Derek M. Hansen
Research Support Provided by Alex Pett
I always keep up with weekly injury reports during the NFL pre-season and regular season, as I know how injuries can make a significant impact on a team’s fortunes once the games begin. One statistic that I noticed more than others this year has been the high incidence of achilles tendon ruptures in the last few months. I had my staff sift through all the on-line injury reports and we came up with 13 achilles tendon ruptures in total. I’m not sure if there were more such injuries that went unreported or involved players that were eventually dropped from rosters, but 13 instances appears to be a rather large number, with the injured players at an average age of 25 years. This is in significant contrast to what was often considered an injury for veteran players over the age of 30.
I spoke with rehabilitation expert, Rob Panariello, on the subject and his sources confirmed that there were 20 achilles tendon ruptures from the last NFL season, which I still thought was a high number. A retrospective study from 2006 by Parekh et al. looking at achilles tendon ruptures in the NFL found there were 31 ruptures between 1997 and 2002 (an average of 5.2 per year), with the average age of injured player at 29 years. More recent reports have the total number of achilles tendon ruptures at six for 2008-2009. However, in 2011 there were 10 achilles tendon ruptures reported in the first 12 days of training camp, with another two more in the next 17 days. This season was preceded by a 130-day lockout that prevented players from attending off-season training sessions. The new collective bargaining agreement (CBA) was ratified in August 2011, but the implications for off-season training (or lack thereof) were not felt until the Spring of 2012 and the 2012-13 season.
With the growing number of non-contact lower body injuries, we have to ask ourselves, “Why is there a trend toward more severe, season-ending injuries, and how can we make changes to minimize the incidence of such injuries? First we must look at the various factors that are likely involved in the enhanced risk and probability of achilles tendon injuries. There is rarely one root cause, but rather a convergence of factors that lead to fertile ground for injury.
Coefficient of Friction and Adaptation Challenges
When there are significant increases in injuries to the lower extremities, particularly in non-contact scenarios, we have to look closely at the interaction of the players and the playing surface. This analysis must also look at the surfaces on which the players practice as well. Artificial grass-turf are much more prevalent over the last 10 years. Not to be confused with the AstroTurf carpets of the 1970’s and 1980’s, artificial grass-turf surfaces are designed to simulate the shock absorption and horizontal compliance qualities of natural grass. The first grass-like artificial turf field for the NFL was installed in 2002 at Seattle’s CenturyLink field. Currently, 13 of 32 teams have artificial turf fields in their home stadiums, while most teams have both a combination of natural grass and artificial turf fields in their practice facilities.
The reality of the situation with the newer artificial turf is that these surfaces have significantly higher coefficients of friction when combined with stiffer and lighter modern football cleats (resembling more of a track sprinting shoe) designed to provide maximum traction and reactivity. The term ‘coefficient of friction’ describes the ratio of force of friction between two bodies, as well as the force pressing the bodies together. The coefficient of friction greatly depends on the composition of the materials used. For example, steel ice-skate blades on an ice surface have a low coefficient of friction, while rubber race-car tires on an asphalt track have a high coefficient of friction.
A 2012 study published in the September issue of the American Journal of Sports Medicine sampled 2,680 NFL games played between 2000 and 2009, with 2,002 of those games played on natural grass and 678 games played on artificial turf surfaces. The NFL safety committee, known as the Injury Surveillance System (ISS), found that there were 1,528 knee sprains and 1,502 ankle sprains over this 10-year period. The ISS found that knee sprains were 22% higher on artificial turf surfaces than on natural grass. Increases in ACL sprints (67%) and eversion ankle sprains (31%) were identified for artificial turf versus natural grass.
I had a long discussion with legendary strength coach Al Vermeil about the greater incidence of injury and he brought up a very good point. He explained to me that the modern athlete’s nervous system simply cannot keep up with the changes in artificial surfaces and shoe technology. “Humans have evolved walking and running on natural surfaces. Now when an athlete tries to stop or change direction at high speed, the nervous system cannot make the necessary adjustments to safely complete the movement and protect the integrity of the joints involved.” Sport field cleats are also lighter but stiffer, ensuring that every movement from the athlete is translated directly into the sport surface. Add into the equation the fact that athletes are bigger, faster and stronger, and now you have a real problem.
Another factor in the turf versus grass issue is the fact that there is significant variation between these two surfaces throughout a season. It is not uncommon for teams to move practice from one surface type to another depending on where they are playing their upcoming game that week. If a team is playing on artificial turf on Sunday, some teams will schedule all practices on turf for that week. Conversely, some teams will second guess the issue and choose to stay on grass during the week of preparation to save the players’ legs and reduce impact and torque on the lower body. Intuitively, both of these decisions are common-sense approaches to the problem. However, as Al Vermeil accurately pointed out, the body and, more importantly, the central nervous system do not have adequate time to progressively adapt to the surface changes presented to the players. But, it leads us to the question, “How much time is enough time?”
