Hi Everyone
Thanks for your emails – this month’s question is from Richard Simmons. Richard asks “I’m looking to develop a resistance programme for a client who’s been training for about 8 months. I’ve decided to split his programme between the upper and lower body. For the quadriceps I was thinking of the leg press, knee extension and squat, what do you think?
Closed kinetic chain and open kinetic chain exercises
Let’s start by examining the importance of the exercises. The squat and leg press are classed as Closed Kinetic Chain (CKC) exercises, whereas the knee extension is considered an Open Kinetic Chain (OKC) exercise. CKC exercises are considered to be more functionally beneficial in the lower body than OKC exercises because they are closer to the actual movement patterns encountered in most sports and activities of daily living.
The difference between a CKC leg exercise to OKC ones is that the feet are fixed and do not move during the exercise. For example, during the decent phase of the squat the feet are fixed to the floor and the ankles, knees and hips flex. During the accent, the feet still remain fixed as the knees and hips extend. OKC leg exercises differ from that of CKC exercises as the feet are free to move, and the knee joint works independently of other joints. With the knee extension, the hip joint is fixed and the knee flexes and extends with the foot freely rotating.
Selecting the right exercise
Most functional activities are a combination of both CKC and OKC movements. For example, with walking 65% of the movement is weight bearing (CKC) and 35% is non-weight bearing (OKC). To increase the intensity of the activity so that the client is sprinting, the percentage changes quiet dramatically – only 5-10% of the movement is CKC whereas 90-95% is OKC. Therefore, for your programme to be balanced and effective, you should introduce a selection of both CKC and OKC exercises.
It’s important to remember that the exercises you mentioned all vary in terms of:
- hip, knee and ankle joint forces
- muscle activity
- functionality.
The squat, leg press and knee extension
During the squat and leg press, the knee and hip extend together. While the knee extends, the rectus femoris (1 of the 4 quadriceps muscles) shortens and the hamstrings (back of the thighs) lengthen – but while the hip extends, the rectus femoris lengthens and the hamstrings shorten. The result is a simultaneous concentric and eccentric contraction at the opposite ends of each muscle. This is known as the concurrent shift and is a specific neuromuscular pattern which occurs during all multi-joint leg movements. However, for OKC exercise this concurrent shift does not occur. If you only train the quadriceps (muscles on the front of the thighs) in isolation, the body will not learn the correct neuromuscular patterns involved in everyday activity. Therefore, any exercise that involves multi-joint movements should be planned into a resistance training programme.
Changing the position of the exercise
Of all 3 of the exercises, the squat is the only exercise to elicit significant hamstring co-contraction (activating the muscle). Although the leg press is a CKC exercise, it does not guarantee that substantial hamstring co-contraction will occur. However, factors that will affect hamstring co-contraction include:
- body position
- angle of force application.
For example, position the body in a fixed upright position and ensure the footplate is level with the hips. When the legs extend, the quadriceps work to extend the knee, but the hamstrings do not need work to extend the hip. This is due to the trunk being fixed when the weight is in-line with the hips. However, if we examine the lying leg-press machine, body position changes to that of the seated position. The feet are placed above the hips and the load is placed in the front. When the leg extends, the hamstrings will work to extend the hip along with the quadriceps which are working to extend the knee. So, we see that simply changing the position of an exercise can elicit a hamstring co-contraction.
Changing your body position can also change muscle activity during the squat. For example, if you position yourself with your back against a wall, you will isolate the quadriceps more. Since the torso is now more supported, the hamstrings do not need to work to keep the upright position. Other studies have shown that adopting a wide stance position for the squats will produce more hamstring and gluteal (the 3 muscles that make up the buttocks) activity, whereas a narrow stance position produces more quadriceps activity.
My advice:
Off all the exercises, I’d say the squat is the best of all the leg exercises. Numerous studies have shown that it elicits the highest quadriceps electromyographic (EMG) activity compared to the leg press and the knee extension. It’s also a CKC multi-joint exercise which elicits more co-contraction of the hamstrings.
Second to the squat is the leg press. Quadriceps activity is lower to that of the squat, but the knee compressive forces (pressure pushing on the knee) are not quite as high. The leg press is also safe from a technique point of view as the machine is easy to use. Thus the leg press can be seen as a safer and easier alternative to the squat. A disadvantage of the leg press is that it’s not necessarily functional due to the limited hamstrings co-contraction. However, if possible consider using the lying leg press if there is one available.
Of the 3 exercises, the leg extension elicits the lowest quadriceps activity. Another point to consider is that it’s an OKC single-joint movement so it will have a limited functional benefit. However, one important advantage of the knee extension is that compression forces are lower than that of CKC exercises.
Paul Miell asks: What number of ‘sets’ is suggested for a healthy adult beginner?
Numerous research papers confirm that 1 set is just as effective as multiple sets programmes. The National Strength and Conditioning Association (NSCA) has confirmed from there own research, that there are no noticeable differences between women tested for 1 set to those tested for 3.
Mia Hansel asks: What is the recommended rep range for a healthy adult beginner?
The general agreement across the board and supported by the ACSM, is that a repetition range of between 8-12 is appropriate for all client’s. For greater dynamics in repetition ranges the ACSM recommend a range between 3 and 20 that can be performed at a moderate pace.