Activations and Structures of the Lower Extremity Muscles: Implications for lower extremity injuries in sports

Abstract

This thesis mainly focuses on activations and structures of the lower extremity muscles and implications for lower extremity injuries in sports with exploring key aspects of muscle functionality and injury prevention, with a primary focus on the gastrocnemius and hamstring muscles. Through a series of studies, it evaluates specific exercises, training programs, and injury risk factors to provide evidence-based recommendations for athletes across various sports disciplines. Chapter Two is an investigation of the electromyographic (EMG) activity of the medial and lateral gastrocnemius muscles during eccentric heel-drop exercises (HDE) performed in various hip rotation positions, with and without external weights. Findings indicate that HDE performed in hip-internal rotation achieves high activation levels in the medial gastrocnemius without the need for additional equipment. Findings of the Chapter Two suggests that HDE can be a practical and effective preventive exercise for athletes in sports prone to calf muscle strains, such as tennis and football, emphasizing its applicability in athletic training regimens. Chapter Three is a systematic review and meta-analysis of randomized controlled trials (RCTs) which assesses the effects of exercise interventions on lower extremity muscle stiffness. The analysis reveals that static stretching and drop-jump training significantly reduce stiffness in key muscles such as the medial gastrocnemius and biceps femoris. However, the limited number of RCTs necessitates cautious interpretation. The study underscores the potential of specific training programs to mitigate muscle stiffness and highlights the need for further research to establish more definitive conclusions. Chapter Four is a retrospective study of the relationship between anterior cruciate ligament (ACL) reconstruction history and passive hamstring muscle stiffness, a known risk factor for hamstring strain injuries (HSI). Using ultrasound-based shear-wave elastography, no significant differences in passive muscle stiffness were detected between athletes with and without a history of ACL reconstruction. This finding suggests that other muscle regions or structural factors may play a more critical role in post-ACL reconstruction changes. The chapter calls for future studies to assess hamstring stiffness across broader regions to better understand structural adaptations following ACL injuries. Moreover, Chapter Four suggest that applying the same retrospective study on female athletes may present valuable data as female athletes tend to have more ACL injuries than male athletes. Chapter Five of this thesis evaluates the impact of age and fatigue on eccentric hamstring strength and muscle soreness in professional soccer players. Results show that older players (23+ year-old) experience significant reductions in eccentric hamstring strength after match play, with age being a significant predictor of strength decrements. Both younger (19–22-year-old) and older players reported increased muscle soreness post-match, though younger players perceive higher soreness levels. These findings highlight the importance of targeted interventions to address eccentric strength deficits in older players and to monitor recovery, reducing injury risk during subsequent matches.

Overall, this thesis provides valuable insights into muscle functionality, injury risk factors, and preventive strategies for the gastrocnemius and hamstring muscles. The findings emphasize the need for tailored training programs and recovery monitoring, particularly in populations at greater risk of muscle injuries, such as older athletes or those with prior ACL injuries.

Date of Award	27 Jun 2025
Original language	English
Awarding Institution	Bangor University
Sponsors	The Ministry of National Education of the Republic of Türkiye
Supervisor	Vicky Gottwald (Supervisor) & Julian Owen (Supervisor)