Introduction
Resistance training has been shown to increase strength and on-field athletic performance (17). Although coaches and researchers debate the best periodized training protocol, most agree that planned changes in training load and volume throughout the year are necessary for optimal muscular adaptation, decreased risk of injury, and avoidance of overtraining (15,17,28,29). Excessive volume load (volume × intensity), concurrent with sport practice can lead to fatigue, thereby decreasing performance (13,15,29). Although coaches can easily quantify a team's external training load, it may not consider the relative physiological stress of each individual and their resulting neuromuscular adaptation. To more accurately monitor the individual volume load, maximize physiological adaptations, and prevent overtraining on an individual basis, measures of internal training load (ITL), fatigue, and readiness need to be considered (18).
Previous studies have investigated questionnaires, rate of perceived exertion, blood-borne markers, heart rate, and vertical jump (VJ) in attempts to quantify ITL after exercise (1,3,11,18,25,28,31,32). However, very few studies have investigated proactively quantifying fatigue to measure athlete readiness and modify load accordingly. Surveys and questionnaire-based monitoring are the simplest to administer after workouts, but are subjective by nature, and thus susceptible to bias (18). Heart rate measurements are one of the most common methods to determine volume load, but come at a high monetary cost and require the availability of qualified staff, and their usefulness for high-intensity training has been previously questioned (1,3,14,18). Blood-borne markers are difficult to administer being exhaustive, time-consuming, and invasive (3,14,31).
Both immediate and chronic neuromuscular postexercise fatigue have been previously associated with VJ (1,16,24,30,32). Fatiguing the knee extensor group results in decreases in several variables of countermovement VJ (24). Neuromuscular function decreases have been reported up to 120 hours postmatch, whereas variables most sensitive to fatigue changes have included average flight time over consecutive jumps and the ratio of flight time to contraction time (time from movement initiation to the moment athlete leaves the ground) (8,24). Most research focused on VJ performance and fatigue has been post-match-play; while very little has been conducted on VJ as an assessment of fatigue and daily readiness (1,31). The ability to assess neuromuscular fatigue before exercise could help monitor the workload accumulated from previous bouts of exercise and physiological state, thereby allowing a coach to modify volume loads proactively. Therefore, the purpose of this study was to determine the sensitivity of VJ as a measure of readiness and fatigue on a daily sessional basis.
Methods
Experimental Approach to the Problem
This study used a repeated-measures within-subject design to determine the relationship between VJ performance and repetitions performed between workouts while controlling external load. Subjects performed VJ baseline testing and load calculation on day 1, followed by 2 identically loaded workout sessions where they performed multiple sets of lower-body exercises for repetitions to failure (REF). The VJ and questionnaire were measured before and after both workouts to determine sensitivity to readiness and fatigue.
Subjects
Seventeen healthy resistance-trained subjects (men n = 10; mass = 91.60 ± 13.24 kg; height = 179.70 ± 9.23 cm; age = 25.40 ± 1.51 years) (women n = 7; mass = 65.36 ± 12.29 kg; height = 162.36 ± 5.75 cm; age = 25.00 ± 2.71 years) volunteered to participate. All subjects had consistently resistance trained for at least 3 years, having experience with weight-lifting movements, squats, and deadlifts. They were between 18 and 30 years old and were free from any injury in the past 6 months. They were instructed not to perform any outside exercise 24 hours before each visit and signed a written informed consent approved by the university's institutional review board before data collection.
Procedures
Day 1: Familiarization, Baseline Testing, and Training Protocol
On arrival, subjects read and signed an informed consent document. Body mass and height were obtained using an electronic scale (ES200L; Ohaus Corp., Pinebrook, NJ, USA) and electronic stadiometer (Seca, Ontario, CA, USA). They completed the Brief Assessment of Mood questionnaire (BAM) that comprised 24 questions referring to their fatigue and soreness levels. They then performed a dynamic warm-up consisting of walking reverse lunges, walking knee hugs, Frankenstein's, and hamstring pulls for 10 m. After warm-up, they stood still on a force plate, kept their hands on their hips, then descended to a self-selected depth before jumping up as high as possible. They were measured on a force plate sampling at 1,000 Hz (AMTI, Watertown, MA, USA) and jumps were analyzed using custom LabVIEW software (version 2013; National Instruments, Austin, TX, USA). They performed 2 maximum trials, but if they continued to jump higher, more trials were recorded until jump height stabilized. The average of the 2 best jumps was used for analysis. Reliability for VJ height was an intraclass correlation coefficient of 0.92.
Subjects then completed load calculation by performing hang cleans (HCs) for 2 or 3 sets to find their 5 repetition maximum (RM). The push press (PP) was performed next for 2 or 3 sets to find their 6RM. Three-minute rest was given between sets for both exercises. High-bar back squats (BSs), Romanian deadlifts (RDL), and leg press (LP) were performed for 2 or 3 sets to find their 6RM, with 3-minute rest between all sets. All RMs were then used to calculate their estimated 1RM. Hang cleans and PP loads were 85% for all sets for both subsequent workouts, whereas BS, RDL, and LP loads were 80% for all sets.
