Does lifting slow make you slow? What the science tells us

by  Brett Holland, PT, DPT CSCS 09/25/2015

Overview

-The human body is generally considered to have 3 muscle fiber types

• Type I=slow twitch (oxidative)
• Type IIa=fast twitch oxidative glycolytic (meaning fast but also has some endurance properties)
• Type X= ultra fast (glycolytic)

What are the normal percentages of each?

• Costill et al. found untrained individuals to have roughly 50% fast twitch and 50% slow twitch [1]
• Elite weightlifters tend to have more fast twitch fibers (60%) [2]
• In an excellent literature review, Wilson et al. stated, “athletes in sports requiring the greatest aerobic and endurance capacities have slow twitch fiber percentages as high as 90–95%, whereas athletes in sports requiring greater anaerobic capacities, strength, and power (e.g., weight lifting and sprinting) have fast twitch fibers ranging from 60 to 80%[1,9,17]”[3]

Can the percentages of fast and slow twitch fibers be changed?

We don’t really know at this point there is limited evidence

• There is some data showing no change in fiber types with exercise
• There is some data showing changes in fiber percentages with the incorporation of ballistic contractions
• In general, the less rest, the lighter the weight, and the more repetitions you perform = greater influence on slow twitch fibers
• The more rest, heavier weight, faster movement speed ,and less repetitions = greater influence on fast twitch fibers

How do these percentages influence performance?

• There has been positive research data indicating that the more slow twitch fibers present equates to improved performance in endurance events.  The same has been demonstrated for fast twitch fibers in sports requiring high amounts of speed and power.
• Fry et al. found strong correlations between fast twitch fibers (IIa) and performance in the snatch, vertical jump power, and countermovement jump power in Olympic weight lifters[4].

How does training influence fiber shifting?

• The available data at this point shows that ballistic contractions have the highest influence on fiber shifting (explosive contractions)
• Liu et al. compared traditional weight lifting vs a combined lifting and ballistic routine on muscle fiber composition of the triceps (3 days a week for 6 weeks)[5].
• The ballistic group incorporated 10 explosive concentric bench throws and 10 explosive push-ups for 5 sets on 2 separate days
• Results: Conventional group=decrease type X (ultra fast), increase type IIa (fast), no change in type I
• Ballistic group=no change type X (ultra fast), increase in type IIa, and decrease in type I. 
• Conclusion:  high velocity movements may help shift slow twitch fibers to fast twitch fibers [5]

What does this mean?

• It simply means that high velocity movements should be part of your training program to help shift slow twitch type I fibers to fast twitch type IIa.

Bottom Line:

• Power athletes like baseball players should avoid low intensity endurance work because it reduces power and may potentially cause fiber shifting from fast twitch to slow twitch.
• Power athletes shoulder incorporate ballistic type contractions to improve explosive strength and potentially help shift slow twitch fibers to fast twitch (IIa).

References

1. Costill DL, Daniels J, Evans W, Fink W, Krahenbuhl G, Saltin B. Skeletal muscle enzymes and fiber composition in male and female track athletes. J Appl Physiol 40: 149–154, 1976. http://www.ncbi.nlm.nih.gov/pubmed/129449

2. Widrick JJ, Stelzer JE, Shoepe TC, Garner DP. Functional properties of human muscle fibers after short-term resistance exercise training. Am J Physiol 283: R408–R416, 2002.http://www.ncbi.nlm.nih.gov/pubmed/12121854

3.  Wilson, Jacob M., Jeremy P. Loenneke, Edward Jo, Gabriel J. Wilson, Michael C. Zourdos, and Jeong-Su Kim. “The Effects of Endurance, Strength, and Power Training on Muscle Fiber Type Shifting.” Journal of Strength and Conditioning Research (2011): 1. NSCA. Web.https://www.researchgate.net/publication/51632406_The_Effects_of_Endurance_Strength_and_Power_Training_on_Muscle_Fiber_Type_Shifting

4.  Fry AC, Schilling BK, Staron RS, Hagerman FC, Hikida RS, Thrush JT. Muscle fiber characteristics and performance correlates of male Olympic-style weightlifters. J Strength Cond Res 17: 746–754, 2003. http://www.ncbi.nlm.nih.gov/pubmed/14666943

5.  Liu Y, Schlumberger A, Wirth K, Schmidtbleicher D, Steinacker JM. Different effects on human skeletal myosin heavy chain isoform expression: Strength vs. combination training. J Appl Physiol 94: 2282–2288, 2003. http://jap.physiology.org/content/jap/94/6/2282.full.pdf