Neuromuscular, Hormonal, and Metabolic Responses to Different Plyometric Training Volumes in Rugby Players

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DOI: 10.1519/JSC.0b013e31828c32de · Source: PubMed
Abstract
The purpose of this study was to investigate the effect of different volumes of plyometric exercise (i.e., 100, 200, or 300 hurdle jumps) on acute strength and jump performance as well as on the acute hormonal and lactate responses in rugby players. Eleven young male elite rugby players (age, 23.5 ± 0.9 years; height, 173 ± 4.8 cm) volunteered for the study. Maximal isometric peak torque (PT), maximal rate of force development (RFD), and squat jump (SJ) and drop jump (DP) performance were assessed before and 5 minutes, 8 hours, and 24 hours after 100, 200, or 300 jumps. In addition, total testosterone, cortisol, and lactate were measure before and after the three different plyometric exercise volumes. There were significant decreases in the PT (P<0.02) and maximal RFD (P<0.001) 5 minutes, 8 hours, and 24 hours after 100, 200 and 300 jumps, with no differences between the exercise volumes. Additionally, there were significant decreases in the SJ (P<0.001) and DJ (P<0.01) performances 24 hours after 100, 200, and 300 jumps, with no differences between the exercise volumes. However, there were significant increases in the total testosterone (P<0.001), cortisol (P<0.05), and lactate (P<0.001) after 100, 200, and 300 jumps, with no differences between the exercise volumes. All plyometric exercise volumes (100, 200, and 300 jumps) resulted in similar neuromuscular, metabolic, and hormonal responses.
NEUROMUSCULAR,HORMONAL, AND METABOLIC
RESPONSES TO DIFFERENT PLYOMETRIC TRAINING
VOLUMES IN RUGBY PLAYERS
EDUARDO L. CADORE,
1,2
ERALDO PINHEIRO,
1
MIKEL IZQUIERDO,
2
CLEITON S. CORREA,
1
RE
´
GIS RADAELLI,
1
JOCELITO B. MARTINS,
1
FRANCISCO L. R. LHULLIER,
1
ORLANDO LAITANO,
3
MARCELO CARDOSO,
1
AND RONEI S. PINTO
1
1
Exercise Research Laboratory, Physical Education School, Federal University of Rio Grande do Sul, Porto Alegre, Brazil;
2
Department of Health Sciences, University of Navarra, Tudela, Spain; and
3
Department of Physical Education, Federal University of
Vale do Sa˜o Francisco, Petrolina, Brazil
A
BSTRACT
Cadore, EL, Pinheiro, E, Izquierdo, M, Correa, CS, Radaelli,
R,Martins,JB,Lhullier,FLR,Laitano,O,Cardoso,M,
and Pinto, RS. Neuromuscular, hormonal, and metabolic
responses to different plyometric training volumes in rugby
players. J Strength Cond Res 27(11): 3001–3010, 2013—
The purpose of this study was to investigate the effect of
different volumes of plyometric exercise (i.e., 100, 200, or
300 hurdle jumps) on acute strength and jump performance
and on the acute h ormonal and lactate responses in rugby
players. Eleven young male elite rugby p layers (age, 23.5 6
0.9 years; height, 173 6 4.8 cm) volunteered for the study.
Maximal isometric peak torq ue (PT), maximal rate of force
development (RF D), squat ju mp (SJ), and dr op jump (DJ)
performance were assessed before and 5 minutes, 8 hours,
and 24 hours after 100, 200, or 300 jumps. In addition, t otal
testosterone (TT), cortisol (COR), and lactate were mea-
sured before and after the 3 different plyometric exercise
volumes. There were significant decreases in the PT (p ,
0.02) and maximal RFD (p , 0.001) 5 minutes, 8 hours, and
24 hours after 100, 200, and 300 jumps, with no differences
between the exercise volumes. Additionally, there were
significant decreases in the SJ (p , 0.001) and DJ (p ,
0.01) performances 24 hours after 100, 200, and 300 jumps,
with no differences between the exercise volumes. However,
there were significant increases in the TT (p , 0.001), COR
(p , 0.05), and lacta te (p , 0.001) after 100, 200, and
300 jumps, with no differences between the exercise volumes.
