The Journal of Strength & Conditioning Research

Introduction

The 40-yd dash is the premier test used for evaluating sprint speed among American football players at all levels (^{1,6,7,9,10,14-16}). It is a fundamental test of straight-ahead speed used in recruiting and evaluating players in all divisions of college competition (⁷) and in assessing player potential for the professional level (^9,14). Like many tests of athletic performance, it has gained popularity through anecdotal support for its usefulness. It is thought that the legendary professional coach Paul Brown reasoned that 40 yd was about as far as a typical player would have to run on any given play (⁸). Once inculcated into the lore of the game, it has become the accepted gauge of speed at all positions and is difficult to supplant with other tests (⁸).

The traditional method of timing the 40-yd dash in football players has been the use of handheld stopwatches operated by coaches with varying degrees of experience in the use of such devices (⁸). The scientific study of the variability and accuracy to be expected among timers using handheld watches is limited. The most precise method of timing for the 40-yd dash is by electronic methods, and yet little documentation of the difference to be expected between handheld watches and electronic timing has been presented (^4,11). Some sources appear to accept the 2 methods as equal because they allow either when reporting 40 yd sprint times (^1,14). Fry and Kraemer (⁷) suggested adding 0.20 seconds to hand times to represent electronic times in the 40-yd sprint. The official track and field manual indicates that the difference between hand timing and electronic timing should be 0.24 seconds (¹³), although limited experimental data appear to be available to confirm this value.

With so much emphasis placed on the importance of the 40-yd dash, it would be beneficial for football coaches and strength and conditioning specialists to evaluate the degree of variation to be expected among hand timers. In addition, documentation of the degree of difference between hand timing and electronic timing would be useful. Therefore, the purpose of this study was to assess the difference among experienced testers in hand timed 40-yd dashes and to determine the degree of difference between hand timing and electronic timing in collegiate football players.

Methods

Experimental Approach to the Problem

Sprint speed is routinely measured in American football players at all levels of competitions by the 40-yd dash. Despite the importance placed on this test, there appears to be no standards suggested to maintain consistency of measurement. The majority of 40-yd dashes are timed by individuals with varying levels of experience using handheld stopwatches. We have attempted to document the amount of variability to be expected among hand timers and the degree to which hand times might differ from electronic timing in a competitive testing environment for college football players.

Subjects

Fifty-nine National Collegiate Athletic Association (NCAA) Division II college football players served as subjects after having the study explained and signing informed consent documents. This study was approved by the Institutional Review Board of the university before testing. Players had been involved in competitive football for a minimum of 7-11 years and had extensive experience performing short sprints as part of their conditioning and testing program. The highly competitive atmosphere of the conclusion of the 12-week winter off-season training program provided excellent motivation for peak performance. Throughout the 12 weeks, players performed sprint and agility drills twice per week. Testing was performed after 2 days of rest with no physical training. The physical characteristics of the subjects are presented in Table 1.

Procedures

Hand Timing

Each player performed an all-out 40-yd dash on an indoor synthetic track. Players wore cotton shorts, T-shirts, and rubber-soled athletic shoes. A standard team warm-up was administered 15 minutes before testing. In addition, each player was encouraged to undergo individual warm-up procedures throughout testing.

Players performed the sprint individually starting from a traditional 3-point football stance. Each player was timed simultaneously by 7 experienced timers using digital stopwatches (model SC-505, Robic Inc, Orange, CA, USA) in the traditional manner most frequently used in college football. Each timer had a minimum of 5 years of practice using a stopwatch and spent time learning the characteristics of their stopwatch used in this study. The timers were positioned perpendicular to the finish line with 4 on one side and 3 on the other. Timers were instructed to initiate their watches on the first movement of the player from the 3-point stance. No communication was permitted among the timers or with the electronic clock operator throughout the testing periods to avoid any procedural adjustments during testing.

Electronic Timing

Electronic timing was performed using a switch mat (model 63515; Lafayette Instruments, West Lafayette, IN, USA) placed on the starting line and a photoelectric gate (model 63501-IR; Lafayette Instruments) positioned 70 cm above the running surface at the finish line. The electronic timer (model 54035; Lafayette Instruments) was triggered by the player lifting his dominant hand from the switch mat and stopped when he passed through the infrared beam at the finish line.

