Concurrent strength and endurance training appears to inhibit strength development when compared with strength training alone. Our understanding of the nature of this inhibition and the mechanisms responsible for it is limited at present. This is due to the difficulties associated with comparing results of studies which differ markedly in a number of design factors, including the mode, frequency, duration and intensity of training, training history of participants, scheduling of training sessions and dependent variable selection. Despite these difficulties, both chronic and acute hypotheses have been proposed to explain the phenomenon of strength inhibition during concurrent training. The chronic hypothesis contends that skeletal muscle cannot adapt metabolically or morphologically to both strength and endurance training simultaneously. This is because many adaptations at the muscle level observed in response to strength training are different from those observed after endurance training. The observation that changes in muscle fibre type and size after concurrent training are different from those observed after strength training provide some support for the chronic hypothesis. The acute hypothesis contends that residual fatigue from the endurance component of concurrent training compromises the ability to develop tension during the strength element of concurrent training. It is proposed that repeated acute reductions in the quality of strength training sessions then lead to a reduction in strength development over time. Peripheral fatigue factors such as muscle damage and glycogen depletion have been implicated as possible fatigue mechanisms associated with the acute hypothesis. Further systematic research is necessary to quantify the inhibitory effects of concurrent training on strength development and to identify different training approaches that may overcome any negative effects of concurrent training.

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We compared changes in muscle fibre composition and muscle strength indices following a 10 week isokinetic resistance training programme consisting of fast (3.14 rad x s(-1)) or slow (0.52 rad x s(-1)) velocity eccentric muscle contractions. A group of 20 non-resistance trained subjects were assigned to a FAST (n = 7), SLOW (n = 6) or non-training CONTROL (n = 7) group. A unilateral training protocol targeted the elbow flexor muscle group and consisted of 24 maximal eccentric isokinetic contractions (four sets of six repetitions) performed three times a week for 10 weeks. Muscle biopsy samples were obtained from the belly of the biceps brachii. Isometric torque and concentric and eccentric torque at 0.52 and 3.14 rad x s(-1) were examined at 0, 5 and 10 weeks. After 10 weeks, the FAST group demonstrated significant [mean (SEM)] increases in eccentric [29.6 (6.4)%] and concentric torque [27.4 (7.3)%] at 3.14 rad x s(-1), isometric torque [21.3 (4.3)%] and eccentric torque [25.2 (7.2)%] at 0.52 rad x s(-1). The percentage of type I fibres in the FAST group decreased from [53.8 (6.6)% to 39.1 (4.4)%] while type IIb fibre percentage increased from [5.8 (1.9)% to 12.9 (3.3)%; P < 0.05]. In contrast, the SLOW group did not experience significant changes in muscle fibre type or muscle torque. We conclude that neuromuscular adaptations to eccentric training stimuli may be influenced by differences in the ability to cope with chronic exposure to relatively fast and slow eccentric contraction velocities. Possible mechanisms include greater cumulative damage to contractile tissues or stress induced by slow eccentric muscle contractions.

Athletic strength and power refer to the forces or torques generated during sporting activity. Their assessment can be used for strength diagnosis or talent identification, to monitor the effects of training interventions and to estimate the relative significance of strength and power to particular athletic pursuits. However, strength and power assessment is a difficult task. Reasons for this include: the fledgling status of research within the area, our limited understanding of the mechanisms underpinning strength and power performance and development, and limitations associated with various forms of dynamometry. This article describes a frame work for the collection of data which may ultimately lead to recommendations for the assessment of strength and power in sporting contexts. Such a framework will be evolutionary and depends upon synergistic improvements in our understanding of: the physiological mechanisms underpinning strength and power development; the effect that various training regimens have upon the development of strength and power; and factors influencing the validity and reliability of dynamometry. Currently, isometric, isoinertial and isokinetic dynamometry are employed in assessment. Each form has its supporters and detractors. Basically, proponents and critics of isokinetic and isometric dynamometry emphasis their apparently high internal and apparently low external [corrected] validity respectively. While the converse applies for isoinertial dynamometry. It appears that all 3 modalities can have acceptable reliability, however this should be established rather than assumed, as the reliability of each can be threatened by a number of considerations (e.g. instruction for isometric tasks, the impact of weight used during weighted jumping tasks, and the effects of gravity and feedback on isokinetic performance). While reliability is a seminal issue in assessment, it is not the only critical issue. Specifically, there has been little research into the correlation between strength and power measures and athletic performance. This work is central to the use of such indices in talent identification. To date, this work has generally been limited to heterogeneous rather than homogeneous groups. More work is required in this area. Furthermore, not all modes of assessment are sensitive or similarly sensitive to various training interventions. This suggests that these modalities are measuring different neuromuscular qualities. How these qualities relate to performance requires more work, and will determine the contexts in which various strength and power assessment modalities and protocols are used.(ABSTRACT TRUNCATED AT 400 WORDS)