Answers to questions.
last update, 1 June/91, 1997
1. training cycles.How much rest time is necessary between heavy, strength building excercise sessions? Explain the reasons for this.
Depending on the individual, the recovery time for the muscles is from 1 to 2 days. Heavy excercises 3 times a week is about the right amount.
2. muscle control hierarchy. A weight lifting session with high reps of small weights will not develop larger muscle masses. Explain this in terms of the muscle control hierarcy and the process of muscle building.
Low force demands will only excite the forces that are LOW on the hiearchy of motor units [control units for the muscle groups]. The large force muscles will not be used if ONLY small forces are demanded. No matter how many reps are used, only the small force muscles [usually slow twitch]muscles will be excercised.
3. force for muscle at 75% of rest length. Characterize the percentage of maximum muscle force at 75% of rest length and at 50% of rest length. About how much more work is done if the athlete prestretches to 120% of rest length compared to starting from rest length.
We can use the graph of force vs muscle length.
75% 75% of To
50% zero force.
120% 120% of To
The amount of work that can be done by the prestretching is considerably more than the work done by the muscle contraction from the rest length. I have estimated the area under the Force-length curve in the volume9 for a contraction from rest and from 120% of rest length. The area is proportional to work. The ratio of work is 1.5. A ball with 50% more kinetic energy would have 23% more velocity. The prestretching is obviously important.
4. Consider a muscle with a length of 0.4m and a cross section of 10 cm^2. Make a qualitative estimation at the muscle speed that produces the highest power output.Estimate the power output. Estimate the power output when the muscle contraction speed is reduced to 1/2 of the velocity which produces the maximum power.
Since the mucles produce 30-100 N/cm^2, and the speed of contraction is about 2-4 L/sec. For this particular muscle, [using the max values] To = 1000N, Vmax = 1.6m/s.
Power-max = 0.1*To*Vmax = 0.1*1000*1.6=160 watts at a muscle velocity of about .48m/s
At .15 Vmax, the Power = 0.8*power max = 128 watts. [see graph in volume 9]
5. If an athlete can hold 500 lb for a short time. Estimate the weight that can be lifted at 1/2 the maximum speed of the muscle.
To is proportional to 500 lb.
At V=0.5 Vmax, T= 0.2To.
Weight lifted is 0.2*500 = 100 lb at half the maximum muscle speed. This is a big reduction in force.