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Friday, June 29, 2012

Human body has been designed to perform well when running without shoes


source: dw.world.de


Did you know that barefoot running might protect you from injuries? This is the result of the analysis published by the Harvard’s professor Daniel Lieberman. His first study was published in Nature in 2010 and the authors claimed that barefoot running may protect the lower leg from certain impact-related injuries.

The analysis showed that barefoot runners often land on the forefoot, sometimes with a flat foot but rarely on the heel. In the contrary, rear-foot landing is very common when wearing modern running shoes and this pattern of landing has been shown to create greater collision forces on the foot compared with the barefoot running.

Sources
Lieberman, Venkadesan, Werbel, Daoud, D’ Andrea, Davis, Mang’eri and Pitsiladis. Foot strike patterns and collision forces in habitual barefoot versus shod runners. Nature 463: 531-535, 2010.
Lieberman. What we can learn about running from barefoot running: an evolutionary medical perspective. Exercise & Sport Sciences Reviews 40: 63-72, 2012.

Wednesday, June 27, 2012

Hamstring injuries in soccer players: what’s new?



This week I read an ahead-of-print paper by van Beijsterveldt and colleagues (2012) which appeared in the Scandinavian Journal of Medicine & Science in Sports. This is a systematic review of the related studies with the aim to identify risk factors for hamstrings injuries in male adult soccer player.

What we already know
  • Hamstring injuries are common and account 12-16% of all injuries in soccer (Arnason et al., 2004).
  • Hamstring injuries may lead to an inability to play for up to 90 days and this might also be due to the high reinjury rate observed for this kind of injury.
  • Usually, hamstring injury occurs during rapid acceleration, deceleration, change of direction or during the last part of the swing phase of gait.
  • Potential risk factors for hamstring injuries are divided to intrinsic (age, previous injury, training history etc) and extrinsic (pitch type, environmental conditions etc).

What they found?
  • After evaluating the quality of the related studies, and excluding those with low quality from their analysis, the authors concluded that previous hamstring injury is the most significant risk factor to hamstring injuries.
  • Conflicting evidence exists on the role of hamstring length, hamstring flexibility and strength imbalances. In particular, some studies suggest that poor hamstring flexibility is a significant risk factor for hamstring injuries (Witvrouw et al., 2003) and others not (Engebretsen et al., 2010). The same holds for muscle strength imbalances (Croisier et al., 2008; Hagglund et al., 2006).

Related articles
  • Arnason et al. Risk factors for injuries in football. Am J Sports Med 32: 5S-16S, 2004.
  • Croisier et al. Strength imbalances and prevention of hamstring injury in professional soccer players: a prospective study. Am J Sports Med 36: 1469-1475, 2008.
  • Engebretsen et al. Intrinsic risk factors for hamstring injuries among male soccer players: a prospective cohort study. Am J Sports Med 38: 1147-1153, 2010.
  • van Beijsterveldt et al. Risk factors for hamstring injuries in male soccer players: a systematic review of prospective studies. Scand J Med Sci Sports 2012 Jun 21. doi: 10.1111/j.1600-0838.2012.01487.x. [Epub ahead of print].
  • Witvrouw et al. Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players. A prospective study. Am J Sports Med 31: 41-46, 2003.

Wednesday, June 20, 2012

Playing football at altitude: analysis of the FIFA 2010 World Cup data


Johannesburg, a host city for the 2010 World Cup,
located at an altitude of 1753m (photo from FIFA.com)

As you may know altitude affects exercise performance in a negative way. Actually, the reduction in oxygen partial pressure in the atmospheric air, as a result of altitude ascent, reduces oxygen availability to the working muscles and finally reduces athletic performance. Most of the results refer to laboratory studies and very little information exists in football.

The negative effect of altitude is observed in endurance events. Sprint performance seems to be better at altitude and this is due to the reduced air density. The reduced air density at altitude might also affect, at some degree, flying objects characteristics. In football, this means that altitude might affect flying ball characteristics and thus the result.

The aim of the study attached below was to examine the effect of altitude on football performance using match analysis data from 2010 World Cup. Let me remind you that the FIFA 2010 World Cup was staged in South Africa from June 11th to July 11th, 2010 and matches were played at cities of varying altitudes (0-1753m).

If you want to learn more about the study and the findings please connect to the official site at

Some references for further study are also shown below.
Hope you enjoy the reading.

