January 2013

Lower extremity effects of detraining in athletes

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istockphoto.com #10636395

Evidence suggests that when an athlete stops or tapers his or her training, the resulting effects on endurance, strength, balance, and lower extremity biomechanics may increase the risk of injury. Understanding these effects can help prac­ti­tioners minimize injury risks.

By Boyi Dai, PhD, and Jason C. Gillette, PhD

Acute and chronic lower extremity injuries are common in sports. Lower extremity injuries can result in pain, time loss, and increased risk of secondary injury for athletes and can create an economic burden for society.1,2 To avoid the negative consequences caused by lower extremity injuries, prevention is the key. Previous investigators have focused on developing effective training programs that can decrease injury risks and rates. For example, balance training can increase stabilometric performance and decrease ankle sprain injuries.3-5 Neuromuscular training can decrease biomechanical risk factors for anterior cruciate ligament (ACL) injury and ACL injury rates.6-8 However, while the effects of training on lower extremity injury risk have been widely studied, the potential effects of detraining on injury risk have received less attention.

Detraining is defined as partial or complete loss of training-induced adaption as a consequence of insufficient training stimulus.9 Detraining can be induced by many factors, such as illness, injury, a postseason break, retirement, or a change in environment. Understanding the effects of detraining on athletes’ endurance, strength, balance, and lower extremity biomechanics can provide insight on the related lower extremity injury risks.

Effects on endurance and strength

Mujika and Padilla9,10 reviewed short- and long-term detraining effects on physiological, endurance, and strength adaptations. Short-term was defined as less than four weeks, and long term was defined as more than four weeks. The authors summarized that short-term detraining could decrease maximum oxygen uptake, blood volume, maximum cardiac output, and endurance in highly trained athletes. Decreases were observed in muscle capillary density, oxidative enzyme activities, and fiber cross-sectional areas. However, decreases in strength were small. With regard to long-term detraining, the decreases in cardiovascular fitness and endurance became more significant, especially for recently trained individuals. Muscle fiber areas declined significantly, while strength reduced slowly.

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istockphoto.com #14879196

Decreased endurance may predispose athletes to early fatigue, which has been suggested as a risk factor for lower extremity injuries. Fatigue may decrease ankle somatosensory function,11,12 which could increase the risk of ankle injury.13 Several studies have demonstrated decreased sagittal plane motion and increased nonsagittal plane motion during landing tasks following a fatigue protocol.14-16 This rigid landing pattern has been associated with increased ACL loading.1 Fatigue also has been associated with increased risk of lower extremity injury in running.17,18 If an athlete is exposed to the same practice or competition intensity as in his or her pre-detraining period, the early onset of fatigue may increase injury risk.

Reductions in strength are also of concern, since previous investigators have associated muscle weakness with changes in lower extremity biomechanics.19,20 In addition, muscle strength can play an important role in maintaining balance following perturbation.21 Therefore, the decreased muscle strength induced by detraining might increase lower extremity injury risk. Strengthening exercises can improve lower extremity biomechanics22,23 and, if performed during the offseason, may provide a countermeasure to the detraining effects that would otherwise occur.

Detraining effects on balance

Balance and postural control refer to an individual’s ability to maintain a position, respond to a perturbation, and perform voluntary movements. Balance has been prospectively indentified as a risk factor for ankle sprain13,24 and secondary ACL injury.25 Previous studies regarding detraining effects on balance have been conducted mostly in older adults. Training was improved older adults’ balance and lowered fall risks, but the effect was partially or completely lost after the termination of training.26-28

Kouzaki et al29 studied the effects of 20-day bed rest with or without strength training on postural sway in healthy young adults. One group of volunteers was prohibited from doing any physical activity. Another group performed dynamic calf-raise and leg-press exercises. After the bed rest period, plantar flexor muscle volume decreased in the nonactivity group but was maintained in the strength-training group. However, both groups had increased center of pressure mean velocity during eyes-open and eyes-closed double-leg standing.

Detraining effects on balance in athletes have received very little attention. Dai et al30 studied the effect of a one-month postseason break on postural control in collegiate female volleyball athletes. Eleven highly trained athletes were analyzed during eyes-closed
single-leg stance at the end of the fall season and at the beginning of the next year’s spring season. During the fall season, the athletes trained for 20 hours per week, including practice, conditioning, and competition. During the one-month postseason break, they participated in self-selected training, but the average training duration decreased to 2.7 hours per week.

The athletes’ center of pressure sway standard deviation and velocity during the single-leg stance test were significantly higher after the break than before detraining. This decrease in postural control might increase the risk of ankle sprain. The conclusions that can be drawn from this study are limited by its pre- and post-testing design, relatively small sample size, and focus on a single sport. Considering the strong association between balance and injury risks, further studies are needed.

Effects on lower extremity biomechanics

Injuries usually occur during highly demanding tasks or result from accumulated stress during repetitive tasks. Examining the movement patterns associated with high-risk tasks provides straightforward information relating mechanical loading and injury risks. A few studies have been conducted to identify lower extremity biomechanical variables that may predict injuries.25,31,32 Many studies have looked at interventions to improve lower extremity mechanics, with the goal of injury prevention.3,6,7 However, information about the effects of detraining on lower extremity biomechanics is still lacking.

In the study by Dai et al,33 female volleyball athletes were tested while performing a stop-jump task before and after the postseason break. Athletes demonstrated decreased jump height, decreased knee flexion during the early landing phase, and decreased prelanding muscle activation on EMG (electromyography) for the vastus lateralis and biceps femoris muscles. However, no significant differences were found for nonsagittal plane biomechanics and landing EMG for the quadriceps and hamstring muscles. The decreased jump height suggested a decrease in functional performance. Because knee flexion plays an important role in loading the ACL,1 the decreased knee flexion might result in an increased risk of ACL injuries.

