The kinematic, kinetic and blood lactate profiles of continuous and intra-set rest loading schemes

Abstract

The optimisation of strength and power through resistance training has been the source of debate amongst health professionals and researchers for many years. As resistance training involves the repeated activation and contraction of skeletal muscles, continuous training will ultimately result in a failure to sustain the training intensity especially when performing multiple sets and / or repetitions. Therefore the prescription of rest periods within the training session becomes an important consideration. Relatively short rest periods (60-90 seconds) have been traditionally used for the maximal strength adaptation involving increases in the cross-sectional area of the muscle, whereas longer rest periods (180-300 seconds) have traditionally been used for the maximal strength adaptation involving enhancement of neural function and maximal power adaptation. However, there is very little scientific evidence to support these current practices. In fact, the effect of different rest periods on maximal strength and power development has received very little research attention. Additionally, research that has been conducted in this area has been typified by a number of methodological inconsistencies, within and between studies, which confound scientific understanding. Although traditionally resistance training has employed continuous training schemes with inter-set rest periods, intra-set rest training methods which distribute rest intervals between groups of repetitions have also been investigated. It has been theorised that the short rest periods within the training set allow partial resynthesis of the intramuscular phosphocreatine stores, potentially allowing an athlete to increase their training volume by training at high intensities for longer durations, or performing additional repetitions (Berg, 2003). This is thought to lead to an increased exposure of the muscle to the kinematic and kinetic stimuli thought important for strength and power adaptation whilst minimising performance-inhibiting metabolic accumulation and substrate depletion. However, research into intra-set rest training schemes is still in its infancy, and many of the theories surrounding intra-set rest training are currently unsubstantiated. It is thought that examinations of the acute kinematic, kinetic and blood lactate profiles of continuous and intra-set rest training schemes may enhance scientific understanding regarding the efficacy of intra-set rest training. The purpose of this study was to investigate and compare the acute kinematic, kinetic and blood lactate responses to continuous and intra-set rest loading schemes. Nine male subjects performed an isoinertial Smith machine bench press task (6RM load) with a continuous loading scheme (CONT), an intra-set rest loading scheme equated by total rest time, volume and load (ISRV) and an intra-set rest loading scheme equated by total rest time and load (ISRR). The order of the loading schemes was assigned in a block randomised order with a minimum of 48 hours recovery between each testing session. Attached to the bar of the Smith machine was a linear position transducer that measured vertical displacement with an accuracy of 0.01cm. Displacement data was sampled at 1000Hz and collected by a laptop computer running custom built data acquisition software. Finger prick blood lactate samples were taken from the non-dominant hand using sterile techniques at the following time points: pre-exercise (Pre), immediately post-exercise (P0), five (P5), fifteen (P15) and thirty minutes (P30) post exercise. Blood glucose samples were taken pre-exercise only. It was observed that manipulating the rest period, by increasing the frequency but decreasing the length of each rest period, did not significantly influence the kinematics and kinetics associated with resistance training, but did have an effect on the post-exercise blood lactate response when the load, rest duration and training volume was equated (ISRV). This finding may be of practical significance if fatigue is important in strength development or conversely if power training needs to be performed with minimal fatigue. It was also observed that increasing the frequency of the rest period enabled the subjects to perform a greater number of repetitions (ISRR), resulting in significantly greater kinematics, kinetics and blood lactate accumulation. It may be speculated, therefore, that ISRR training may offer a superior training stimulus for the development of maximal strength and hypertrophy than CONT training methods, as ISRR loading increased the exposure of the muscle to the kinematic, kinetic and metabolic stimuli thought important for the development of these qualities.