All plyometric exercise volumes (100, 200, and 300 jumps)
resulted i n similar neuromuscular, metabo lic, and hormonal
responses.
KEY WORDS rate of force development, maximal strength,
testosterone, cortisol, jump performance
INTRODUCTION
R
ugby is a very strenuous sport that places an
emphasis on jumping, running speed, and ball
throwing. In addition, rugby requires substantial
maximal strength levels to be able to hit, block,
push, and hold during game actions. High levels of maximal
strength and muscle power output and a high aerobic capacity
are required to perform these actions and to successfully par-
ticipate in elite rugby leagues (25,28). Given the relevance of
power development in rugby, plyometric training is widely
performed during the physical training of rugby players,
mainly because of the influence of this type of training on
power, jump, and sprint performance (16). However, the influ-
ence of the amount of jumping during training on neuromus-
cular recovery has been poorly investigated. Several studies
have shown that plyometric training improves strength
(23,36,39), power (6,9), jump height (6,8,23,36,39), and sprint
performance (6,36). Furthermore, the plyometric training vol-
ume has been shown to possibly influence the development of
speed, jump height, and power gains normally induced by train-
ing (36,38). In a study by Villarreal et al. (36), a low volume (i.e.,
420 jumps per week) of plyometric training was found to be
a sufficient stimulus to promote speed increases when compared
with moderate (i.e., 840 jumps per week) and high plyometric
training volumes (i.e., 1,680 jumps per week). However, the
same was not observed in the jump height performance, in
which only moderate and high volumes promoted improve-
ments after 12 weeks of training (36). However, to the best of
our knowledge, no previous studies have investigated the acute
effects of different plyometric exercise volumes on strength and
power recovery . Understanding the influence of different vol-
umes of plyometric exercise on strength and power output
Address correspondence to Dr. Eduardo L. Cadore, edcadore@
yahoo.com.br.
27(11)/3001–3010
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recovery could help coaches to monitor and optimize recovery
time between physical and technical training sessions.
Strength training volume has a strong influence on the acute
hormonal responses to strength training (4,10 ,18, 34). In addi-
tion, several studies sugges t that the hormonal response to
individual training sessions is related to the magnitude of
chronic neuromuscular adaptatio ns to strength training
(4,12,19,30). In a study by Hansen et al. (12), young subjects
performing a strength training session that stimulated acute
elevations in testosterone (i.e., arm + leg exercises = greater
muscle mass involved) had greater strength gains in their arms
than did another group that performed a strength training
sessiondesignedtonotstimulateanacutetestosterone
response (i.e., only arm exercises = less muscle mass involved).
In a similar study, Ronnestad et al. (30) showed that greater
strength gains and hypertrophy occurred in young men who
performed strength training composed of sessions that elicited
acute hormonal elevations. In contrast, West et al. (40) showed
that the exposure of loaded muscle to exercise-induced el eva-
tions in endogenous anabolic hormones does not enhance
strength training adaptations. However, the o rder of the exer-
cises performed in that study may explain these results because
the exercise that was supposed to acutely elevate the serum
hormones (i.e., the leg exercise) was per formed after the exer-
cise for the investigated muscle (elbow flexors). In a study by
Ronnestad et al. (30), the exercise order was reversed, that is,
the legs (greater muscle mass involved and, consequently,
greater stimulus to the hormone elevation) were exercised first,
and therefore, the elbow flexor exercises were performed dur-
ing the period when the hormone levels were elevated. W ith
this appr oach, Ronnestad et al. (30) observed greater strength
training adaptatio ns induced by the training proto col that eli-
cited greater acute hormonal elevations. T hus, to determine
themainfactorsrelatedtostrengthtrainingsessionsthat
greatly influence acute testosterone responses, it is important
to create an anabolic hormonal response and optimize the
neuromuscular adaptations to training. Although strength
training volume has a critical influence on the magnitude
and duration of the acute response of testosterone and cortisol
(COR [10,34]), to the best of our knowledge, there are no data
available regarding the influence of plyometric training volume
on the acute responses o f testostero ne and COR.
