Impact of back squat training intensity on strength and flexibility of hamstring muscle group

What is it about?

Flexibility is an important factor that is required for 15 the success of the athletic performance. When mus16 cular flexibility is reduced, its impacts may go be17 yond simply lessening the level of muscular func18 tionality since this reduced flexibility also leads to 19 damage of the musculoskeletal system resulting from 20 overuse [4,5]. In fact, the hamstring muscle group 21 (HMG), such as semitendinosus, semimembranosus, 22 and biceps femoris, has been shown to be the most 23 often-injured multi-joint muscle in the human body [6], 24 and it has been shown that non-injured groups tend to 25 be more flexible than the injured groups [9,10]. Flex26 ibility, or lack thereof, of the leg muscles, is also as27 sociated with low back pain [1,8,11] and HMG strain 28 injury [6,12]. For example, it was found that decreased 29 HMG flexibility in league players [13] and military 30 recruits [14] was associated with an increased inci31 dence of back and leg injuries. The muscles most likely 32 to be injured (e.g., biceps femoris) are those that are 33 used most frequently, have a high percentage of fast34 twitch muscle fibers (and so are generally involved in 35 quick, sudden movement) and are connected to mul36 tiple joints. The HMG, which fits all of the above 37 criteria, has been shown to be the most often-injured 38 multi-joint muscle in the human body [15]. In addi39 tion, a decrease in flexibility of the HMG is strongly 40 correlated to other musculoskeletal problems such as 41 chronic low back pain and HMG strains [8]. Iashvili 42 (1983) found that active ROM, not passive ROM, was 43 more correlated with sports performance. This sug44 gested that active ROM in the hip flexors and ham45 strings should be developed in a sprinter, for example, 46 to improve athletic performance (i.e., achieve full knee 47 lift and hip extension at the toe-off point of the running 48 gait to warrant an ideal stride length and running effi49 ciency) [16]. Nevertheless, the relation between perfor50 mance and flexibility (amount and degree) is not well 51 established. Therefore, more research was needed to 52 determine their relationship

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Photo by Alora Griffiths on Unsplash

Photo by Alora Griffiths on Unsplash

Why is it important?

The back squat is one of the most commonly per54 formed exercises in many resistance training pro55 grams [11]. The back squat plays an important role in 56 developing strength in knee and hip extensors and flex57 ors along with ankle plantarflexors. The HMG, which normally function as a knee flexor and co-contractor 58 during knee extension, also acts as an activator for 59 the gluteal and quadriceps muscles during the back 60 squat since the long head of the biceps femoris, semi- 61 tendinosus, and semimembranosus all cross the hip 62 joint and originate at the ischial tuberosity [10,11]. 63 While most of the available research performed on the 64 back squat describes the beneficial effects of this exer- 65 cise [17], few, if any, studies explore the possible neg- 66 ative consequences of this exercise on HMG flexibil- 67 ity. Therefore, the purpose of this study was to deter- 68 mine the effect of back squat training at two differ- 69 ent intensities on the lower-body strength and the flex- 70 ibility of the HMG, as it is difficult to isolate the ef- 71 fects of squat training on semitendinosus, semimem- 72 branosus and biceps femoris separately. It was hypoth- 73 esized that strength training would have a significant 74 negative effect on the HMG flexibility.

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