Hamstring Training: Knee Flexion

Today’s instalment is about getting the most from knee flexion exercises. The standard ‘3 sets of 10’ on the leg curl machine just won’t cut it anymore…

Go Heavy, Train With Density

Hamstrings are fast twitch. Knee flexion is as close to hamstrings isolation as you’ll get. Put them together and you’ll probably realise it’s a good idea to train them heavy. Reps in the region of 4-6 should be the norm, not the exception. Get the density up too – hamstrings love this. 10 total sets of hamstrings in a workout is good benchmark, get 6 of these from knee flexion exercises.

Fixed Lower-Limb, Moving Body

Examples (see videos): Glute Ham Raise, Nordics, Inverse Curl

Exercises that force you to move your bodyweight through space are the better choice for most people in the majority of circumstances. Think pull ups vs. pulldowns or squats vs. leg press. These exercises require additional stability and therefore the co-contraction of many different muscle groups. All of the above examples require strong gluteal and abdominal contraction to maintain a neutral spine.


Fixed Body, Moving Lower-Limb

Examples: Seated Leg Curl, Prone Leg Curl, Standing Leg Curl

Bodybuilders love these for a reason. By making the movement more stable we can focus more of our attention on the hamstrings. This is a good move if we’re looking for hamstring hypertrophy or to emphasise medial/lateral musculature (see below). Given that many gyms will have a range of leg curl machines, it’s typically easier to get variation in these types of movement.

Get The Rep Right

  • Don’t skimp on the range. Get the ankles as close the bum as possible – or vice versa depending on the exercise. Full ROM = more work = more muscle fibres.
  • Hold the top, contracted position for at least a count of one. Most individuals are weak in this position so make sure you train here.
  • Lower under complete control and over a period of at least 3 seconds. The eccentric phase is crucial for adaptation (see below).
  • Get a full stretch during the eccentric phase. This isn’t only for recruiting more muscle fibres, most individuals are prone to tightness in the hamstrings. Performing resistance exercise through a full ROM will increase and maintain flexibility.
  • Actively contract the quads in the bottom position. This reciprocally inhibits the hamstrings, facilitates a greater stretch and increases motor unit recruitment in their subsequent concentric contraction.
  • Get your core on. The tendency is to hyperextend the lower back to complete the movement, particularly when lifting heavy. With fixed lower-limb exercises always prefix the movement by getting the abs and glutes tight first – be strict. With fixed body exercises just focus on the abs. Now, a little extension is permissible during leg curls – just don’t overdo it.

Train With Eccentrics

As discussed in part one, sport and exercise places significant eccentric stress on the hamstrings. Inadequate eccentric strength of the hamstrings is a big risk factor for both hamstring and knee injuries so it makes sense to address this. It’s not just for athletes though, everyone can benefit from eccentric training. Far greater forces can be applied during eccentrics; this increases the amount of micro-damage within the muscle and the potential for adaptation. Hamstrings respond particularly well to eccentric training due to their fast twitch make up.

Implementing Eccentric Training

It doesn’t have to be eccentric-only training, providing an eccentric overload to your regular exercises can reap similar benefits. There are two main ways to implement this: a) increase duration of the eccentric phase (more than 3 seconds) and/or b) increase relative load during the eccentric phase. A great method for the latter would be the 2 up, 1 down leg curl – perform the concentric phase with both legs, as normal, then lower the weight with just one.

To Point Or Not To Point

The gastrocnemius muscle of the calf is, much like the hamstring musculature, bi-articular. It not only plantar-flexes the ankle joint but also assists in knee flexion. The fibres of the muscle aren’t long enough to do both at the same, a concept called active insufficiency. If we plantar-flex the ankle during knee flexion we reduce the contribution of the gastrocnemius and force the hamstrings to work harder. I now tend to coach dorsi-flexion on the concentric phase and plantar-flexion on the eccentric phase. This allows greater weights to be used than would be possible if plantar-flexing throughout the whole movement and overloads the eccentric phase of the movement.


Rotate The Feet

Part one of the series highlighted that the medial hamstrings (semimembranosus and semitendinosus) internally rotate the tibia and the lateral hamstrings (biceps femoris) externally rotate the tibia. Rotating the foot inwards (toes towards one another) during knee flexion will emphasise the medial hamstrings, rotating them outwards (toes away from one another) will emphasise the lateral hamstrings. By altering the position of the feet during knee flexion exercises we can hit a greater number of muscle fibres than would otherwise be possible. More muscles fibres innervated = greater potential for hypertrophy.

Address Imbalances

Imbalances stall potential gains and increase the risk of injury; ignore them at your peril. Using the above information we can determine where weaknesses and imbalances lie. To work out where to focus your individual attentions, just take note of what your feet do when you start to fatigue during an exercise. If the feet turn outwards then focus on the medial hamstrings, if they turn inwards then focus on the lateral hamstrings. Needless to say, keep the left and right side in balance too.

Switch Off The Knee Extensors

Muscles like to work in antagonistic pairs; when one is firing the other should relax. The hip extensors are prone to overuse and carry the tendency to become overactive. If they are unable to ‘switch off’ this impairs contraction of the knee flexors. Foam rolling and stretching the hip extensors will help them relax and allow the hamstrings to produce a stronger contraction.

Body Position, The Underused Variable

Variation of rep ranges, exercises, etc. is great, but there’s one variable we tend to overlook. Altering the body position will change the point of the strength curve which is overloaded, helping to ensure the most complete hamstring development. Using different machines will do this naturally but you can adapt in other ways too. For example, alter the amount of hip flexion, such as during the ‘razor curl’, or the angle of the body, such as Nordics from a decline sit-up board.


Knee flexion = done. Hip extension = … well, you’ll have to wait until next time!

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