In-Season Strength Training Defense By Beth Byron, MS, CSCS

Do you not believe in strength training for your athletes? Do you think it won’t really have an affect? You think it will be detrimental to their performance? Do you think it’s good to do in the off season but not really during the season of training and competition? Do you just not have enough background information to make a sound decision on all of this? Confused??? Well here is a short and sweet summary of information supported through scientific research that will answer those questions…….

The purpose of this review of literature is to provide you with informative and practical research regarding the effects of concurrent resistance training and sports specific soccer endurance training on endurance sport performance by measuring the following physiological variables: muscular strength, power, cross sectional area, maximal oxygen consumption, mitochondrial and capillary density, and body mass. Keep in mind that different training environments and test protocols have an effect on the agreement of some of the results produced through the different research studies.

First we will investigate the results of participating in only a resistance training program 3-4 days per week over an 8-12 week period. Secondly, you will see the results presented on the effects of participating only in endurance training on a consistent daily basis for 8-12 weeks. Physiologically this is very similar to participating in only soccer specific training (long sprints or shuttles, agilities, hours of practice and skill work on the field). Finally, we will see the results of what happens when the 2 types of training are combined together, also referred to as concurrent training.

Affects of Resistance Training

The common findings in the research suggested that resistance trained-only subjects

1. Increased cross sectional area of all muscle fiber types

2. Increased glycogen content

3. Increased muscle force production and strength

4. Increased muscle protein content

5. Increased anaerobic power

6. Increased ratio of type IIa to type IIb fibers (IIb have more oxidative properties than IIa which have more anaerobic properties)

7. Increase in short term power output (Wingate test)

8. Increased time to exhaustion

9. Decreased mitochondrial density

10. No significant changes in VO2 max

11. Increased body weight and lean body mass

12. Increase in peak torque in both knee flexion and extension

13. Increased vertical jump height and power

Basically what this translates to in laymen terms is:

1. Muscle fibers got bigger.

2. Greater amounts of stored muscle fuel (glycogen).

3. Muscles were able to generate more force and at a faster rate.

4. Greater amounts of protein necessary to build new and repair damaged muscle tissue.

5. You will be more powerful during short bursts of activity (running, jumping, etc.).

6. Your muscles will be more efficient in performing more high power explosive activities than longer duration, moderate intensity activities.

7. Same as #5, but this was measured specifically on a stationary bike.

8. You can work for a longer period of time before you get tired and have to stop.

9. The number of muscle cells that use oxygen to fuel the muscles stayed the same, but the muscles fibers got bigger, so there is less oxygen utilization available.

10. There were no changes in the ability to take in and use as much oxygen as possible.

11. You weigh more because you have more lean muscle mass.

12. Your leg produces more force and speed around the knee allowing you to run faster and decelerate/stop better.

13. You can jump higher; and since you weigh more due to your increased muscle mass you are actually more powerful.

Affects of Endurance Training

Common findings of endurance trained-only subjects suggested that:

1. Decreased muscle fiber diameter

2. Increase in capillary density

3. Increased mitochondrial density

4. Increased intramuscular substrate stores

5. Increased oxygen enzyme activity

6. Decreased glycolytic enzymes

7. Decreased cross sectional area of type II muscle fibers

8. Increased ratio of type IIa to type IIb fibers

9. No change in cross sectional area of type I fibers

10. Decreased maximum shortening velocity (Vmax) of type II fibers

11. Increased Vmax in type I fibers

12. Increased VO2 max

13. Decreased in leg strength

14. Decreased anaerobic capacity

15. Decreased %body fat

In laymen’s terms…………

1. Muscle fibers become smaller.

2. There were more capillaries per muscle (decreased fibers size), this allows for more blood to get to the muscles carrying oxygen and nutrients by shortening the distance the oxygen has to travel from capillary to muscle.

3. There were more of those cells that use oxygen for the muscle per muscle, increasing the availability of oxygen to the muscles.

4. Increased stores of different nutrients inside the muscles.

5. More oxygen being used by muscle cells.

6. Less production of cells that make fuel for the muscles.

7. Type II (fast twitch) muscle fibers become smaller.

8. Your muscles have adapted to performing moderate intensities over a longer duration, rather than short duration high intensity.

9. Type I (slow twitch) fibers stayed the same size.

10. The rate of contraction in the fast twitch fibers slowed down and now function more like slow twitch fibers.

11. Slow twitch fibers get slower also.

12. Able to take in and use more oxygen.

13. Legs get weaker.

14. Unable to work as hard/fast at short burst of activity running, jumping, etc.

15. You lost some fat!

Affects of Concurrent Endurance and Resistance Training

The common findings in the research suggested that subjects that participated in both regular resistance training and endurance training programs had:

1. resistance training improved leg strength by about 25%

2. increased anaerobic leg power which has been reported to be a critical determinant for success among endurance runners who have similar VO2 max values

3. increased Wingate anaerobic power

4. increased time to exhaustion at sub maximal work rates

5. increased lactate threshold at a given work rate

6. increased body weight and lean body mass

7. decreased %body fat

This translates into……

1. legs got stronger by about 25%

2. ability for legs to work harder/faster during short bouts got better, and this could be the difference between winning and loosing between two runners who can take in and use the same amount of oxygen

3. same as #2 but pertaining to cyclists

4. you can work longer at a more moderate rate and not get tired so easily

5. you can work longer/harder before you get that awful burning, aching in your muscles which cause you to slow down and eventually have to stop

6. you weigh more because you have more lean muscle on you

7. You lost fat!

In Conclusion……..

Resistance training alone can increase muscle mass, strength, power, and running speed but will not improve endurance performance. Endurance training alone can increase oxidative properties within the muscle tissues, and decrease body mass, but will not improve soccer specific skills (sprinting, decelerating, changing direction, jumping for headers, kicking, prevent injuries, etc.). Resistance training and sport endurance training together appears to be most beneficial to endurance sport performance providing that volume, intensity, and recovery time is monitored and adjusted to avoid overtraining and to produce the desired adaptations. Keep in mind, a general in-season strength training session (1-2 days/ week, 30-45 min) will have minimal volume in order to prevent overtraining meanwhile maintain the optimal physiological environment within the muscle tissues, cardiovascular, respiratory, and nervous systems.

I tried to keep this short, but there’s just so much information and some areas I still have not touched upon. Another important consideration is the neurological adaptations that resistance training has on propriception (sense of body awareness), core strength and motor control which are crucial in skill development, execution and injury prevention. I hope this has provided you with more knowledge regarding strength training during a season of soccer endurance training, and enables you to make a more informed and justified decision as to weather or not your athletes should lift during the season. My only regret is that I did not write this sooner.

Train hard, train smart!


Tanaka, H., Swensen, T. Impact of resistance training on endurance performance: A new form of cross-training? Sports Medicine, 25 (3), pp. 191-200, 1998.

Glowacki, S.P., et al., Effects of resistance, endurance, and concurrent exercise on training outcomes in men. Med. Scie. Sports. Exerc., 36(12), pp. 2119-2127, 2004.

Beth Byron, MS, CSCS

Strength Coach University of West Virginia


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