Concurrent Strength and Endurance Training
Proposition for Debate - by Andrew Burne
Contents
- Statement of the Topic
- Introduction
- Strength and Endurace Adaptions
- Concurrent Training Studies
- Modality Of Resistance Training
- Modality of Endurance Training
- Training History
- Proposed Mechanisms
- Conclusion
- References
Statement of the Topic
Concurrent Strength and Endurance Training
Introduction
Concurrent strength and endurance training is undertaken by numerous athletes in various sports in an effort to achieve adaptations specific to both forms of training. Literature findings to date, investigating the neuromuscular adaptations and performance improvements associated with concurrent strength and endurance training (referred to as concurrent training) have produced inconsistent results. Some studies have shown that concurrent training inhibits the development of strength and power, but does not effect the development of aerobic fitness when compared to either mode of training alone. Other studies have shown that concurrent training has no inhibitory effect on the development of strength and endurance.
Strength and Endurace Adaptions
Strength and endurance training regimes represent and induce distinctly different adaptive responses when performed individually. Typically, strength-training programs involve large muscle group activation of high-resistance low-repetition exercises to increase the force output ability of skeletal muscle (Sale et al 1990). In contrast, endurance-training programs utilise low-resistance, high-repetition exercises such as running or cycling to increase maximum O2 uptake (VO2max). Accordingly, the adaptive responses in skeletal muscle to strength and endurance training are different and sometimes opposite (Tanaka and Swensen 1998).
Strength training has been reported to cause muscle fibre hypertrophy, associated with an increase in contractile protein, which contributes to an increase in maximal contractile force (Sale et al 1990). Strength training also reduces mitochondrial density and suppresses oxidative enzymes activity which can cause impede endurance capacity, but has minimal impact on capillary density or in the conversion of muscle fibre types from fast twitch (type II fibres) to slow twitch (type I fibres) (Nelson et al 1990, Sale et al 1990). In contrast, endurance training usually causes little or no muscle fibre hypertrophy, but it does induce increases in mitochondria content, citric acid enzymes, oxidative capacity and the possibility of muscle fibre conversion from fast twitch to slow twitch (Bell 1991, Nelson et al 1990).
Many competitive endurance athletes incorporate resistance training into their training in a hope to improve endurance performance. However, as previously mentioned adaptations to exercise are generally considered to be specific to the training type of stimulus (Nelson 1990). Although, many adaptations are specific to the type of training, some changes that occur with resistance training could influence endurance performance, which include: muscle fibre transformations and muscle fibre (type I) hypertrophy, which may alter fibre recruitment patterns and help prevent muscle fatigue, as less motor units need to be activated for the same work load (Bishop and Jenkins 1999). Bishop and Jenkins (1999) analysed endurance performance in 21 female subjects over a 12-week program of strength training. They found that strength training did not reduce endurance performance and may actually improve endurance capacity in the long term. Tanaka and Swensen (1998) suggested that runners and cyclists may improve endurance performance via a resistive weight training program, due to increases in the size of type I fibres, changes in type II subtype ratios, and myofibril contractile properties. These changes may allow individuals to exercise longer at a given submaximal work rate by reducing the force contribution from each active myofibre or by using fewer myofibres. In conjunction, the myofibre changes may also allow individuals to delay the recruitment of less efficient type II fibres (Tanaka and Swensen 1998). They also indicated that a swimmers endurance capacity benefited only from an "in-water" resistance program specific to their swimming stroke, relative to a standard weights program usually given to these athletes. The "in-water" resistance program incorporates the use of biokinetic swim benches and reverse current hydrochannel swimming. This may imply that resistance training for swimming needs to be specific to their stroke to achieve any improvements in endurance performance.(Tanaka and Swensen 1998).
Overall, the literature on endurance and strength programs suggests that the nature of the adaptive responses to training is specific to the training stimulus. McCarthy et al (1995) also concluded, that strength and endurance programs may be antagonistic when combined together (concurrent training) due to these opposing adaptations acquired from each mode in isolation.
Concurrent Training Studies
Concurrent training programs involving strength and endurance exercises are commonly performed by athletes to achieve adaptations specific to both forms of exercise. Research investigating the effects of concurrent training has typically compared changes in strength and endurance variables after strength training, endurance training or concurrent strength and endurance training.
Concurrent training studies investigating endurance and strength performance to date have shown mixed results. Nelson et al (1990) reported that improvements in maximal oxygen uptake (VO2max) during the second half of a 20-week programme were compromised when strength training was implemented into an endurance program. In contrast, a number of studies have found no interference to strength or endurance development as a consequence of concurrent training (Sale et al 1990, Bell et al 1991, McCarthy et al 1995). Sale et al (1990) suggested that resistance training performed on the same day as endurance training may impede strength development when compared to training for either on separate days.
