There is somewhere around 640 skeletal muscles in the human body.  Skeletal muscle is a complex network of muscle fibers, connective tissue, nervous tissue, and blood vessels.  The connective tissue forms a framework of support by surrounding individual muscle fibers, bundles of muscle fibers (called fascicles), and finally the individual muscles that are made up of these fascicles.  Another type of connective tissue, called fascia, plays an integral role in how muscle functions.  Deep fascia separates neighboring muscles from one another and allows for these muscles to glide smoothly past one another as they contract.  Superficial fascia separates muscle from the overlying skin, and also allows for smooth movement of contracting muscle.  Dysfunctional fascia can increase the likelihood of suffering a muscle strain.

Each muscle fiber  is composed of many sarcomeres, which are the contractile units of the muscle.  When a muscle contracts, tension is created in these sarcomeres and this tension is controlled by the Central Nervous System. Muscle strength is affected by the number of sarcomeres present in a muscle, as well as by neural recruitment of muscle cells.  Muscle length is also a byproduct of the number of sarcomeres, with an increased number of sarcomeres in alignment corresponding to increased muscle length.  Muscle strength and length imbalances can increase the likelihood of suffering a muscle strain.

Factors That Increase the Likelihood of  Suffering a Muscle Strain

A muscle strain is defined as damage to some part of the contractile unit caused by overuse (chronic injury) or overstress (acute injury).  Strains can be graded as mild, moderate, or severe.  Several factors contributing to muscle strains were mentioned under The Anatomy above.  Here is a list of the aforementioned and some additional causes:

• Dysfunctional joints above or below the injured area: if motion is limited in one area, the body will compensate and increase the demand on adjacent structures and tissues
• Dysfunctional fascia: if the fascia does not allow for smooth sliding and gliding between neighboring muscles and other structures, adhesions and scar tissue can develop
• Poor flexibility: this can be due to muscle length or fascial adhesions (scar tissue)
• Overstretching: stretching a muscle beyond its ability to recoil and return to its resting length
• Muscle strength imbalances: strength differences between muscles or muscle groups that are meant to oppose and control one another’s movement

There are other factors that can contribute to or increase the likelihood of a muscle strain, but we will focus on these five as we discuss both the rehabilitation and prevention of muscle strains.

Signs and Symptoms of a Muscle Strain

Common signs and symptoms of a muscle strain include:

• Sometimes an audible ‘POP’ is heard
• Localized pain at the site of the tear
• Stiffness
• Pain with stretching of the injured muscle
• Pain with contraction of the injured muscle
• Swelling
• Bruising

Rehabilitation Guidelines

If you have suffered a muscle strain, the general R.I.C.E. rules apply:

• Rest: take it easy
• Ice: ice no more than 15-20 minutes with at least an hour between applications
• Compression: use an ACE wrap or compression sleeve; don’t compress too tightly
• Elevation: keep the injured muscle above heart level

There are 3 phases of healing, each with different goals for rehabilitation:

Inflammatory Phase (Acute): This phase can last from 0-5 days, but generally inflammation begins to decrease after 48-72 hours post-injury.  Follow these guidelines:

• R.I.C.E.
• Range of Motion: perform gentle movements, but not to the point to pain
• Gentle stretching: not to the point of pain
• Decrease physical or recreational activity: to prevent further injury

Subacute Phase: This phase generally lasts between 5-21 days post-injury, but is variable depending on the severity of the injury.  During this phase muscle fibers are regenerating and being laid down randomly within the muscle.  It is important to gradually resume activity during this phase to help realign the new muscle fibers into an efficient position.  Follow these guildelines:

• Stretching, with increased intensity:  perform 3 sets of 30 second holds when stretching
• Massage: helps to realign new muscle fibers and free up fascial adhesions
• Gradually resume resistance training: this will also help to realign muscle fibers, as well as increase strength
• See a Physical Therapist: they can help address factors that may have contributed to the strain, such as spine mobility, pelvis mobility, inefficient muscle recruitment patterns, etc…

Maturation Phase (Recovery): This phase can last up to 6 months post-injury for the most severe cases.  This phase should consist of the following components:

• Resistance training with increase intensity: increase intensity slow and steady
• Endurance training: emphasize muscle strength and endurance
• Aerobic/Cardiovascular conditioning: don’t forget this!
• Balance and Proprioceptive training: this could be another reason why the strain occurred in the first place
• Agility training: quick movements and plyometrics.  This should be towards the end of rehabilitation

For resistance training and aerobic training guidelines, read this article!

Muscle Strain Prevention:

Based upon the predisposing factors and the rehabilitation guidelines we can formulate some key concepts to help prevent muscle strains from occurring.  Follow these five guidelines:

• Increase flexibility: Stretching all major muscle groups before and after a workout is a great idea.  Hold all stretches for 30 seconds.  Don’t stretch to the point of pain.  Beginning a Yoga program would be a great idea, but start easy and take it slow.
• Increase soft tissue mobility: This is a fancy way of saying, “get rid of the scar tissue and adhesions in and between your muscles”.  Remember the fascia that we’ve talked a little bit about?  Sometimes stretching isn’t enough.  A good physical therapist or masseuse can help you here!
• Correct strength imbalances: don’t ignore muscle groups.  For example, work your quads and your hamstrings, your triceps and your biceps, your low back and your abs, etc…  Strength imbalance not only can predispose you to a muscle strain, but possible worse!
• Work concentric and eccentric contractions: A concentric contraction means that the muscle is shortening as it is contracting.  An eccentric contraction is the opposite; the muscle lengthens as it contracts.  The easiest example to visualize this is a biceps curl.  As the weight comes up the biceps is contracting and shortening (concentric contraction).  As the weight is relaxed to its resting position, the muscle is still contracting as it is lengthening (eccentric contraction).  MOST MUSCLE STRAINS OCCUR DURING ECCENTRIC CONTRACTIONS!  You can integrate eccentric training into every exercise.  For example, when you squat, squat slowly down to your end position (controlling the eccentric contraction) and then push up.  When you bench press, lower the bar slowly (controlling the eccentric contraction) and then push up.
• See a good physical therapist, chiropractor or osteopath: they can make sure that you are moving efficiently, and eliminating extra, unnecessary demands on your muscles.

