According the S.A.I.D principle, Specific Adaptations will occur as a result of Imposed Demands.
If you tax the Cardio-vascular system, the majority of the improvements / adaptations will occur in the Cardio-vascular system.
- Increased number of Mitochondria = more aerobic energy is produced.
- Increased capillary density = improved blood flow into the muscle
- Increased Haemoglobin concentration in blood = better O2 transport to muscle
- Increased stroke volume and cardiac output by the heart = more O2 delivered to the muscles.
- Increases the force production capacity of the muscle.
- Increases the strength of the Contractile Proteins: Actin and Myosin
- Improves the ability of the muscle to apply forces as a result of Nervous system adaptations.
- Possible hypertrophic response of the Slow Twitch Fibers to the Medium resistance - High volume training paradigm.
- Improves co-ordination and synchronization of muscle groups during activity.
- A transformation of the overall percentage of FT-A fibers compared with FT-B fibers
Recent research studies (primarily in distance runners) have shown that incorporating Rt training aimed at enhancing Power i.e. 3-5 sets for 3-6 repetitions at ≥ 85% of max and a program of Plyometric focused training, an increase in movement economy and and endurance performance can be realized.
This is a result of increased power production by the muscle. Basically, the Power training focuses on the strength of the muscle and the Plyometric work focuses on the speed component, resulting in an increase in overall performance.
As a side note, none of the studies found any changes to the measures of the Cardio-vascular conditioning as a result of the Power and Plyometric training..
This is important because it shows that improvements in performance are as a result of better muscular recruitment patterns and better force development which then translates into more economical movement, which results in better athletic performance..
The key take away here is: when assigning resistance training to your endurance athletes, keep intensity high and volume low: 3-5 sets for 3-6 repetitions at ≥ 85% of max.