During my time working with Charlie Francis, I found myself in many in-depth discussions of training elements and interaction of different variables. In one instance, he was telling me about the importance of training on grass surfaces for the sprinting athlete. This was about the time the Jamaicans were beginning to dominate the sprinting landscape with Asafa Powell and Usain Bolt. He believed the long periods of time spent training on grass surfaces, due to the fact there are not many quality rubberized track surfaces in Jamaica, actually helped them prepare for sprinting in competition. His explanation was two-fold. In one instance, training for many months on a softer, yet stable surface helped to strengthen the muscles and connective tissue below the knee joint, including calves, ankles and feet. The second benefit was a phenomenon that Charlie referred to as “tendon tuning,” where the tendons would stiffen to compensate for the softness of the ground, still allowing the athlete to deliver adequate power and elasticity on ground contact. (It is important to note that the opposite occurs when someone spends time training on hard surfaces. Tendons tend to soften to compensate for the increases in force of ground contact). After a relatively long training phase on the grass, once the athletes transitioned to track surfaces their muscle-tendon properties were optimized for fast sprinting. Strong enough to resist injury, while more elastic for speed. The take-home conclusions of this discussion were:
1. Adequate time (months of training) on the softer surface to create long-lasting strength and elastic properties for competition.
2. A gradual transition to artificial surfaces allowing for the body to adapt optimally and appropriately.
This concept was reinforced by my conversations with world-renowned plyometrics expert, Dr. Donald Chu, who had his jumping athletes (high jump, long jump and triple jump) perform jumping drills and bounding exercises on grass fields for a good portion of the preparatory period. As a result, his athletes had exceptional performances and competed relatively injury free.
In the case of football players moving from different surfaces from week to week, I would argue – applying the wisdom and logic of Al Vermeil – that there is not enough time for proper adaptation (both peripherally and centrally) to reduce the risk of muscle and tendon injury. While common sense would tell us that we need to make these short-term changes from surface-to-surface, we may be doing more harm than good.
A Lack of Adequate Preparedness
Another factor in the greater number of injuries, particularly in the pre-season and early stages of the regular season, is the athlete’s level of preparedness each year. In the old days of professional sport, training camp was an opportunity for players to get back into shape for the regular season. Because of the competitive nature of pre-season for roster spots and the need to get players up to speed on the coaches’ systems, training camp is no longer a place for a gradual build up of volume and intensity. Either you are ready to go, or you are ready to leave.
This reality places a heavy burden upon the players to come into camp ready. However, the definition of “ready” or “prepared” can vary significantly from player to player. Because the current NFL collective bargaining agreement does not require players to train with their teams for as many weeks as they did in previous years (down from 14 weeks to 9 weeks, with only three to four of those weeks truly dedicated to strength and conditioning work), a good proportion of players have accumulated less work to prepare them for the season. Many players are diligent and work with their teams outside of the mandatory off-season periods. Other players work with experienced private strength and conditioning coaches in other parts of the country. But we have to assume that there are a good number of players who don’t “get it done” in the off-season period, and put themselves at serious risk of injury once the pre-season and regular season begin. Casual conversations with performance coaches throughout the league reveal that some teams may only have 20-30% of players working with team staff during non-mandatory periods. One wonders what the other 70-80% of players are doing and if the workouts are providing appropriate preparation for the demands of the pre-season and regular season.
I have addressed the off-season training issue in previous articles, citing increases in the incidence of ACL and hamstring injuries. Now that we are experiencing distinct growth in the number of achilles tendon injuries over the last few years, will any measures be taken by the teams, coaches and players to ensure that injury numbers are reduced? As with any problem, the relevant parties must all come to agreement that the problem actually exists and then work together to develop strategies to improve the situation for players.
Aren’t Injuries a Part of the Game?
Common comments from fans of the game are often, “The players know what they are getting into. Injuries are a part of football. Easy come, easy go.” While we all agree that football can be a violent and unforgiving game, I still believe that a lot can be done to minimize the occurrence of season-ending and career-ending injuries. In the 2006 study by Parekh et al, it was determined that of the 31 athletes who ruptured their achilles tendons, only 21 (64%) were able to return to play in the NFL. Of those 21 players who did return, there was a significant drop in the number of games played per year and the quality of play in the three years post-injury. Thus, the occurrence of a severe injury such as an achilles tendon rupture can mean the end of a career, or at least a significant drop in the level of performance of a player. While I understand that people often use the term “Not For Long” when in reference to the NFL, I still believe that every strategy and resource possible be used to resolve some of these challenges.
We have to consider all of the possibilities for the causes of achilles tendon ruptures and other similar career-ending injuries. Looking at the data on the surface can sometimes be deceiving and absolute conclusions should never be drawn on a relatively small number of data points. In some professional sports, league expansions result in a larger pool of players that can skew the data and give the impression of growth in injuries. In the case of the NFL, a long-term investigation and subsequent plan for injury prevention must be established with the sport and the League. A reactive approach will not work, given the magnitude of the issues and variables involved. This includes an approach to facilities, equipment, off-season training and in-season management of training and injuries. Everyone involved, including the owners, coaches, players, agents and the union, has a vested interest to improve the landscape when it comes to safety and injuries.