The anterior cruciate ligament (ACL) connects the femur to the tibia at the knee.  It runs from the front of the tibial plateau (top of the tibia) towards the back and inside surface of the end of the femur.  The primary role of the ACL is to prevent anterior translation of the tibia on the femur.  In other words, it prevents the lower leg from sliding too far forward compared to the upper leg.  It is also responsible for resisting hyperextension of the knee and medial (towards the inside) and lateral (towards the outside) rotation of the lower leg on the upper leg.

THE PROBLEM

According to emedicine, about 200,000 people sprain their ACL every year, and about 100,000 go on to have surgical reconstruction.  The mechanism of injury can be contact or non-contact.  Non-contact injuries are usually associated with rapid deceleration of the lower limb, knee hyperextension, or forced rotation of the lower limb.  Women are 4-6 times more likely to suffer a non-contact injury to their ACL.  A few possible explanations for this are that:

• women tend to have a wider pelvis, and therefore an increased angle at the knee (more “knock-kneed”); this places more of a demand on the hip musculature to control the leg and increases the demand on the ACL to stabilize the knee
• women tend to have strong quadriceps and weak hamstrings; this is referred to as an increased quad:hamstring ratio
• women tend to have a narrower femoral notch, which is the space at the end of the femur through which the ACL courses; this puts more physical pressure on the ACL and can wear it down
• women tend to have decreased neuromuscular control compared to men; this refers to the timing, strength, and endurance of the musculature surrounding the hip and knee

Gender aside, what can be done to prevent an ACL injury? Let’s use this information to formulate a training program that will help prevent an ACL injury in men and women.

THE SOLUTION

Emphasize the Gluts:

• The gluteus maximus is the primary muscle responsible for external rotation of the leg and the gluteus medius is the primary muscle responsible for abduction of the leg.  Simply put, these two muscles prevent the knees from coming together (knock-kneed) and rotating inward during functional activities like walking, running, jumping, etc.
• According to research, the best exercise to target the gluteus medius is side-lying leg lifts.  This is a great starting point, and can later be applied to more functional, upright positions.  TIPS! When performing side-lying leg lifts make sure that your leg is in line with your upper body or slightly behind you (extended); don’t let your hips roll backwards; keep your toes pointing up towards the ceiling
• To target the gluteus maximus, squats are a good starting point.  You can modify squats by using an exercise ball, a barbell, dumbells, wall sits, etc… BUT the best exercise to target the gluteus maximus is the single-leg squat.  That doesn’t mean you should jump right into single-leg squats though; progress slowly.  TIPS! When squatting bend at the hips, not through your low back.  Keep your knees in line with your 2nd or 3rd toe on each foot.  Don’t let your knees move forward in front of your toes (you should be able to see your toes if you look down) And don’t squat past 90°; it’ll do more damage than it’s worth.

Don’t forget the Hamstrings:

• This goes back to the quad:hamstring ratio.  When the quads contract they pull on the front of the tibia (the motion the ACL is trying to limit).  When the hamstrings contract they pull on the back of the tibia, assisting the ACL.  So it makes sense that you want to strengthen this synergistic muscle group.  The easiest way to target the hamstrings is to use a weight-machine, either in sitting or prone (on your stomach).  It is true that the hamstrings are co-contracting during squats, but they are not the primary muscle group involved; the quads are working to extend the knee, and the glut max is the primary muscle extending the hips.  TIPS! Using a fitness ball can also be a great way to workout the hamstrings.  Lie on your back and rest your heels on an appropriately sized fitness ball.  Bridge up, bringing your pelvis off of the floor.  Once stable, roll the ball towards you by bending at the knees.

Eccentric Control:

• An eccentric contraction occurs when the muscle is contracting and lengthening at the same time.  This happens all the time.  The ability to safely and efficiently perform eccentric contractions is crucial for overall control of the lower extremity (deceleration injuries!).  The best part about this is that you are already doing exercises that have an eccentric component to them (it’s everywhere).
• Try this.  Focus on the downward phase of the squat and count to 5 before reaching the bottom.  Or when performing hamstring curls on the machine, count to 5 while straightening your leg.  Or when performing side-lying leg lifts, count to 5 as you lower your leg.  This is simply emphasizing the eccentric component of the lift, which is crucial for overall stability.

First Things First:

• One of the biggest mistakes people make is progressing themselves too soon, or skipping the starting point altogether.  You have to crawl before you can walk, and you have to be able to safely perform exercises like the ones I’ve mentioned (side-lying leg lifts, squats progressing to single-leg squats, hamstring curls) before beginning a more intense program such as a plyometric program.  If your technique is faulty, you will actually be placing yourself at an increased risk for injury.
• For resistance training and aerobic training guidelines, read this article!
• If you need more help getting started, go see a physical therapist or a qualified personal trainer!