Effects of Fatigue From Resistance Training on Barbell Back Squat Biomechanics

Abstract

Exhaustive resistance training programs that have been previously referred to as extreme conditioning protocols have increased in popularity in military and civilian populations in recent years. However, because of their highly fatiguing nature, proprioception is likely altered during such programs that would significantly affect the safety and efficacy of such programs. Therefore, the purpose of this study was to assess the alterations in movement patterns that result from extreme conditioning protocols and to evaluate if these protocols can be deemed safe and effective. Twelve men (age 24 ± 4.2 years, height 173.1 ± 3.6 cm, weight 76.9 ± 7.8 kg, body fat percentage 9.0 ± 2.2%) and 13 women (age 24.5 ± 3.8 years, height 166.9 ± 8.5 cm, weight 66.1 ± 9.2 kg, body fat percentage 18.6 ± 4.0%) with at least 6 months of resistance training experience involving barbell bench press, barbell deadlift, and barbell back squat performed a highly fatiguing resistance training workout. During the barbell back squat, a 2-dimensional analysis was performed where the knee and hip angles were recorded throughout the 55 repetitions of the workout. At the early stages of the protocol, knee angle was significantly lower in men and in women demonstrating less knee flexion. Also, hip angle was significantly lower early in the program in men and in women, demonstrating a greater forward lean. The technique changes that occur in high repetition sets do not favor optimal strength development and may increase the risk of injury, clearly questioning the safety and efficacy of such resistance training programming. This is likely a display of self-preservation by individuals who are faced with high repetition programs.

Kinetic and Kinematic Changes during a 30-Repetition Bout of the Barbell Clean

“…The authors reported changes in squat technique and suggested there was evidence of increased likelihood of injury as fatigue developed. In particular, the authors measured reduced movement at the knee joint (abbreviated squat depth) and determined that injury risk was increased due to greater forward lean of the trunk [2]. However, counter-intuitively, the results showed that squat depth increased and the amount of forward lean decreased across the repetitions as fatigue developed.…”

“…However, counter-intuitively, the results showed that squat depth increased and the amount of forward lean decreased across the repetitions as fatigue developed. The authors interpreted these results as evidence of participants adopting a self-preservation behavior at the beginning of the highly fatiguing task and that when they were confident in their ability to complete the protocol the participants adopted more appropriate and effective movement patterns [2].…”

“…Training programs characterized by the use of compound resistance exercises combined with high-volumes, moderate to high loads and short rest periods have become popular in both military and civilian populations [1,2]. Such programs are commonly referred to as extreme conditioning programs [1] and exercise professionals have predicted that participation in these activities will continue to increase in the near future [3].…”

“…Such programs are commonly referred to as extreme conditioning programs [1] and exercise professionals have predicted that participation in these activities will continue to increase in the near future [3]. However, a number of researchers have raised concerns regarding the safety of combing technically demanding ballistic resistance exercises with high-repetitions over short time periods [1,2]. In particular, it has been asserted that for ballistic exercises such as the barbell clean, fatigue accrued from performing high-repetitions can readily prompt unsafe movement execution and lead to acute injury [1].…”

“…Recently, Hooper et al [2] performed a two dimensional biomechanical analysis of a fatiguing resistance training program comprising performance of the back squat, bench press and deadlift, each with 75% 1RM. The participants rotated around each exercise in a circuit, beginning with ten repetitions in a set and reducing the number performed consecutively by one until they reached the final set comprising a single repetition (i.e., fifty five repetitions were performed for each exercise).…”