Prapavessis et al34 investigated the immediate effect and retention of soft landing instruction on landing force in children aged between 8 and 10 years. After receiving instruction the participants decreased their peak ground reaction force during landing. However, the improvement was only temporary and disappeared after three months with no additional instruction.

Padua et al35 studied the effects of training duration on the retention of movement pattern changes in youth soccer athletes. Athletes’ movement patterns were evaluated using a Landing Error Scoring System immediately before and after a training program to improve landing mechanics and three months following the training program. One group of athletes trained for three months, while another group trained for nine months. Interestingly, though landing patterns in both groups improved immediately after the training, only the nine-month training group retained the improvement three months after training.

Previously mentioned studies suggested a negative effect of detraining on lower extremity biomechanics, while some other studies showed the cessation of training might not necessarily negate the training effects.

Barber-Westin et al36 studied the retention of improvement in knee separation during landing in high school female volleyball players. After six weeks of neuromuscular training, 11 of 16 athletes increased their knee separation; these 11 athletes retained the improvements after one year. Onate et al37,38 studied the immediate effects and retention of different feedback modalities on lower extremity biomechanics during jump landing tasks. They found the positive effects of immediate augmented feedback on landing force and knee joint range of motion can be retained one week after training in young adults.

Overall, detraining could have negative or neutral effects on lower extremity biomechanics. Detraining effects might differ according to detraining durations and modalities, athletic populations, and selective biomechanical variables.

Summary

Detraining is usually induced by reduction or stoppage of regular physical activity. Detraining effects on endurance and strength have been well documented. Because there is a lack of research connecting endurance and strength to actual injury rates, the potential effects on injury risks remain speculative. Poor balance has been prospectively identified as an injury risk factor. Balance is likely to decline after the cessation of a training program in older adults. However, there is a lack of research regarding detraining effects on balance in athletes.

Detraining could also cause changes to lower extremity biomechanics and thus increase injury risk. Current biomechanics research is too limited to make definite conclusions about detraining effects on injury risk. However, the results of preliminary studies tend to be consistent with epidemiological studies. Hootman et al39 summarized 16 years of National Collegiate Athletic Association (NCAA) injury surveillance data for 15 sports: One finding was that, for all sports, the preseason practice injury rate (6.6 injuries/1000 athlete exposures) was much higher than the in-season (2.3 injuries/1000 athlete exposures) and postseason (1.4 injuries/1000 athlete exposures) practice injury rates. Although many factors might contribute to the high preseason practice injury rates, one potential explanation could be that athletes started the season with detrained physical capacities and movement patterns that increased their injury risk.

Further studies are needed to answer some practical questions regarding detraining effects. First, it is important to know the detraining effects induced by schedule changes relative to the competitive season. For example, many NCAA athletes train for 20 hours a week during the spring and fall semesters. With an understanding of how detraining caused by summer and winter breaks might affect athletes’ performance and injury risk, practitioners can develop training programs for different stages of the season and offseason.

In addition, while many investigators focus on the positive effects caused by injury prevention training, the retention of any training effects is as important as the immediate training effect. If the training effect is retained, athletes might be able to spend more time on skill training and less time on injury prevention. If the retention of training effects is of short duration, practitioners might consider incorporating the injury prevention programs into daily training.

Clinical implications

Detraining can have negative effects on an individual’s physical capacities, balance, and movement patterns and thus increase injury risks. To minimize the detraining effects on injury risks, one strategy is to minimize detraining. During postseason breaks, athletes might conduct maintenance training to avoid a sudden and rapid drop in training stimulus. Coaches and clinicians need to develop guidelines for athletes to conduct their own training during postseason breaks.

A second strategy is to emphasize fundamental endurance, strength, balance, stability, and technique training during the early practice phase following detraining. Injuries are more likely to occur during competitions than practice.39 Engaging athletes in competitions with high intensity reactions and perturbations before they have recovered fundamental capabilities might elevate injury risks. Before coaches or clinicians apply injury prevention training programs, they should keep in mind that training effects could be limited to a certain time frame. Injury prevention training might need to be conducted regularly and persistently to be effective in the long term. Sport-specific training and injury prevention training should be balanced according to movement requirements and injury risks.

Additionally, detraining effects can vary among different individuals. Therefore, it is important to conduct regular screening at various stages of a complete season and offseason to quantify and monitor the training and detraining effects. Laboratory-based biomechanical testing is highly accurate and can precisely identify deficits in human movement patterns,30,33 but the high cost and resource demands might limit its application.

There are many clinically applicable tools that can be used for screening. For example, the single-leg stance test30 and the Y balance test40 can be used for balance screening. Functional movement screening is a good tool to assess functional deficits of the whole body.41 Force plates or sensors with a single vertical axis can identify asymmetries in force distribution.42 Movements can be recorded using off-the-shelf camcorders and evaluated using validated scoring systems.35 These evidence-based measurement tools are relatively inexpensive and can be used by team members. Coaches and clinicians are encouraged to obtain these skills and apply them to screening.

We need to know when detraining occurs and what its effects are on functional movements. We can then develop specific training programs to minimize detraining effects and injury risks.

Boyi Dai, PhD, is an assistant professor in the Division of Kinesiology and Health at the University of Wyoming in Laramie. Jason C. Gillette, PhD, is an associate professor in the Department of Kinesiology at Iowa State University in Ames.

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