A knowledge of the neuromuscular slope recovery after
different plyometric exercise volumes is very important for
helping coaches monitor and periodize the p hysical
training of elite athletes. Thus, given the lack of informa-
tion regarding neuromuscular recovery and the acute
hormonal r esponses to different plyometric training vol-
umes, we investigated the effect of different volumes of
plyometric training (i.e., 100, 200, or 300 hurdle jumps) on
strength and jump performance and on the acute hor-
monal and lactate responses in rugby players. Our hypoth-
esis was that greater exercise volumes would result in
a greater decrease i n strength and jump performance after
exercise. Second, we hypothesized that greater exercise
volumes would result in larger responses of testosterone,
COR, and lactate.
METHODS
Experimental Approach to the Problem
To investigate the effect of exercise volume on the acute
neuromuscular, metabolic, and hormonal responses to
plyometric exercise, the subjects came to the labo ratory
on 4 different occasions. On the first day, the subjects
signed a written consent form, and their anthropometric
characteristics were evaluated. On the last 3 days, the
plyometric exercise protocols (i.e., 100, 200, and 300 jumps)
were performed in random order, with 1 week of rest
between each protocol. All the subjects c ompleted the 3
plyometric exercise protocols, and the subjects performed
each session individually. It has been shown that only 100
jumps are necessary to elicit important acute neuromuscu-
lar r esponses, such as maximal voluntary force and evoked
force declines (33). Howe ver, we cho se to investigate exer-
cise volumes .100 jumps per session because these plyo-
metric exercise vo lumes have been extensively used in this
research area and in the training routines of high-level ath-
letes (36 –38). Before and after (5 minutes, 8 hours, and
24 hours ) each jumping volume, the subjects performed
strength and jumps tests. In addition, before and immedi-
ately after each jumping volum e, the subjects had their
blood drawn to measure serum hormone and lactate levels.
We had previously tested the stability and reliability of all
variables with the same population before the study. All the
subjects performed all the plyometric exercise protocols at
thesametimeoftheday(between8and9
AM)throughout
the study period. The ambient conditions were kept con-
stant during all tests (temperature: 22–248 C).
Subjects
Eleven young male national level rugby players (Mean 6 SD:
23.5 6 0.9 years), who were engaged in regular and systematic
physical and technical training program for at least 3 years
(6 times a week), volunteered for the study after completing an
ethical consent form and signing an informed consent docu-
ment. The subjects were carefully informed about the design
of the study with special information given regarding the pos-
sible risks and discomfort related to the procedures. Ethics
Committee of Federal University of Rio Grande do Sul
approved the study in accordance with the Helsinki Declara-
tion. Exclusion criteria included any history of neuromuscular,
metabolic, and hormonal diseases. The subjects were not
taking any medication with influence on hormonal and neu-
romuscular metabolism and were advised to maintain their
normal dietary intake throughout the study. The physical
characteristics of the subjects are shown in Table 1. Body mass
and height were measured using an Asimed analog scale
(resolution of 0.1 kg) and an Asimed stadiometer (resolution
of 1 mm), respectively . Body composition was assessed using
the skinfold technique. A 7-site skinfold equation was used to
Physiological Responses to Plyometric Exercise
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estimate body density (15), and body fat was subsequently
calculated using the Siri equation (32).
T he training routine of the subjects consisted of 3–4 sessions
per week of rugby (specific physical work, technical, and
tactical actions) and 3 strength training sessions per week.