To assess intertrial and interrater reliabilities, 32 players were randomly selected to perform a second trial. After each player's first sprint, a minimum of 5-minute recovery was given before he was allowed to perform the second sprint. Timers had no knowledge of the player's previous time when measuring the second sprint.

Statistical Analyses

A repeated measures analysis of variance with Bonferroni post hoc follow-up was used to determine significant differences among the hand times and electronic timing. Interrater reliability was determined using the intraclass correlation coefficient (ICC). Intertrial differences were assessed using a paired t-test. Intertrail reliability for hand and electronic timing were determined using ICC. The ICC was also used to assess the consistency of the difference between hand timing and electronic timing.

Results

The mean for all timing methods and the differences between hand timing and electronic timing are presented in Table 2. Intraclass correlation coefficients for hand vs. electronic timing were very high and not significantly different among the hand timers (Table 2). Five of the 7 hand timers did not differ significantly (p > 0.05) in their values, with the remaining 2 timers significantly slower yet not significantly different from each other. The maximum difference among the hand timers on any given trial was 0.19 ± 0.14 seconds (95% confidence interval [CI] = −0.08 to 0.46 seconds). The minimum difference among the hand timers on any given trial was 0.12 ± 0.13 seconds (95% CI = −0.13 to 0.37 seconds). The average difference among all pairwise comparisons of hand timers (n = 1,239) was 0.02 ± 0.12 seconds (95% CI = −0.22 to 0.26 seconds). Interrater reliability among all hand timers was ICC = 0.987 (95% CI = 0.981-0.991).

The average of the 7 hand times (4.85 ± 0.28 seconds) was significantly faster (p < 0.001) than electronic timing (5.16 ± 0.28 seconds) producing an average difference of −0.31 ± 0.07 seconds (95% CI = −0.44 to −0.18 seconds). The difference between hand timing and electronic timing was consistent across all times according to the Bland-Altman procedure (²) (Figure 1). The maximum difference between hand timing and electronic timing was −0.42 ± 0.12 seconds (95% CI = −0.18 to −0.66 seconds), and the minimum difference was −0.23 ± 0.07 seconds (95% CI = −0.09 to −0.37 seconds). The ICC between electronic timing and hand timing was 0.985 (95% CI = 0.975-0.991).

The second trial (n = 32) was significantly faster (p < 0.01) than the first trial in 75% of the players tested (Table 3). Despite the number of players who improved, there was no significant pattern to the difference in times according to the Bland-Altman method (Figure 2).

Only 1 hand timer had a significantly faster time on the second trial. The differences between hand times and electronic times in trial 1 (−0.32 ± 0.08 seconds) were not significantly different from the difference between hand times and electronic times for trail 2 (−0.30 ± 0.05 seconds). The relationship between the 2 differences was reasonably high (ICC = 0.713). The difference between the first and second hand timed trials (0.01 ± 0.06 seconds) and electronic timing (0.03 ± 0.07 seconds) was not significant, although the consistency between the 2 was lower (ICC = 0.697). The intertrial reliabilities between the 2 hand times for each timer were consistently lower than for electronic timing (Table 3), although none of the differences between the correlations were significant.

Discussion

The present study is one of the first to document the variability between hand timing and electronic timing in college football players. It is also the first to evaluate the degree of variability among multiple individuals performing hand timing. Recently, Moore et al. (¹¹) noted a difference between the average of 3 hand timers and electronic timing of only 0.08 ± 0.16 seconds. This minor degree of difference was explained by the authors as being due to their timing procedure. Their subjects started in a two-point standing position and initiated the electronic timer by moving forward 5-15 cm, which could have given the hand timers more advanced indication of motion than is typical with football players starting from a 3-point stance. Their procedure might be similar to what some call the “second movement” technique in which the initial movement forward of the shoulders is taken as the starting signal, thus allowing the timers to start their watches closer to that of the electronic system.