Days 2 and 3
Subjects again filled out the BAM questionnaire, performed the same warm-up from day 1, and were reassessed for VJ performance, with the same protocol as day 1. They then completed the training protocol using the load calculations from day 1. The training protocol was designed to be a fatiguing whole-body program focusing on the hip, knee, and ankle joints. They performed HC for 4 sets of 5 repetitions followed by PP for 4 sets of 6 repetitions at 85% of their estimated 1RM with 2-minute rest between sets. Both the HC and PP exercises were performed for constant volume to insure that sufficient fatigue was achieved. Back squat, RDL, and LP were performed in succession for 4 sets to failure, with 1-minute rest between all sets, and 2-minute rest between exercises. Back squat, RDL, LP and total repetitions performed were used for analysis. Immediately after the training protocol, participants again completed the BAM questionnaire, quickly followed by a second VJ assessment, identical to the pretest. Days 2 and 3 were performed in succession, 48 hours apart, with no outside workouts or recovery methods between sessions. Dependent variables analyzed were BS volume, RDL volume, LP volume, total volume, VJ peak power (PPO), and VJ height.
Statistical Analyses
A 2 × 3 analysis of variance (ANOVA) (workout × exercise) evaluated BS, RDL, and LP volumes. A dependent t-test evaluated RTFs total volume between workouts 1 and 2. Separate 2 × 4 (sex × time) mixed factor ANOVAs evaluated VJ height and PPO. A bivariate Pearson's correlation determined the relationship between decrements in VJ performance between pre-workout 1 and pre-workout 2 and decrements in volume between workouts 1 and 2. An alpha level of 0.05 was used to determine statistical significance.
Results
For BS, RDL, and LP volumes, there was a significant (p ≤ 0.05) interaction. Back squat and LP volumes were significantly greater for workout 1 compared with workout 2, although RDL volume was not different (Table 1). For total volume, workout 1 was significantly greater than workout 2 (Table 1).
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Table 1.: Vertical jump (VJ) height, exercise volumes, and decrements (absolute and percent) of repetitions to failure for back squat (BS), Romanian deadlift (RDL), leg press (LP), and total volume (TV) between workouts 1 and 2.
For VJ height, there was no interaction but there were significant (p ≤ 0.05) main effects for sex and time. Males (32.5 ± 7.02 cm) were significantly greater than females (24.13 ± 8.39 cm). Pre-workout 1 was significantly greater than all other timepoints. Post-workout 1 and pre-workout 2 were not different, but were both significantly greater than post-workout 2 (Figure 1).
Figure 1.: Vertical jump height across timepoints.
Back squat volume decrement was significantly (p ≤ 0.05) correlated with VJ height decrement (r = 0.65) and VJ PPO decrement (r = 0.55). Vertical jump height decrement was not correlated with RDL volume decrement (r = −0.39), LP volume decrement (r = −0.04), or total volume decrement (r = 0.13). Vertical jump PPO decrement was not correlated with RDL volume decrement (r = −0.21), LP volume decrement (r = 0.08), or total volume decrement (r = 0.26).
For VJ PPO, there was no interaction but there were significant (p ≤ 0.05) main effects for sex and time. Males (3,762.23 ± 670.82 W) were significantly greater than females (2,209.55 ± 257.06 W). Pre-workout 1 was significantly greater than all other timepoints. Pre-workout 2 was significantly greater than post-workout 2 (Figure 2).
Figure 2.: Vertical jump peak power across timepoints.
For the BAM questionnaire scores, fatigue showed no interaction or main effect for sex, but there was a significant (p ≤ 0.05) main effect for time. Pre-workout 1 (2.82 ± 2.01 pts) was significantly less than every other timepoint. Post-workout 1 (9.94 ± 2.99 pts) was significantly greater than pre-workout 2 (5.06 ± 3.38 pts). Post-workout 2 (9.53 ± 3.24 pts) was greater than pre-workout 2.
Discussion
The purpose of this study was to determine the sensitivity of VJ to proactively monitor readiness and fatigue following a hypertrophy-type workout before a similar subsequent workout. The major findings were that VJ height decreased after workout and remained 8% less than baseline 48 hours later at the beginning of a second workout, declining even more after the second workout. Kamandulis et al. (19) found similar VJ height decrements after 70 drop jumps, which remained 7% less after 48 hours The current study also found that VJ height decrement was significantly correlated with BS total volume decrement, but not with any other exercise. There was a ∼2.5 cm decrement in VJ associated with a ∼5.5 repetition decrement in BS volume. This is most likely due to VJ and BS exercises sharing similar movement patterns, both requiring whole-body stabilization and primary utilization of the hip, knee, and ankle extensors compared with the other exercises (24). Although HC also uses triple extension of the lower body, this exercise was held to a constant volume to ensure that a sufficient fatigue level was achieved, but not used in the correlational analysis.