In the period of study, the subjects had been training 5 sets
of 100 hurdle jumps, with 5 minutes of rest between sets. The
subjects had been performing plyometric training routine at
least 2 years before the study. However, during the data
collection (;5 weeks), no plyometric exercise session was
performed by the subjects. In addition, these subjects were
in the second place in the Brazil Cup immediately before the
study and recently had started their period out of season,
which avoided the influence of their training sessions in the
study protocols.
Maximal Voluntary Contraction and Rate of
Force Development
Maximal isometric peak torque (PT) and rate of force
development (RFD) were obtained using an isokinetic
dynamometer (Humac, CSMI, Stoughton, MA, USA) imme -
diately before (pre), 5 minutes after (post), 8 hours after (8
hours post), and 24 hours after (24 hours post) the exercise
protocols. The subjects were positioned seated with their
hips and thighs firmly strapped to the seat of the dynamom-
eter, with the hip angle at 858. After that, the subjects
warmed up for 10 knee extension and flexion repetitions at
an angular velocity of 908$s
21
, performing a submaximal
effort. After having their right leg positioned by the evalua-
tors at an angle of 1208 in the knee extension (1808 repre-
sented the full extension), the subjects were instructed to
exert the maximum strength as fast as was possible when
extending or flexing the right knee. All the subjects were very
much familiarized with the isometric test protocol. Before
the plyometric exercise protocols, and after 8 and 24 hours,
the subjects had 2 attempts at obtaining the maximum vol-
untary contraction (MVC) of the knee extensors, each lasting
5 seconds. Immediately after (post) the exercise protocols,
the subjects made 1 attempt to perform the MVC. The rest
interval between each attempt of the protocol was 2 minutes.
During all the maximum tests, the researchers provided ver-
bal encouragement so that the subjects would feel motivated
to produce their maximum force. The force-time curve was
obtained using Humac software, with an acquisition rate of
2,000 Hz. Maximal PT was
defined as the highest value of
the torque (newton meter) re-
corded during the unilateral
knee extension. The isometric
force-time analysis on the
absolute scale included the
maximal RFD (newtons per
second), defined as the greatest
increase in the force in time.
T he RFD was derived as the
average slope of the moment-
time curve (Δmoment/Δtime)
over time intervals of 50 millisec-
onds relative to the onset of con-
traction, which was considered
the point that the torque ex-
ceeded 7.5 N$m(1),andwere
determined using the Excel soft-
ware. The test-retest reliability
coefficients (intraclass correlation
coefficient [ICC]) were .0.94
for all the variables in the isomet-
ric protocol.
TABLE 1. Physical characteristics, strength, and
jump performance.*
Mean 6 SD
Age (y) 22.4 6 2.8
Height (cm) 173.0 6 4.8
Body mass (kg) 81.2 6 8.3
Fat mass (%) 11.6 6 1.8
KE peak torque (N$m) 346.8 6 48.4
KE RFD (N$m$s
21
) 325.3 6 118.6
Squat jump (cm) 36.2 6 3.0
Drop jump (cm) 37.3 6 3.2
*KE = knee extensors; RFD = rate of force develop-
ment.
Figure 1. Squat jump height (centim eters; mean 6 SD) before; 5 minutes post; 8 hours post; and 24 hours post
100, 200, and 300 jumps. *Significant time effect (p , 0.001).
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Jumping Performance
After the MV C assessment (pre, immediately post, 8 hours post,
and 24 hours postplyometric exercise protocols), the subjects
performed a jump test using an electronic contact mat system
(Jumptest, Hidrofit, Belo Horizonte, Brazil). Jump height was
determined using an acknowledged flight-time calculation (3)
and the software Miltsprint. Each subject was instructed to per-
form with maximum effort dur-
ing the double-leg squat jump
(SJ)anddropjump(DJ)tests.
T hey were given 3 attempts to
obtain their maximum jump
height in each test, with 30 sec-
onds of rest between attempts.
All the subjects were very famil-
iar with the jump test protocol.
