Physical training programs for healthy adults in recreational and athletic settings frequently include a range of fitness components. Popular training methods in athletic populations include concurrent anaerobic strength and aerobic training (Tan et al. 2014). Traditionally these forms of exercise have been considered as mutually exclusive, with research indicating negative influences of on strength, power and anaerobic performance when endurance training is added to strength training (Dudley & Djamil 1985; Kraemer et al. 1995; Hennessy & Watson 1994). A growing body of evidence refutes this theory and shows little or no interference on the development of aerobic capacity or strength in strength development with concurrent strength and endurance training over a short term (Balabinis et al. 2003; Davis et al. 2008; Docherty & Sporer 2000).
Strength is defined as training can be defined as the maximal force that a muscle or muscle group can generate (Wilmore et al. 2008). Resistance training aims to increase strength via a combination of neurological and physiological changes to the central and peripheral (local) area. Initial gains in strength training programs are predominantly attributed to neural adaptations in synchronization of motor unit recruitment, increased rate of coding in motor units, autogenic inhibition and decrease in neural inhibition (Wilmore, J., Costill, D. and Kenney 2008). Longer term gains relate to transient and chronic hypertrophy of skeletal muscle, as individual muscle fibers increase in size.
Aerobic power can be defined as the rate of energy release by cellular metabolic processes that depend upon the availability and involvement of oxygen (McArdle et al., 2014). Performance increases that result from regular aerobic training can be attributed to multiple adaptations to the training stimulus. In a similar fashion to resistance training adaptations, changes occur locally and systemically. Changes in the muscles to increase efficiency of fuel substrate and oxygen transportation and utilization occur, as well as cardiovascular and pulmonary adaptations to improve oxygen intake and transportation.
Lundberg (2014) explains that endurance sports rely on aerobic metabolism and training aims therefore aims to sustain high power output over an extended duration. This is achieved through multiple central and local physiological adaptations. Increased maximal oxygen uptake is accomplished predominantly via an increase in cardiac output, and results in high aerobic power output. Work capacity is further amplified through local peripheral muscle adaptations such as increased muscle oxidative enzyme activity, mitochondrial and capillary density, and intracellular lipid stores.
Research shows a clear relationship between economy of movement (e.g. running economy) and strength training (Jones & Bampouras 2007). Running economy considers how efficiently a person uses oxygen while running at a certain pace and is a measure of running efficiency. Strength training has been shown to improve running economy, with a strong association between running economy and distance running performance. It is theorized that resistance training improves muscle strength, neurological characteristic as well as musculotendinous stiffness resulting in changes to the stretch shortening cycle in lower limb musculature improving efficiency of translation of ground reaction force into forward propulsion in more efficient use of energy, with an improved.
Although the skeletal muscle adaptations outlined above represent classical end - point adaptations to resistance and aerobic training, Lundberg (2014) notes that it should be acknowledged that phenotype changes occur in a continuum with numerous muscle adaptations showing minor specificity across exercise modes.
This complexity of the muscle adaptive response to exercise can be seen in muscle fiber changes that may increase in response to aerobic training and myosin transformation that occurs similarly regardless of exercise modality. Furthermore, high-volume resistance training may induce capillary proliferation and increased oxidative enzyme activity. Given the limited understanding of the mechanisms dictating classical adaptations to aerobic and resistance exercise, it is perhaps not surprising that the mechanisms regulating adaptation to concurrent exercise are poorly explored (McCarthy 2002).
In conclusion, the research suggests that for cardiovascular and cardiorespiratory adaptations in athletes, strength and endurance training are simultaneously compatible (Davis et al. 2008). However it should be noted that training adaptations may be impacted by chronic training, time allowed for recovery between exercise modes, and the training sequence. This should be carefully planned and periodised appropriately for the athlete.
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