Twenty-six experienced golfers, randomised to four weeks of synchronised metronome training or to a group that just practised. The training group became significantly more accurate and less variable. That result is real and it is encouraging.
It is also about 13 people per group, with no sham or attention-matched control, no blinding, on a simulator rather than a course, from a single laboratory — and it has never been independently replicated. The intervention is a commercial product and the paper is distributed by its manufacturer. A follow-up on swing kinematics had no control group at all. We cite it; we don’t lean on it.
Sommer & Rönnqvist, J. Sports Science & Medicine 8 (2009), 648–656. Sommer, Häger & Rönnqvist, Sports Biomechanics 13 (2014). Kim & Ridgel, IJSSC 14 (2019).