Does muscular size necessarily mean muscular strength? Well... yes and no. Strength training in general, results in an increase in cross-sectional area of all fiber types. This type of increase is called hypertrophy (1,3,4,6) or the increase of muscle fiber size. While strength training increases type I muscle fibers, greater hypertrophy will occur in type II muscle fibers.
Program design is ultimately what will affect the amount of hypertrophy seen in type I and type II muscle fibers. Training for strength and power (as in powerlifting) requires maximal to near maximal contractions together with very low repetitions and full recovery between sets. This particular type of training has been shown to cause more hypertrophy in type II muscle fibers than type I muscle fibers (7). This is very important for strength and power athletes because type II muscle fibers have much stronger contractions than type I muscle fibers (5). Bodybuilders, who utilize lower intensity contractions with higher volume and shorter rest periods, do not demonstrate the selective hypertrophy of type II muscle fibers as with strength and power athletes. Instead, bodybuilders have been shown to have a greater degree of hypertrophy in type I muscle fibers (2).
In short, muscular size may be caused from either hypertrophy of type I or type II muscle fibers. However, strength and power gains are from the selective hypertrophy of the stronger type II muscle fibers. Training protocols that utilize heavy weight and very low reps with at least 3 minute rests between sets have been shown to increase the size of type II muscle fibers best.
1. Abernethy, P.J., Jurimae, J., Logan, P.A. etal. (1994). Acute and chronic response of skeletal muscle to resistance exercise. Sports Medicine. 17: 22-38.
2. Conroy, B.P. and Earl, R.W. (1994). Bone, muscle, and connective tissue adaptations to physical activity. Essentials of Strength Training and Conditioning. T.R. Baechle, ed. Champaign, IL: Human Kinetics.
3. Fleck, S.I., and Kraemer, W.J. (1987). Designing Resistance Training Programs. Champaign, IL: Human Kinetics.
4. MacDougal, J.D. (1993). Hypertrophy or hyperplasia. Strength and Power in Sports. P.V. Komi, ed. London: Blackwell Scientific. pp. 230-238.
5. Narici, M.V., Roi, G.S., Landoni, L. et al. (1989). Changes in force, cross-sectional area and neural activation during strength training and detraining of the human quadriceps. European Journal of Applied Physiology. 59: 310-319.
6. Tesch, P.A. (1988). Skeletal muscle and adaptations consequent to long-term heavy resistance exercise. Medicine and Science in Sport and Exercise. 20(S): 132-134.
7. Wathen, D. (1994). Periodization: concepts and applications. Essentials of Strength Training and Conditioning. T.R. Baechle, ed. Champaign, IL: Human Kinetics, pp. 459-472.
MS, RD, CSCS, MSS
Strength and Conditioning Coach
Sport Nutrition Consultant