References

  • Bartsch et al. Consensus statement on playing football at different altitude. Scand J Med Sci Sports 18: 96-99, 2008.
  • Gore et al. Preparation for football competition at moderate to high altitude. Scand J Med Sci Sports 18: 85-95, 2008.
  • Gore et al. Reduced performance of male and female athletes at 580m altitude. Eur J Appl Physiol 75: 136-43, 1997.
  • Hamlin et al. Simulated rugby performance at 1550-m altitude following adaptation to intermittent normobaric hypoxia. J Sci Med Sport 11: 593-599, 2008.
  • Levine et al. Effect of altitude on football performance. Scand J Med Sci Sports 18: 76-84, 2008.
  • McSharry PE. Altitude and athletic performance: statistical analysis using football results. BMJ 335: 1278-1281, 2007.
  • Perronet et al. Theoretical analysis of the effect of altitude on running performance. J Appl Physiol 70: 339-404, 1991.
  • Wehrlin et al. Linear decrease in VO2max and performance with increasing altitude in endurance athletes. Eur J Appl Physiol 96: 404-412, 2006.

Saturday, June 9, 2012

Are there genetic biomarkers to predict adaptability to training?

The study of genetic contribution to exercise training adaptation has emerged over the last years in an attempt to identify possible genes that regulate adaptability to training or trainability. These studies aimed to improve knowledge on effective health-related interventions and, hence, were on general population or unhealthy individuals (McPhee et al., 20120; Timmons et al., 2005).  However, information from these studies might shed more light into the potential molecular mechanisms explaining the observed large variability in training adaptations. Accordingly these findings might contribute in improving our understanding on why some players improve more than others.

Indeed, variability in maximum aerobic power improvement after training has been reported to range from 0% to >100% (Timmons et al., 2010). This means that some individuals show a big improvement whereas others no improvement at all. Causes of this wide range of inter-individual variability are poorly understood. Timmons et al. (2010) in his pioneer study has identified key genetic links to such variation. The authors defined a 29-gene expression signature in untrained skeletal muscle that explained >50% of the variance in VO2max improvements due to training.

One year later, Professor Claude Bouchard, a leader in genetics, identified genomic predictors of the response of VO2max to regular exercise. Interestingly, these genomic predictors were different from those presented by Timmons et al (2010). In Bouchard’s study, subjects who carried <9 favorable alleles at these 21 single-nucleotide polymorphisms (SNPs) improved their VO2max by 221 ml/min whereas those who carried >19 of these alleles improved by 604 ml/min. The 21 SNPs identified as predictors explained 49% of the variance in VO2max trainability. Although, the pre-training absolute values are not presented in this paper these results explain why there is such variation in human adaptive response to exercise training.

Conclusions and practical applications
  1. From these studies it appears that part of the variation in adaptation to exercise originates from variation in gene sequence that influences the complex cascade of biochemical events leading to adaptations to training.
  2. If there are genetic predictors of adaptation to training this means that in the future we might be able to select among talented players those with “high trainability”. We might also be able to create more effective training regimes for “low responders” but skilled players.

Points to consider before final conclusions
  • Studies so far have been conducted with white, non-elite athletes. We know very little for athletes and especially non-whites.
  • Most of the information is on VO2max although some data exist on resistance training adaptations. There is very limited information on other fitness attributes that have high impact on football performance.
  • As the authors of these papers acknowledge the relatively small sample size for this kind of research is a limitation of these studies. This however does not undermine, in my opinion, their significant contribution in advancing our current knowledge.

References
Bouchard et al. Genomic predictors of the maximal O2 uptake response to standardized exercise training programs. Journal of Applied Physiology 110: 1160-1170, 2011.
McPhee et al. Inter-individual variability in adaptation of the leg muscles following a standardized endurance training programme in young women. European Journal of Applied Physiology 109:1111-1118, 2010.
Petrella et al. Potent myofiber hypertrophy during resistance training in humans is associated with satellite cell-mediated myonuclear addition: a cluster analysis. Journal of Applied Physiology 104: 1736-1742, 2008.
Timmons et al. Human muscle gene expression responses to endurance training provide a novel perspective on Duchenne muscular dystrophy. FASEB 19:750-760, 2005.
Timmons et al. Using molecular classification to predict gains in maximal aerobic capacity following endurance exercise training in humans. Journal of Applied Physiology 108: 1487-1496, 2010.