By Ricky Siebeler
Yet another entry on how to properly train a certain muscle. Often neglected, the hamstrings require some special attention when it comes to training. Being one of the main contributors to all lower body movements, the hamstrings need to be properly developed for longevity (functional and injury free). This article will discuss all the important aspects about training of the hamstrings. It should be mentioned though that this article will mostly focus on training concepts, instead of the training itself. This makes the article a little less straightforward, and perhaps a bit more difficult. The understanding of these concepts will clarify a lot about why and how you should train certain muscles, not just the hamstrings. The main concepts being discussed in this article will be: anatomy, injury prevention and training.
The word “hamstring” functions as a generic term referring to any of the three posterior thigh muscles. The posteriors thigh’s musculature is made up out of three muscles: the Semitendinosus, Semimembranosus and Biceps Femoris (which consists of a long & short head). The hamstrings (except for the Bicep Femoris short head) are biarticular muscles, which means it crosses two joints . This enables the muscles to initiate movement at both joints. The Semitendinosus, Semimembranosus and Biceps Femoris long head originate from the Ischial Tuberosity and mainly attach to medial (towards the midline of the body) surface of the Tibia, medial Tibial Condyle and head of the Fibula, respectively . The Bicep Femoris short head originates from the Linea Aspera and Lateral Supracondylar line of Femur, and attaches to the head of the Fibula. A more basic explanation would be that they originate from the pelvis and upper Femur, and attach to the lower leg bones.
All of the hamstring muscles contribute to flexion of the knee . Besides flexion, the hamstring muscles contribute greatly to hip extension . Important to note though, is that because of the way the Bicep Femoris short head attaches to the Femur (and not the pelvis), the short head does not contribute to hip extension . Besides these two most commonly known functions, the hamstrings also contribute to knee rotation: the Semitendinosus and the Semimembranosus for internal rotation (inward), and the Bicep Femoris for external rotation (outward). Whilst not being a hamstring, the Gastrocnemius (a calve muscle) also contributes to knee flexion. This has implications for training, which will be discussed later.
Being a biarticular muscle comes with some disadvantages: it’s not possible to fully flex (bend) the knee during hip extension or extend the knee during hip flexion, because a muscle can only shorten (this is what happens during contraction) a certain amount, this is called active insufficiency. The opposite, passive insufficiency, means that it is not possible to fully extend the knee with flexed hips.
Fun Fact: there is a popular belief that the hamstring muscles are a fast-twitch muscle group, meaning it may be beneficial to train them in the lower rep-ranges. In fact they are more balanced, with slightly more slow twitch muscle fibers. Being a balanced muscle group, it would be beneficial to train in a high variety of rep ranges . It should be noted that beneficial effects of fiber-type specific training have proven not to be significant .
Hamstring Injury Prevention
Most hamstring or hamstring related injuries occur during the shift from eccentric to concentric, especially when the hamstrings are at near full length . A common scenario where this might happen are during eccentric loaded exercises such as Romanian deadlifts (especially near the bottom part of the motion). Hamstring injuries are common in running sports, they often occur during a sprint when you push off with your back leg while in hip flexion. The hamstrings experience relatively high peak forces during these movements, and are thereby more prone to injury . Hamstring injuries often occur at the insertion point (such as the Pelvis), muscle belly (anywhere but insertion point, for example at the peak of your Bicep Femoris ) injuries typically only happen during direct trauma (being hit by a car, dropping the barbell during a benchpress). There are numerous factors concerning injury prevention, this article will cover the most common ones.
First up is flexibility. As mentioned before hamstring injuries often occur when the hamstring reaches near full length. By working on your flexibility you can minimize these injuries . Unfortunately there are not that many prospective studies on flexibility in athletes participating in strength training, but there are studies showing significant injury-rate reductions in soccer-players and endurance athletes when performing several stretches . Considering the fact that hamstring injuries often occur in the same circumstances (peak force in near full length), these studies translate fairly well to strength athletes.
A good warm-up offers multiple benefits, some of which are crucial for injury prevention. Preconditioned (warmed up) muscles are able to handle more force before failing and an additional amount of lengthening . It should be mentioned that just stretching is not a complete warm-up, contradictory to what some people think. A good warm-up should always include some dynamic movements.
