Strength and Endurance Training
Studies show that concurrent strength and endurance training can have an inhibitory effect on the development of both strength and endurance (Nelson 1990) or strength only (Hennessy & Watson 1994). Other studies found no inhibitory effect with concurrent strength and endurance training (Sale 1990, Bell 1991, Hortobagyi 1991).
Enhancement of Cardio Performance
A study by Hickson et al. (1988) found that adding strength training to endurance training enhances short term, high intensity endurance and does not inhibit aerobic function or performance.
When performed in succession, Chtara, et. al (2005) found that strength circuit training immediately after individualized endurance training in the same session produced greater improvement in the 4 km time trial and aerobic capacity than the opposite order or each of the training programs performed separately.
Concurrent sprint interval training and strength training does not inhibit strength gains when compared to strength training alone, however the addition of sprint interval training improves aerobic performance measurements such as VO2max (Cantrill 2014).
Endurance Work Inhibits Power
Dudley & Djamil (1985) reported concurrent strength and endurance training in the same muscle does not inhibit cardiovascular improvement (VO2 max), however, it did reduce the ability to increase peak torque at fast velocities. Slow velocity contraction was unaffected. Similarly, a study by Kraemer et al. (1995) demonstrates that strength training does not impair endurance training adaptations, however, endurance training can inhibit speed and power development by decreasing the Type I muscle fibers.
Santtila et al. (2009) studied military basic training of the Finnish Defense Forces. They concluded that the large amount of endurance-based military training interfered with the soldier's strength and power development.
Effects on Deconditioned Subjects
Deconditioned subjects may not experience an inhibitory effect when strength and endurance training is combined. Simultaneous strength and endurance training does not appear to negatively influence power, strength and aerobic fitness development in girls following a detraining period (Santos 2011) or sedentary college aged women (Volpe 1993). Hickson (1980) reported that concurrent strength and endurance training inhibited strength development only after the 8th week of training but did not affect the magnitude of increase in VO2max.
Although strength improvements are seen with concurrent strength and endurance programs, muscle fiber growth is inhibited as compared to those that perform strength training alone (Karavirta 2011).
Techniques to Lessen Concurrent Training Inhibition
Cycling appears to be somewhat less disruptive to strength adaptations as compared to running. The author theorize cycling is slightly less disruptive to strength gains since the cycling biomechanics more closely resemble multi-joint strength training movements such as the Leg Press or the Squat. (Gergely 2009).
Santtila et al. (2009) suggested that the Finnish Defense Forces decrease in the amount of endurance-based military training and/or an increase in the amount of maximal explosive strength training in their basic training protocols in order to optimize strength and power development in their soldiers.
Overreaching and overtraining have been proposed as possible reasons for inhibition of progress during concurrent training. Hormonal changes associated with overtraining inhibit type 1 muscle fibers hypertrophy. Adequate recovery, reduced training volume, and well-planned periodization techniques (eg: classic periodization or block periodization) may allow for progress in multiple fitness components (Kraemer 2012). Kraemer (2012) also makes additional suggestions:
- Conduct training needs analysis
- match training with sports requirements
- Elimination of extraneous training
- which does no match the metabolic demands of the sport
- more aerobic training than what is required
- exercise as a punishment
- Insure adequate resistance training stimuli
- Value quality over quantity
- Value recovery and rest in a conditioning program
- Decrease prolonged periods of high intensity coupled with high volume
- Monitor progressions and capacities
- Implement sports practice assessments
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