Table 1: A comparison of bodybuilders and powerliftersCharacteristic Bodybuilders Powerlifters
Type IIb fiber size (3,15,26) Smaller Larger
Type II fiber number (13,26,27) Lower Higher
Capillary density (3,11,15,27,28) Higher Lower
Tolerance to lactic acid (29) Higher Lower
Sarcoplasmic volume (30) Higher Lower
Mitochondrial density (3,15,30,32) Higher? Lower
Activate lipolysis during training (13) Yes No
Total number of muscle fibers (30) Same? Same?Adaptations in capillary density and mitochondrial volume are affected by the
specifics of the training program and are linked to lactic acid levels. Generating high amounts of
lactic acid (using long set times, around 60 seconds) may stimulate capillary growth and
increases in mitochondria similar to what is seen with aerobic training.
Several authors have suggested 20 to 60 seconds as the ideal time range for muscle
growth (23-25) and we might tentatively subdivide that time period into the adaptations listed in
table 2.
Table 2: Set time and the possible adaptations seenTime/set #Reps * Primary Adaptation seen
5-20 seconds 1-5 Neural improvement
20-30 seconds 4-6 Growth of Type IIb fibers
30-45 seconds 12-15 Growth of Type IIa fibers
45-60 seconds 25+ Increased sarcoplasmic volume (glycogen,
mitochondria, capillaries, etc).* assumes 3-5 seconds per repetition.Section 2: What Causes Muscle Growth?
Weight training results in an alteration in the rate of protein synthesis and degradation
(34,35). Following resistance training, levels of 3-methylhistidine (a marker of protein
breakdown) increase (34) and protein synthesis increases over the next 24-36 hours (36-38).
Although the exact stimulus for growth is not known, research supports one or more of the
following factors as critical to stimulate growth: high tension, metabolic work, eccentric muscle
actions and the hormonal response to training (33,39-41). Additionally, sufficient nutrients and
protein must be available to support the synthesis of new muscle proteins. Each factor is
discussed in further detail.