Overall, the most consistent finding from concurrent training literature to emerge was that concurrent training can inhibit strength and power when compared to strength training alone (Hickson1980, Hennessy and Watson 1994, Hunter et al 1987, Kraemer et al 1995). However, no studies have demonstrated or suggested possible mechanisms for the observed reductions in strength development when utilising a concurrent program. A summary of recent concurrent studies, their methods and findings are listed in Table I.
It is difficult to make clear statements as to under what conditions such inhibition occurs, as there are significant differences in the design of concurrent training studies. To assess the results found in the literature the critical components that will influence outcomes must be analysed. These include, the resistance training modalities, endurance training modalities and training history.
| Author | Training | Findings |
|---|---|---|
| Hickson (1980) | 10 weeks training - 5 days per week
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| Hunter et al (1987) | 12 weeks training - 4 days per week
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| Dudley and Dajamil (1985) | 7 weeks training - 3 days per week
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| Sale et al (1990) | 22 week program - 3 times per week 2 groups - S one leg and C the other;
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No interference with development of strength or endurance |
| Hennessy and Watson (1994) | 8 weeks training - 5 days per week
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| Abernethy and Quigley (1993) | 7 week program - 3 days per week
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No interference in strength development |
| Kramer et al (1995) | 12 week training - 4 days per week
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| McCarthy et al (1995) | 10 week training - 3 days per week
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| Nelson et al (1990) | 20 week program - 4 days per week
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| Bell et al (1991) | 16 week training - 3 days per week
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Modality Of Resistance Training
The majority of concurrent training studies involving isoinertial strength training demonstrated an inhibition in strength development (Hickson et al 1989, Dudley and Djamil 1985, Hennessy et al 1994, Kraemer et al 1995). This inhibition appears to be confined to the musculature involved in both the endurance and strength training components of the concurrent training program (Hennessy et al 1994, Leveritt et al 1999). Furthermore, all but one of the studies involving isoinertial strength training that have measured muscular power, show that strength training alone increases muscular power, while concurrent training produces no improvement in muscular power (Hennessy et al 1994, Kraemer et al 1995, Leveritt et al 1999). Concurrent strength and endurance training does not seem to affect the development of isokinetic strength at slow speeds (<1.68rad.s-1) of muscular contraction (Nelson et al 1990). However, it has been suggested that lower body isoinertial strength at fast speeds (>1.68rad.s-1) of muscular contraction does appear to be inhibited (Leveritt 1999, Abernrthy and Quigley 1993).
Abernethy and Quigley (1993) noted that lower body strength development appears to be compromised when the lower limbs are engaged in simultaneous endurance and strength exercises. However, concurrent training may not restrict the development of upper body strength. Unfortunately, only one study conducted to date has examined upper body adaptations and therefore more research is necessary before any conclusions can be made regarding the effect concurrent training has on upper body strength development (Leveritt 1999).
Modality of Endurance Training
All studies that have incorporated running as the endurance training modality have demonstrated an inhibition in strength development (Hickson 1980, Kraemer et al 1995). Interestingly, each of these studies involved a combination of running and isoinertial strength training. However, studies that involved cycling, have shown inconsistent patterns of interference (Leveritt 1999).
Training History
The development of strength in trained and untrained subjects has been shown to be compromised after a concurrent training program (Dudley and Djamil 1985, Sale 1990). In contrast, no inhibition in strength development has been observed after concurrent training in both trained and untrained participants (Bell 1991, McCarthy 1995).
Hunter et al (1987) showed that athletes had significantly greater increases in strength and power after a concurrent training program when compared to a sedentary group of volunteers who performed the same program. However, this study did not include a group of endurance athletes who performed strength training in isolation. Therefore, it is unclear whether previous endurance training either partially or fully negates any inhabitory effect on strength development associated with concurrent training (Lervitt 1999).
Proposed Mechanisms
The majority of concurrent training studies have demonstrated that strength development is inhibited during concurrent strength and endurance training programs. However, few authors have attempted to identify why this phenomenon exists (Lervitt 1999). Possible mechanisms have been suggested, which include over-training, conflicting physiological adaptations, muscle fiber type transformations, hypertrophy, endocrine changes, and muscular or neural adaptations.
Over-training
Dudley and Fleck (1987) suggested that individuals performing concurrent strength and endurance training may become over-trained relative to subjects who perform strength or endurance training alone. It is thought that this overtrained state causes the concurrent training group to have less than optimal improvements in performance tests following training (Leveritt et al 1999). However, Dudley and Djamil (1985) implied that over-training is not responsible for the lack of strength development as they only used relatively low volumes of exercise with sufficient rest relative to other studies. Therefore, there is insufficient evidence in the literature to suggest over-training as the mechanism for inhibited adaptive response seen in some concurrent studies.