During the SJ test, the subjects
were instructed to start the jump
with their knees at a 908 angle
and to avoid any countermove-
ment.DuringtheDJtest,the
subjects started the test on
a 40-cm block because in the pre-
vious trial, all the participants
had their best DJ performance
from this height (30, 40, and 60
cm were tested). T hey were in-
structed to jump for maximal
height and minimal contact time.
T he subjects were again in-
structed to leave the electronic
contact mat system with their
knees and ankles fully extended
andtolandinasimilarlyextendedpositiontoensurethevalidity
of the test. Four basic techniques were stressed: (a) correct
posture (i.e., spine erect, shoulders back) and body alignment
(e.g., chest over knees) throughout the jump; (b) jumping
straight up with no excessive side-to-side or forward-backward
movement; (c) soft landing, including toe-to-toe heel rocking
and bent knees; and (d) instant recoil preparation for the next
jump (36). When perform-
ing the jumps, all the sub-
jects held their hands on
their hips. The test-
retest reliability coefficients
(ICCs) were 0.87 for the SJ
test and 0.93 for the DJ test.
Blood Collection
and Analysis
Blood was obtained
between 8 and 9
AM, after
8 hours of sleep, 12 hours
of fasting an d 2 days with
no physical training ses-
sion. The t ime of blood
collection was chosen
because of its use in
many studies conducted
with these procedures
for the control of the cir-
cadian hormonal range
Figure 2. Drop jump height (centimeters; mean 6 SD) before; 5 minutes post; 8 hours post; and 24 hours post
100, 200, and 300 jumps. Please, note that the drop jump height mean after 24 hours post 100 jumps is under the
values post 300 jumps. *Significant time effect (p , 0.01).
Figure 3. Peak torque (newton meter; mean 6 SD) before; 5 minutes post; 8 hours post; and 24 hours post 100, 200,
and 300 jumps. *Significant time effect (p , 0.02).
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(29,36,37). The subjects sat in a slightly rec lined pos ition
during 15 minutes, and, after that, 10 ml of blood was
drawn from the antecubital vein before, and 3
minutes after the plyometric e xercise protocols with similar
techniques. After collection,
the blood was maintained in
ambient temperature for
45 minutes and then centri-
fuged f or 10 minutes at 2,000
rpm, and serum was removed
and frozen at 2208 Cforlater
analysis. With this blood s am-
ple, c oncentrations of total
testosterone (TT) (nanograms
per milliliter) and COR (milli-
grams per deciliter; MP BioMed-
icals, T winsburg, OH, USA) were
determined in duplicate, using
radioimmunoassay kits. From
these values, it was possible to cal-
culate the TT/COR ratio. To
eliminate interassay variance, all
the samples were analyzed within
thesameassaybatch,andallin-
traassay variances were #6.3%.
Antibody sensitiviti es were 0.7
nmol$L
21
for TT, and 1.4
nmol$L
21
for COR. The test-re-
test reliability coefficients (ICC)
were 0.85 to COR, 0.94 to TT.
Lactate Determination
Capillary blood lactate samples were obtained from a hyperemic
earlobe. After cleaning and puncturing, a 5-ml sampl e was
drawn. Lactate accumulation was determined before and 3 mi-
nutes after the plyometric exer-
cise protocols through the
enzymatic reaction technique
by using a portable lactimeter
(Accutrend Lactate). The test-re-
test reliab ility coefficient (ICC)
was 0.8 7.
Plyometric Exercise Protocols
Plyometric exercise protocols
(i.e., 100, 200, or 300 jumps)
were performed in a random
order, with 1 week of rest
between each protocol. First,
the s ubjects performed a stan-
dardized 3-minute dynamic
warm-up consisting of high-
knees, lunges, abdominal exer-
cises, side shuffles, and power
skips. The warm-up was care-
fully monitored during each
session to ensure that each
session was performed in the
exact same fashion. The subjects
performed sets of 100 hurdle
Figure 4. Maximal rate of force development (newton meter per second; mean 6 SD) before; 5 minutes post; 8
hours post; and 24 hours post 100, 200, and 300 jumps. *Significant time effect (p , 0.001).