Athletes respond individually to resistance training loads and volume based on their relative physiological stress, psychological stress, and training status, affecting their overall neurological function and readiness. Claudino et al. (6) proactively regulated training load during a plyometric training study based on sessional VJ performance. They had training groups, which consisted of a regulation group where volume was adjusted based on their daily VJ performance, a nonregulation group where no volume adjustment was made, and a yoked group where adjustment was based off matched participants from the regulation group. Vertical jump displayed improvements in all 3 training groups but resulted in greater volume over the 6 weeks for the nonregulation group, whereas the regulation group had decreased total volume without affecting performance gains. The current study used the same concept, using VJ as a monitoring tool, but in contrast to Claudino, we measured the volume of a subsequent workout finding a significant relationship between decrements in VJ height and BS volume. The ability of VJ height as a sensitive measure of readiness may be explained by the bimodality of the stretch-shortening cycle (SSC) mechanism. Reductions in SSC performance happen immediately during exercise, recovering approximately 2 hours after exercise and demonstrate a secondary reduction 2 days after exercise when muscle damage is the greatest (22). Therefore, the current study demonstrates that measuring VJ height after a fatiguing workout and before a subsequent workout may be a beneficial tool for monitoring readiness to train.
Neuromuscular fatigue can be broken into 2 main parts: a neurological decrease in function and muscular failure (7,24,30). A decrease in performance from either can affect resistance training workout quality, effectiveness, or on-field performance. This study is consistent with other investigations finding VJ performance decreased after exercise, however, most studies focused on post-match play rather than resistance training (5,9,10,20,21,32). West et al. (34) examined neuromuscular function after a competitive rugby match, and found VJ PP decreased by approximately 7% at 12 and 36 hours after match, but returned to resting levels 60 hours after match. Similarly, the current study found decreases of 4.6% in PP 48 hours after exercise. McLellan et al. (21) measured fatigue during a single rugby match finding VJ PP and RFD were reduced 30 minutes and 24 hours after match, but returned to pre-match levels 48 hours after match. The current study demonstrated that PP decreased immediately after exercise and 30 minutes after exercise, but unlike McLellan, found that it remained low 48 hours after exercise. This difference between studies could be due to movement pattern and central nervous system requirements. The BS is a preplanned exercise solely occurring in the sagittal plane, primarily using ankle, knee, and hip extensors (12,33). In contrast, rugby requires decision making and central nervous system activity, navigating through all 3 planes during tackling, sprinting, scrummaging, and reactive agility (2,23,26). Consequently, the current study indicates that differences in isolated muscular fatigue and general central nervous system fatigue can result in dissimilar recovery times of VJ performance.
Strength coaches monitor training in attempts to quantify ITL, reduce risk of injury, and optimize performance. However, muscular fatigue affects the ability to voluntarily activate muscle fibers, resulting in a decrease in maximum voluntary strength, power, and work capacity (10,27,34). Ciccone et al. (4) found that 60% of subjects exhibited fewer fourth-set repetitions and less average power across BS sets in fatiguing alternating sets, when compared with a traditional resistance training program. Similarly, the current study displayed fewer repetitions for BS, LP, and lower total volume of a second workout after a fatiguing workout. Vertical jump height decreased 13% immediately after and remained approximately 9% lower 48 hours later, whereas VJ PP displayed a 5% decrease, showing that fatigue was still prominent 2 days later. Rodacki et al. (24) found comparable decreases of 14% in VJ performance immediately after fatiguing the knee extensors, with no significant change in the knee flexors. Consistent with previous literature, the current study indicates that VJ performance can be sensitive to proactively monitor training and possibly prevent performance decreases.
In summary, VJ performance decrement was correlated with BS volume, but no other exercise. Back squat shares movement specificity with VJ, both requiring triple extension of ankle, knee, and hip joints in the sagittal plane (24). Other squat variations may also demonstrate similar fatigue sensitivity when proactively monitored by VJ considering shared kinematic factors. Hang cleans and PP exercises were executed to guarantee adequate fatigue level, and thus the application of VJ to measure fatigue from those exercises is beyond the scope of this study. Further research is needed to investigate VJ as a monitoring tool for other exercises.
Practical Applications
The findings of this study demonstrate a significant relationship between decrements in VJ height and BS volume after a fatiguing workout. An ∼2.5 cm decrease in VJ height resulted in an ∼5.5 repetition decrease in BS volume. Therefore, strength coaches could use pre-VJ height assessment as a tool to measure readiness for BS training after high volume, fatiguing resistance training bouts that include triple extension patterns.
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