Conflicting Physiological Adaptations
When subjects undertake concurrent training programs the muscle is placed in a situation of conflict, were the muscle is attempting to adapt to both forms of training. However, this is not possible because adaptations to strength training are often inconsistent with adaptations observed during endurance training. Endurance training has been shown to increase the activity of aerobic enzymes and mitochondrial density (Nelson et al 1990, Sale et al 1990). However, aerobic enzyme activity may be decreased after strength training (Nelson et al 1990). The muscle is therefore unable to adapt optimally to either the strength or endurance training stimulus. Concurrent training therefore elicits different adaptations at the skeletal muscle level compared to each mode of training when performed in isolation, which may cause a lack of development in either strength or endurance.
Muscle Fibre Transformation
Concurrent training studies that have measured training-induced muscle fibre type transformations have reported little difference between concurrent and strength training groups (Dudley and Djamil 1980, Sale et al 1990, McCarthy et al 1995). Both concurrent and endurance training programs have been shown to stimulate similar muscle transformations from type II fibres to type I fibres (Tanaka and Swensen 1998). However, there is insufficient evidence in the literature to date to suggest that different muscle type transformations resulting from concurrent training is the cause of the lack of strength development in individuals.
Muscle Fibre Hypertrophy
Strength training has been shown to increase the cross-sectional area of skeletal muscle (Dudley and Djamil 1980). Hypertrophy in both slow and fast twitch muscle fibres has been observed after strength training (McCarthy 1995). While resistance training causes greater fibre hypertrophy than endurance training, controversy exists over the extent of muscle fibre hypertrophy resulting from endurance training. Unlike strength training, there appears to be no distinct pattern of fibre hypertrophy associated with endurance training (Leveritt et al 1999). This suggests that concurrent strength and endurance training may elicit different patterns of fibre hypertrophy from those normally observed when performing either mode in isolation (Nelson et al 1990). However, there is no evidence in the literature to suggest that different patterns of muscle hypertrophy are associate with any inhibition in strength development often observed after concurrent training.
Endocrine Changes
Concurrent training altering the balance of anabolic and catabolic hormones may reduce fibre hypertrophy and consequently strength development (Leveritt et al 1999). Typically, testosterone and cortisol have been used as markers for muscle anabolism and catabolism. Kraemer et al (1995) showed that resistance-training interventions altered testosterone : cortisol ratio levels in favour of anabolism. They also suggested that the endurance element of concurrent training programs could create a more catabolic environment (relative to strength training in isolation), and this in turn may inhibit strength development. Although, this is a proposed endocrine mechanism for lack of strength development, no studies have shown testosterone levels to be reduced in a concurrent program. Therefore, the current data indicates that further research is required into the role of anabolic-catabolic hormones in strength development in concurrent programs.
Motor Unit Recruitment
It has been suggested that concurrent training may alter motor unit recruitment patterns associated with maximal voluntary contractions (McCarthy et al 1995). Endurance training has been shown to reduce vertical jump height (Leveritt et al 1999). This may be due to endurance training reducing the capacity of the neuromuscular system to rapidly generate force. It has been suggested that concurrent training may therefore interfere with the development of strength, by impairing the ability of the neuromuscular system to make adaptations in the organisation of efficient motor unit recruitment patterns normally associated with strength training in isolation (Leveritt et al 1999).
Acute Fatigue
Residual fatigue has been suggested to occur following the endurance component of a concurrent program, which may compromise the ability of muscles to develop tension during the strength element of concurrent training (Hennessy and Watson 1994). If sufficient tension cannot be generated during the strength component of a concurrent program, optimal strength development and adaptations may not occur. It has been suggested by Craig et al (1991), that if the endurance training is performed prior to the strength training, residual fatigue may impair muscular force out-put and thus impair strength development. Sale et al (1990) also found that concurrent strength and endurance training performed on alternate days produced larger strength gains than concurrent training performed on the same day, which indicates that residual fatigue from endurance training is a possible mechanism responsible for the observed inhibition in strength development.
Conclusion
Concurrent strength and endurance training inhibits the development of isoinertial strength when compared with strength training alone. Concurrent training interferes with lower body isoinertial strength development at fast (>1.68rad.s-1) but not slow speeds (<1.68rad.s-1) of muscular contraction. The effect endurance training has on strength development when associated with concurrent training programs is unclear. However, it has been demonstrated that endurance running combined with resistance training appears to inhibit isokinetic strength development when compared with isokinetic strength training alone. It has also been indicated that subjects with a history of endurance training may be less susceptible to any negative effects of concurrent training on strength development.
Concurrent strength and endurance training appears to inhibit strength development when compared with strength training alone. At present there are a few hypotheses including overtraining, conflicting physiological adaptations, muscle fibre type hypertrophy, endocrine changes or acute fatigue as the proposed mechanisms for lack of strength development associated with concurrent training. However, there is lack of conclusive evidence in this region as many of the concurrent training studies are single study investigations which examine adaptations to specific forms of strength and endurance training. It is also difficult to compare results in the literature when studies differ markedly in their design factors including mode, frequency, intensity, frequency of training and training history of subjects. Therefore, further research is required to investigate these causes and identify other possible mechanisms responsible for the observed inhibition in strength development after concurrent training.
References
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