2 (CP/FTP) is a good indicator of endurance performance

.. we should add a section on MU recruitment and fatigue and
   training interventions with the new features in v3.2
Spanish translation fixes contributed by Omar Torres (omar.torres@gmail.com)