Background Non-contact injuries such as anterior cruciate ligament ruptures often occur during physical load toward the end of a match. This is ascribed to emerging processes due to exercise-induced fatigue. Moreover, non-contact injuries often occur during dynamic actions such as landing or cutting movements. Inter-limb asymmetries are suggested as one possible cause for those injuries based on findings indicating that asymmetries between limbs are associated with a higher injury risk. Hence, assessing inter-limb asymmetry during physical load in the condition of exercise-induced fatigue is warranted to identify potentially relevant precursors for non-contact injuries. Objective The objective of this study was to overview the current state of evidence concerning the influence of exercise-induced fatigue on inter-limb asymmetries through a systematic review. Methods A systematic literature search was conducted using the databases Web of Science, Scopus, PubMed, SURF, and SPONET to identify studies that assessed inter-limb asymmetries of healthy people, calculated with an asymmetry equation, before and after, or during a loading protocol. Results Thirteen studies were included in the systematic review. The loading protocols involved running, race walking, jumping, squatting, soccer, rowing, and combinations of different exercises. Moreover, different tasks/procedures were used to assess inter-limb asymmetries, e.g., squats, single-leg countermovement jumps, gait analysis, or isokinetic strength testing. The results seem to depend on the implemented loading protocol, the tasks/procedures, and the measured parameters. Conclusions Future research needs more systematization and consistency, assessing the effect of exercise-induced fatigue on inter-limb asymmetries. Moreover, the emergence of inter-limb asymmetries should be regarded in the context of sport-specific movements/tasks. Testing before, after, and during a physical loading protocol is advisable to consider the influence of exercise-induced fatigue on sport-specific tasks and to identify the possible mechanisms underlying load-dependent inter-limb asymmetries with regard to risk of non-contact injury.
Dynamic postural control is challenged during many actions in sport such as when landing or cutting. A decrease of dynamic postural control is one possible risk factor for non-contact injuries. Moreover, these injuries mainly occur under loading conditions. Hence, to assess an athlete’s injury risk properly, it is essential to know how dynamic postural control is influenced by physical load. Therefore, the study’s objective was to examine the influence of maximal anaerobic load on dynamic postural control. Sixty-four sport students (32 males and 32 females, age: 24.11 ± 2.42, height: 175.53 ± 8.17 cm, weight: 67.16 ± 10.08 kg) were tested with the Y-Balance Test before and after a Wingate Anaerobic Test on a bicycle ergometer. In both legs, reach distances (anterior) and composite scores were statistically significantly reduced immediately after the loading protocol. The values almost returned to pre-load levels in about 20 min post-load. Overall, findings indicate an acute negative effect of load on dynamic postural control and a higher potential injury risk during a period of about 20 min post-load. To assess an athlete’s sports-specific injury risk, we recommend testing dynamic postural control under loaded conditions.
Inter-limb asymmetries are associated with a higher potential risk for non-contact injuries. Differences in function or performance between the limbs might lead to imbalances and promote instability, increasing the potential risk for injuries. Consequently, an investigation of inter-limb asymmetries should be included in injury risk assessment. Furthermore, since non-contact injuries mainly occur under loaded conditions, an investigation of load-induced changes of inter-limb asymmetries can provide additional information on the athlete’s potential injury risk. Therefore, the current study aimed to investigate the influence of physical load on inter-limb asymmetries in dynamic postural control, which is essential in situations with a high risk for non-contact injuries such as landing, cutting, or stopping. In total, dynamic postural control of 128 active and healthy subjects (64 males and 64 females, age: 23.64 ± 2.44, height: 176.54 ± 8.96 cm, weight: 68.85 ± 10.98 kg) was examined. Dynamic postural control was tested with the Y-Balance Test (YBT) before and after a loading protocol on a bicycle ergometer or a treadmill. The results showed no significant increase of the inter-limb asymmetries in anterior direction [F(1, 126) = 4.44, p = 0.04, η2p = 0.03]. Moreover, there is high variation between the subjects regarding the magnitude and the direction of the asymmetries and the changes due to load. Therefore, a more individual analysis considering the magnitude and the direction of the asymmetries is required. Thereby, considering different modifying factors, e.g., sex, injury history, and baseline level of asymmetries, can be helpful. Moreover, an analysis of the changes during load might provide further insights, reveal possible differences, and help detect the reasons and mechanisms underlying inter-limb asymmetries and asymmetrical loading.
