Optimal Training for Movement Acquisition and Transfer: Does "Externally Focused" Visual Biofeedback Promote Implicit Motor Learning?

Visual biofeedback has been shown to facilitate injury-resistant movement acquisition in adolescent athletes. Visual biofeedback is typically thought to foster implicit learning by stimulating athletes to focus attention externally (on movement outcome). However, biofeedback may also induce explicit learning if the athlete uses the visual information to consciously guide movement execution (via an internal focus). To determine the degree to which athletes reported statements indicating implicit or explicit motor learning after engaging in a visual biofeedback intervention. Prospective cohort study. Three-dimensional motion-analysis laboratory. Twenty-five adolescent female soccer athletes (age = 15.0 ± 1.5 years, height = 165.7 ± 5.9 cm, mass = 59.4 ± 10.6 kg). Standard 6-week neuromuscular training intervention (three 90-minute sessions/wk), with added visual biofeedback sessions (2 sessions/wk). For the biofeedback training, participants performed squatting and jumping movements while interacting with a visual rectangular stimulus that mapped key parameters associated with injury risk. After the last biofeedback session in each week, participants answered open-ended questions to probe learning strategies. Responses to the open-ended questions were categorized as externally focused (ie, on movement outcome, suggestive of implicit learning), internally focused (ie, on movement itself, suggestive of explicit learning), mixed focus, or other. A total of 171 open-ended responses were collected. Most of the responses that could be categorized (39.2%) were externally focused (41.8%), followed by mixed (38.8%) and internally focused (19.4%). The frequency of externally focused statements increased from week 1 (18%) to week 6 (50%). Although most statements were externally focused (suggesting implicit learning), the relatively large proportion of internal- and mixed-focus statements suggested that many athletes also engaged in explicit motor learning, especially in early practice sessions. Therefore, biofeedback may affect motor learning through a mixture of implicit and explicit learning.