The effect of fatigue on hamstring injury prevalence has not been studied in athletes performing strength training. However, it is known that a fatigued muscle is able to absorb less force per lengthening unit . Explanation: a muscle can absorb a certain amount of force for every inch it stretches. When a muscle is fatigued this amount decreases. This leaves the force absorbance balance positive (the muscle absorbed more force than it can compensate), which has to be compensated for to prevent unnecessary stress on the joints. The muscle does this by stretching out further (putting the muscle in a more injury prone position). Meaning that it would not be wise to perform a relatively injury sensitive exercise, after the completion of a long and tiring hamstring workout.
Previous hamstring injuries may cause some scarring and fibrosis (excess fibrous connective tissue), which slightly decreases the hamstrings capability to lengthen, creating a more injury prone hamstring [15-17].
This article is not meant to be a form rant, so the importance of form will only be discussed by an example. Consider performing a squat with goodmorning-form during the concentric phase. This stretches the hamstring muscles to near full length, while lifting a supra-maximal weight for a goodmorning. This shows the importance of form when it comes to injury prevention.
Muscles can be trained in multiple ways, the three most common being: concentric (shortening of the muscle), eccentric (lengthening of the muscle) and isometric (muscle remaining at the same length). During strength training the main focus will be on both concentric and eccentric. In order to effectively train the hamstring muscle one should make sure both of these contractions occur . Considering the functions of the hamstring muscles (knee flexion, hip extension, knee rotation), squats and deadlifts can be rendered sub-optimal exercises for the hamstring muscles. During both of these exercises the hips and knees either extend or flex at the same time. By lengthening one side and shortening on the other the muscle remains about the same length. In order to build some strong/big/healthy hamstrings, one should include exercises that specifically target the hamstring muscles, instead of just squats and deadlifts.
Hip extension exercises activate the proximal (close to the origin of the body part) part of hamstring muscles to a greater extend compared to knee flexion exercises . Considering the majority of the proximal hamstring is made up of the Semitendinosus, it may be worth training hip extension to minimize the risk of a Semitendinosus injury. In order to even further increase the Semitendinosus activation it may be wise to slightly internally rotate the feet , the hamstrings are affected by knee rotation as you may remember from the anatomy part. The most common hip extension exercises used for hamstring training are the Romanian Deadlift (RDL), Stiff Legged Deadlift (SLDL) and the Good Morning (GM). The RDL and GM allow for constant tension throughout the movement. The SLDL has a deadstop in the stretched position, this makes the SLDL an inferior exercise for targeting the hamstrings. This sudden shift in tension, during the SLDL, renders the hamstrings more prone to injury. The constant tension during the RDL and GM allows for better cues to determine when the muscle is near fully stretched and when to stop, because of this injury prone position. Whether one of these two exercises is superior to the other remains to be studied, however the RDL does show a significant higher hamstring activation during an EMG-study .
Besides hip extension exercises, a training program should also include knee flexion exercises. Like mentioned before in the anatomy part of this article, the Bicep Femoris short head only contributes to knee flexion, as it does not attach to the pelvis. During knee flexion the entire distal part is activated to a greater extent than during hip extension . When it comes to knee flexion exercise selection there are several options, each of them with their own benefits. An EMG-study concluded that out of all knee flexion exercises the highest hamstring activation occurs during the glute-ham raise (which is also a hip extension exercise) , as well as being a closed-chain movement. A similar activation is found in hamstring exercises that are alike, such as the Nordic Hamstring Curl .
There is also one of the more obvious knee flexion exercises available: the leg curl. As mentioned in the anatomy part of the article, the Gastrocnemius contributes to knee flexion. The leg curl enables us to take the Gastrocnemius out of the movement. When the ankle joint is in plantar flexion, the Gastrocnemius no longer contributes to the movement (because of active insufficiency), so it isolates the hamstrings. The Gastrocnemius can also be used to overload the eccentric part of the movement, simply by performing the concentric part of the movement while in dorsiflexion and the eccentric in plantarflexion. In order to target the Bicep Femoris more effectively it can also be more efficient to externally rotate the feet . The next decision is whether to use the lying or seated leg curl, extended/flexed hips being the main difference. Considering hamstring injuries happen more often during the eccentric stretch, the focus should be on training the strengthening of this portion of the movement. Recent research suggests that increases in eccentric strength are larger when training the muscles at longer lengths , suggesting the seated leg curl is superior to the lying leg curl, because the hamstrings are more lengthened when in hip flexion. This study also suggests that training the muscle when stretched (injury prone) is an effective way to strengthen that part of the movement, which would be great for injury prevention.
In the near future we will be writing quite a few articles concerning all previously mentioned concepts, but from a more practical standpoint. These practical articles will require theoretical knowledge about some of the concepts mentioned in this article, in order to fully understand them.
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