Zusammenfassung Hintergrund Im Sport wird angenommen, dass ein dynamischer Knievalgus bei einbeinigen Landungen einen relevanten Verletzungsmechanismus des vorderen Kreuzbands darstellt. Während bestehende effektive Präventionsprogramme zur Reduktion des Knievalgus primär auf die Verbesserung allgemeiner konditioneller und/oder koordinativer Einflussgrößen ausgerichtet sind, fokussiert ein Video-Feedback-Training die Korrektur individueller Defizite in der sportlichen Technik, um u. a. ein potenzielles Verletzungsrisiko zu reduzieren. Ziel Evaluation der kurz- und insbesondere mittel- und langfristigen Wirksamkeit eines Video-Feedback-Trainings zur Veränderung des frontalen Kniewinkels bei einbeinigen Landungen. Methode Im Rahmen einer exploratorischen Studie wurden 10 sportlich aktive Personen (Alter: 25 ± 5 Jahre, Größe: 170,8 ± 4,5 cm) getestet. Diese führten in Anlehnung an das Landing Error Scoring System (LESS-Test) einbeinige Drop-Jumps in einem Pretest, in einer Aneignungsphase mit Video-Feedback und 2 Retentionstests 2 und 6 Wochen nach der Aneignungsphase ohne Video-Feedback aus. Das Video-Feedback wurde in der Aneignungsphase bei jedem zweiten Sprung und zusätzlich selbstbestimmt auf Nachfrage über ein Expertenmodell mit neutraler Kniestellung im Overlay-Modus aus der Frontalperspektive gegeben. Ergebnisse Die Ergebnisse wurden nach Sprung- und Nichtsprungbein der Proband*innen differenziert. Sie zeigen eine bedeutsame Verringerung des frontalen Kniewinkels für das Sprungbein (F1, 9 = 10,43, p = 0,01, η2 p = 0,54, 95 % CI [0,04; 0,74]) bei einbeinigen Landungen in der Aneignungsphase, jedoch keine statistisch bedeutsame Verringerung für das Nichtsprungbein (F1, 9 = 4,07, p = 0,08, η2 p = 0,31, 1-β = 0,44). Im Retentionstest nach 6 Wochen nähert sich der frontale Kniewinkel beidseitig dem Ausgangsniveau aus dem Pretest wieder an. Schlussfolgerung Ein Video-Feedback-Training bietet sich als einfach durchzuführendes, alternatives Verletzungspräventionsprogramm an. Eine fehlende mittel- und langfristige Veränderung und hohe Variabilität des frontalen Kniewinkels lassen eine mehrfache und/oder regelmäßige Durchführung eines Video-Feedback-Trainings sinnvoll erscheinen. In weiteren Studien mit Kontrollgruppendesign und unterschiedlichen Feedback-Prozeduren wird systematisch zu prüfen sein, ob eine längerfristige Reduktion eines potenziellen Verletzungsrisikos des vorderen Kreuzbands erreicht werden kann.
Dynamic postural control is one of the essential factors in situations where non-contact injuries mainly occur, i.e., landing, cutting, or stopping. Therefore, testing of dynamic postural control should be implemented in injury risk assessment. Moreover, non-contact injuries mainly occur under loaded conditions when the athlete is physically stressed. Therefore, risk factors and mechanisms of these injuries should also be regarded under loading conditions and not only when the athlete is recovered. Current studies examining the influence of physical load on risk factors, such as dynamic postural control, often use cycling protocols to stress the participants. Nevertheless, most types of sports require running as a central element and the induced internal load after cycling might not be the same after running. Therefore, the current study aimed to examine the influence of a running and a cycling protocol on dynamic postural control and to determine the potential injury risk under representative conditions. In total, 128 sport students (64 males and 64 females, age: 23.64 ± 2.44, height: 176.54 ± 8.96 cm, weight: 68.85 ± 10.98 kg) participated in the study. They were tested with the Y Balance Test before and after one loading protocol. A total of 64 participants completed a protocol on a cycle ergometer and the other 64 on a treadmill. A mixed ANOVA showed significant interactions of time and load type. Dynamic postural control was reduced immediately after cycling but did not change after running. These findings indicate a load type dependence of dynamic postural control that must be considered while assessing an athlete’s potential injury risk and they support the need for more representative designs.
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