More recently, Brechue et al. (⁴) found the difference between 2 hand timers and electronic timing in college football players to be −0.16 ± 0.12 seconds. Their difference was similar to the widely accepted human reaction time for a visual stimulus of 0.19 seconds (¹⁷). Because most football hand timing is initiated upon the first visual movement of the player's hand, Brechue et al. (⁴) suggested that the timing difference might be accounted for by the normal reaction delay of the timers. Because their procedures were similar to those used in the present study, it is unclear why our timers consistently had reaction times that were 50% slower. One possibility for the discrepancy between the similar procedures could be accounted for by the positioning of the finish timing gate. Cronin and Templeton (⁵) recently indicated that a lower position for the electronic finish gate (60 cm) produced significantly faster times by 0.07 seconds than a higher gate (80 cm). Our gate height of 70 cm opens the possibility that the player's legs might have stopped the electronic timer before the hand timers' perception of the torso crossing the finish line. Adjusting our hand times for the difference noted by Cronin and Templeton would have produced a difference between hand times and electronic times of −0.24 ± 0.07 seconds, which would be identical to the difference noted by the NCAA for track sprints (¹³).

With the obvious importance placed on the 40-yd dash for identifying football talent (^9,16,18), it is surprising that there is no more emphasis placed on the standardization of the methodology used to secure times for it. Although it may be more convenient to use hand timing to evaluate the speed of football players, such an approach might introduce another confounding element in the estimation of player potential. Yet coaches, scouts, the media, and the public have become so aware of 40-yd times that the “slower” electronic times might not be acceptable as representing a player's “true” speed (⁸). This perception has prompted the National Football League (NFL) Combine to time their players with a manual start and an electronic finish. The starter stands approximately 10 yd from the start and activates the timing system on the initial movement of the player. This approach allows the largest component for potential error, that is, human reaction time, to remain and thus reduce the time recorded for the player's performance.

Previous work has shown that variation in attire (shorts vs. game uniform) and running surface (synthetic track vs. natural grass turf) also may significantly affect 40 yd sprint times (³). The introduction of the additional inconsistency of hand timing might add to the variability in sprint time. It would seem that those involved with the sport of football would want to standardize all aspects of sprint timing for equitable comparison among the players.

It was interesting to note the difference in ranking of the current players based on the 2 timing techniques. Despite a high rank-order correlation between the team ranking by hand timing and by electronic timing (rho = 0.97), 26 players would have had better ranking when timed by hand, 24 would have had a worse ranking, and 9 would have been ranked the same. Ranking of individual players among different teams or against accepted standards for playing positions would not be possible due to the many confounding factors previously mentioned. Granted the NFL Combine approach of having all players perform under identical circumstances is an attempt to nullify many of these extraneous variables; however, players at all levels do not have such an opportunity.

If hand timing is the only method to be used in evaluating speed among football players, several basic measurement strategies might minimize problems with this method. When 40 yd sprint timing is a regular part of the evaluation program, the same timers should be used in an attempt to increase the interrater reliability of the measurement. Timers should be consistent in their timing position, preferably perpendicular to the finish line. Obviously, the timers should be proficient in the use of a stopwatch and should learn the characteristics of the watch they use (i.e., stiffness of the start button and degree of depression needed to activate the watch). Timing initiation should always be with the index finger and never with the thumb. Despite applying all these suggestions, variations among hand timers and between hand and electronic timing are likely to occur. Using the average of several timers might help control some of this variation.

Practical Applications

Because of the critical judgments made in football based on running speed, several hundredths of a second could mean the difference between being recruited to a college team, selected by a professional team (¹⁶), or receiving a higher professional salary (⁹). Therefore, timing precision is essential and for greatest accuracy should be achieved using automated apparatus. An electronic timing system would reduce the confounding variations introduced by hand timing and provide more consistent comparisons among players. The NCAA no longer recognizes hand timing for track sprints shorter than 400 m; perhaps, the same approach should be applied to football if so much credence is to be given to the 40-yd dash for identifying player potential. Although the nature of sprint timing in football may not appear to be as critical as in track competition, the evaluation of talent for team selection and starting positions could be as essential (^6,16). Consistency of conditions (i.e., dress, running surface, and timing) could go a long way in standardizing this aspect of talent identification.

References