Research Review - Volume 4
By Sean Maloney
Welcome to Research review and your latest summary of sport and exercise science research.
This month's research demonstrates a potential application to almost every type of training – something for every sport and vocation. The studies featured have attempted to examine a diverse selection of topics including restpause training, static stretching and squat depth.
Remember: Train hard, train SMART!
Optimising load positioning during weighted jumps
Weighted jumps are often included in power training programmes: such ballistic exercises are thought superior to traditional resistance exercises for developing power. This study reviewed how the position of load affects the biomechanics of the exercise.
Twenty-nine male rugby players each performed weighted jumps with a regular barbell and a hexagonal (hex) barbell in addition to an unloaded control (body weight). Jumps were performed with loads equivalent to 20%, 40% and 60% of each subject's predetermined 1 RM back squat. Recorded values for jump height, peak force, peak power, and peak rate of force development were all higher when jumping with the hex bar compared to the regular barbell. Jumping with the hex bar and a load of 20%1 RM elicited the highest power output. Peak power production during the unloaded jump was higher than in each of the regular barbell trials.
- Outcome: performing weighted jumps with the load positioned at arm's length appears to be preferential for developing lower body power.
Swinton PA, Stewart AD, Lloyd R et al. Effect of load positioning on the kinematics and kinetics of weighted vertical jumps. J Strength Cond Res, 2012, 26, 906–913.
An evaluation of the rest-pause method
The rest-pause method is a type of 'cluster' training which generally involves breaking up a prescribed number of repetitions into as few sets as possible whilst using short rest periods (10–30 seconds). This allows a greater volume and/or intensity of work to be performed in a shorter period of time. While various such techniques are widely used in bodybuilding circles, this particular method has a potential application for each and every type of trainer. To date, there has been little research evaluating its effectiveness.
Fourteen resistance-trained males completed 20 repetitions of the back squat exercise, at a set load of 80% 1 RM, using three different protocols. Protocol A consisted of five sets of four repetitions with a 3-minute rest interval between sets; protocol B of five sets of four repetitions with a 20-second rest interval between sets, and the rest-pause protocol was an initial set to failure and then subsequent sets following a 20- second rest interval. Maximal force and rate of force development (RFD) were measured during an isometric squat before, immediately after and at 5 minutes post exercise. The activity of six different hip and thigh muscles was recorded using electromyography (EMG). Subjects completed the restpause method in 2.1±0.4 sets with a total protocol duration of 103 seconds; while protocols B and A were completed in 140 and 780 seconds, respectively. All protocols elicited similar decreases in force and RFD upon completion, which was fully recovered at 5 minutes post exercise. Increased motor unit recruitment was observed in the rest-pause protocol for all muscles measured.
- Outcome: rest-pause techniques appear a time-efficacious training modality which may facilitate increased motor unit recruitment.
Marshall PWM, Robbins DA, Wrightson AW et al. Acute neuromuscular and fatigue responses to the rest-pause method. J Sci Med Sport, 2012, 15, 153–158.
Get stronger to get faster
Sprint speed is a key performance determinant across a wide range of team and individual sports. Previous research has shown a strong relationship between lower body strength and sprint speed, particularly over shorter distances, but less research exists as to the extent to which improvements in strength transfer to sprint performance.
The sprint performance of 19 professional rugby league players was evaluated before and after completing an 8-week periodised training programme: 5m, 10m, and 20m sprint times were recorded. Players performed lower body strength and conditioning sessions twice a week along with two additional plyometric and agility sessions. The training programme resulted in an 18% improvement in 1 RM squat performance and decreases in sprint time of 7.6%, 7.3% and 5.9% over 5m, 10m and 20m, respectively.
- Outcome: improvements in sprint performance appear to reflect improvements in maximal squat performance.
Comfort P, Haigh A, Matthews MJ. Are changes in maximal squat strength during preseason training reflected in changes in sprint performance in rugby league players? J Strength Cond Res, 2012, 26, 772–776.
Caffeine is metabolised in the liver by the cytochrome P450 (CYP) system of enzymes, the 1A2 (known as CYP1A2) enzyme in particular. A single nucleotide (adenine/ cytosine) polymorphism, a variation in a single base pair of DNA coding, at intron 1 of the CYP1A2 coding gene, has previously been shown to affect caffeine metabolism and health responses to caffeine ingestion.
Individuals carrying a cytosine (C) allele may experience less induction of the CYP1A2 enzyme, and therefore a slower metabolism of caffeine, than those carrying 2 adenine (A) alleles (AA homozygous) . For this reason, caffeine may increase the risk of coronary heart disease in those expressing a C allele .
1. Sachse C, Brockmoller J, Bauer S et al. Functional significance of a C-->A polymorphism in intron 1 of the cytochrome P450 CYP1A2 gene tested with caffeine. Br J Clin Pharmacol, 1999, 47, 445–449.
2. Cornelis MC, El-Sohemy A, Kabagambe EK et al. Coffee, CYP1A2 genotype, and risk of myocardial infarction. J Am Med Assoc, 2006, 295, 1135–1141.
