A systematic review of sensorimotor function during adolescence: a developmental stage of increased motor awkwardness?

BACKGROUND: Although adolescent motor awkwardness and increased injury susceptibility have often been speculated and researched, studies regarding adolescent regressions in motor control have yielded inconsistent conclusions. Thus, the relationship between adolescent maturation and injury risk remains unclear. The purpose of this study was to systematically review the literature relative to two questions: (1) Which sensorimotor mechanisms are not fully mature by the time children reach adolescence? and (2) Is adolescence a period when children exhibit delays or regressions in sensorimotor mechanisms? METHODS: Systematic searches for keywords were performed in February 2010 using PubMed MEDLINE (from 1966), CINAHL (from 1982) and SPORTDiscus (from 1985) databases. Articles were reviewed relative to predetermined criteria, and the methodological quality of each included study was assessed. RESULTS: The search identified 2304 studies, of which 33 studies met the inclusion criteria. All 33 identified studies provided results associated with Question 1, 6 of which also yielded results pertaining to Question 2. The search results indicated that many aspects of sensorimotor function continue to mature throughout adolescence, and at least some children experience delays or regressions in at least some sensorimotor mechanisms. The results also exposed several significant weaknesses in our knowledge base. CONCLUSION: The identified knowledge gaps are critical barriers because they hinder methods for identifying children at high risk and diminish the efficacy of targeted prevention programmes. Implications regarding research on adolescent injury risk are discussed and recommendations for future research such as improved methodological designs and integration of non-linear analyses are provided.

Repetitive eccentric muscle contractions increase torque unsteadiness in the human triceps brachii.

Torque steadiness and low-frequency fatigue (LFF) were examined in the human triceps brachii after concentric or eccentric fatigue protocols. Healthy young males (n=17) performed either concentric or eccentric elbow extensor contractions until the eccentric maximal voluntary torque decreased to 75% of pre-fatigue for both (concentric and eccentric) protocols. The number of concentric contractions was greater than the number of eccentric contractions needed to induce the same 25% decrease in eccentric MVC torque (52.2+/-2.9 vs. 41.5+/-2.1 for the concentric and eccentric protocols, respectively, p<.01). The extent of peripheral fatigue was approximately 12% greater after the concentric compared to the eccentric protocol (twitch amplitude), whereas LFF (increase in double pulse torque/single pulse torque), was similar across protocols. Steadiness, or the ability for a subject to hold a submaximal isometric contraction, was approximately 20 % more impaired during the Ecc protocol (p=.052). Similarly, the EMG activity required to hold the torque steady was nearly 20% greater after the eccentric compared to concentric protocol. These findings support that task dependent eccentric contractions preferentially alter CNS control during a precision based steadiness task.