There are two types of muscular soreness– acute and delayed. Acute soreness is due to muscle ischemia (lack of adequate blood flow). Delayed soreness (onset 24 to 48 hours after exercise) could be due to torn muscle tissue or muscle spasms but is more likely due to disruption of the connective tissues, including the tendons. There is no known prevention or cure for soreness, however, stretching exercises may relieve it when present and may sometimes prevent or delay its onset. Delayed muscular soreness is greatest following eccentric contractions and is least following isokinetic contractions.
With isotonic strength programs, there is no single combination of sets (number or repetitions performed consecutively) and repetition maximums (maximal load that can be lifted a given number of repetitions before fatiguing) that yields optimal strength gains. However, most programs should include between one and three sets with repetition maximums between three and nine. Although improvement in strength and muscular endurance can be greater with low repetitions and low resistances, respectively, equal increases in strength and endurance have been found with either program.
Isometric programs can significantly increase strength by training 5 days per week, with each training session consisting of 5 to 10 maximal contractions held for 5 seconds each. Isometric endurance can also be improved, but the design of such a program varies considerably.
Eccentric exercise programs, in comparison with isotonic and isometric programs, are not any more effective in developing strength and endurance. They may excel, hover, in developing eccentric contraction strength.
Isokinetic programs are speed specific (i.e. they cause maximal gains in strength and endurance at velocities of movement equal to or slower, but usually no faster, than the training velocity). Gains in isokinetic strength and endurance can be made with programs consisting of as little exercise as 1 minute per day, 4 days per week, for 7 weeks (total time= 28 minutes). In theory and in comparison with other programs, isokinetic programs should lead to the greatest improvement in muscular performance. Once gained, strength and endurance are retained fro relatively long periods of time.
Circuit training consists of a number of stations where a given weight-lifting exercise is performed within a specified time. It, too, is an effective training technique for improving muscular strength, muscular endurance and to a lesser extent, flexibility and cardiovascular endurance.
Although a few studies suggest little or no improvement in speed of contraction, most show that weight-training programs do increase both speed and power of contraction. Specific sports skills can be significantly improved through weight-training programs. Flexibility, the range of motion about a joint, is related to health, and, to some extent, to athletic performance. Regularly scheduled programs involving stretching exercises (2 to 5 days per week, 15 to 30 minutes a day) will improve flexibility within a few weeks.