Caffeine responders vs non-responders
Although caffeine is widely used and accepted as an ergogenic aid, its effect varies largely between individuals. Researchers from James Madison University, USA examined the role of a specific gene (CYP1A2) in determining the performance-enhancing potential of caffeine; no previous studies had identified a specific gene mutation (polymorphism) that might account for such variation.
Thirty-five male, recreationally competitive cyclists completed two 40km time trials on a cycle ergometer. Trials were performed one hour after the ingestion of a drink containing either 6mg/kg of caffeine or a placebo. Following the time trials, samples of the cyclists' DNA were analysed and they were subsequently categorised as either AA homozygotes (n=16) or C allele carriers (n=19), according to the CYP1A2 polymorphism which they carried. Performances of the AA group were improved by an average of 4.9% following caffeine ingestion whereas performances in the C group were improved by 1.8%.
- Outcome: individuals homozygous for the A allele of the CYP1A2 gene appear to carry a larger potential for performance enhancement following caffeine ingestion.
Womack CJ, Saunders MJ, Bechtel MK et al. The influence of a CYP1A2 polymorphism on the ergogenic effects of caffeine. J Int Soc Sports Nutr, 2012, 9, 1.
Squat deep to be more explosive
Squat depth is often a source of controversy. Squatting below parallel has been shown to increase the contribution of the glutes, key for developing power, but squatting with a limited range will allow you to use more weight, potentially resulting in a greater training stimulus. Researchers from Frankfurt, Germany examined how training with a specific squat depth affects responses to training.
Thirty-six male and 23 female physical education students, with limited strength-training experience, were assigned to one of three training groups according to jumping ability, which aimed to match the groups' ability prior to training. These groups trained with either deep free-weight back squats, deep free-weight front squats or partial Smith machine back squats (quarter squats). The students trained twice a week for a period of 10 weeks. Countermovement and squat jump performances were improved in both deep squatting groups but not in the quarter squat, or a control group who did not perform any training exercise.
- Outcome: squatting with free weights and a full range of motion appears to elicit greater improvements in lower body power production than partial Smith machine squats.
Hartmann H, Wirth K, Klusemann M et al. Influence of squatting depth on jumping performance. J Strength Cond Res, February 2012, [epub ahead of print]. doi: 10.1519/JSC.0b013e31824ede62 (accessed 15 May 2012).
Static stretching improves ROM without neuromuscular adaptation
Static stretching is widely utilised in an attempt to increase range of motion (ROM) at a specific joint. Understanding the precise adaptations which may occur as a consequence of prolonged stretching regimens is important as this will enable us to develop the most effective and efficient protocols. Hayes et al. sought to investigate the possible neuromuscular origins for the improvements in ROM achieved through static stretching.
Forty healthy subjects were allocated to either a stretching group or a control group. The stretching group performed five stretching sessions per week for a period of 6 weeks. The stretching sessions consisted of five repetitions of three separate stretches, each performed for a duration of 30 seconds. Stretches were performed to each individual's maximum tolerance.
Dorsiflexion ROM and electromyography (EMG) of the soleus were measured in both groups before, halfway through (3 weeks) and at the conclusion of the programme. The stretching group saw improvements in dorsiflexion from 0–3 weeks and from 3–6 weeks, and dorsiflexion was increased by 42% after 6 weeks of static stretching. No initial signs of neuromuscular adaptation were apparent from the EMG data.
- Outcome: static stretching is an appropriate technique to increase ROM at the ankle joint, such improvements being a likely consequence of mechanical adaptation and/or increased stretch tolerance.
Hayes BT, Harter RA, Widrick JJ et al. Lack of neuromuscular origins of adaptation after a long-term stretching program. J Sport Rehabil, 2012, 21, 99–106.
The effect of volume on running injuries
Whilst evidence shows a link between running volume and injury, such relationships have not been established in highperformance team sport. As explained by the authors, previous studies have attempted to quantify training loads using subjective measures. This study explored this relationship using global positioning system (GPS) as an objective monitor of training activity.
Thirty-four elite Australian rugby league players participated in the study. Over an entire season, activity during 117 skill training sessions was tracked using GPS and lower-body softtissue injury data was prospectively recorded. The relative risk of transient injury (resulting in no training time lost) was 2.7 times greater when sprinting (classified as >7m/s) exceeded 9m per session whilst the risk of injury resulting in missed competition was 2.9 times higher when high-intensity running (>5m/s) exceeded 175m per session. Moreover, lower volumes of acceleration were associated with a lower relative injury risk (Table 1).
- Outcome: restricting the volume of high-velocity movements in preparation for competition may be warranted in elite team sport athletes.
Gabbett TJ, Ullah S. Relationship between running loads and soft-tissue injury in elite team sport athletes. J Strength Cond Res, 2012, 26, 953–960.
Sean Maloney is a strength and conditioning coach, lecturer and writer. He works with both the London Sport Institute and Middlesex University, UK, and runs strength and conditioning company, Maloney Performance.