Figure 5. Total testosterone concentrations (nanograms per milliliter; mean 6 SD) before and immediately after
100, 200, and 300 jumps. *Significant time effect (p , 0.001).
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jumps with 10 seconds of active rest between each repetition of
10 jumps (i.e., return to the first hurdle using low-intensity
running). During the protocols with greater exercise volumes (i.
e., 200 and 300), the rest intervals between sets were passive
and lasted for 5 minutes. T he hurdles were positioned with an
approximately 45-cm distance between each hurdle. All the
hurdles had a height of 40 cm because in the previous trial, all
the subjects had shown their
best DJ performance when
jumping from this height (30,
40, 50, and 60 cm were tested).
Statistical Analyses
Results are reported as mean 6
SD. Comparisons between dif-
ferent plyometric exercise proto-
cols were assessed using a 2-way
analysis of variance with
repeated measures (volume 3
time). When a significant F
value was achieved, least signif-
icant difference post hoc proce-
dureswereusedtolocatethe
pair wise differences. The sam-
ple size was calculated using the
GPOWER program (version
3.0.1), which determined a sam-
ple of n = 11 subjects, with a sta-
tistical power of .85% in all
variables. The retrospective sta-
tistical power provided by SPSS
after analysis was .0.95 in all variables in which a significant
time effect was observed. Significance was accepted when
p # 0.05.
RESULTS
At baseline, no significant differences were observed for all the
variables analyzed between the different treatments (i.e., 100,
200, or 300 jump interventions).
Jumping Performance
Regarding SJ performance,
there was a significant time
effect ( p , 0.001), but no pro-
tocol effect and time vs. proto-
col interaction were observed.
Post hoc analysis showed that
all plyometric exercise volumes
(100, 200, and 300 jumps) sig-
nificantly reduced the SJ per-
formance 24 hours after the
protocol (P100: 23.6 6 5.7%;
P200: 22.5 6 10.2%; P300:
24.2 6 5.7%), whereas no
changes were observed imme-
diately after or 8 hours after the
protocols (Figure 1).
Regarding the DJ perfor-
mance, there was a significant
time effect (p , 0.01), but no
protocol effect and time vs. pro-
tocol interaction were observed.
Post hoc analysis showed that
Figure 6. Cortisol concentrations (milligrams per deciliter; mean 6 SD) before and immediately after 100, 200,
and 300 jumps. *Significant time effect (p , 0.05).
Figure 7. Lactate concentrations (millimoles per liter; mean 6 SD) before and immediately after 100, 200, and
300 jumps. *Significant time effect (p , 0.001).
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all plyometric exercise volumes (100, 200, and 300 jumps)
reduced the DJ performance after 24 hours (P100: 29.0 6
5.8%; P200: 26.3 6 5.5%; P300: 24.0 6 3. 85%), whereas no
changes were obs erved im mediate ly after or 8 hours after the
protocols (Figure 2).
Strength Performance
Regarding the isometric PT, there was a significant time
effect (p , 0.02), but no protocol effect and time vs. protocol
interaction were observed. Post hoc analysis showed that the
reductions were observed immediately (P100: 213.8 6
11.3%; P200: 212.3 6 8.9%; P300: 210.1 6 20.9%), 8 hours
(P100: 212.9 6 15.2%; P200: 213.8 6 15.5%; P300: 29.8 6
22.3%), and 24 hours (P100: 217.9 6 11.9%; P200: 215.4 6
16.1%; P300: 215.0 6 17.9%) (p , 0.0 2) after all plyometric
exercise volumes (100, 200, and 300 jumps) when compared
with the preexercise values (Figure 3).
A significant time effect (p , 0.001) was also observed for the
maximal RFD; however, no protocol effect and time vs. pro-
tocol interaction were observed for this variable. Post hoc anal-
ysis showed reductions immediately (P100: 210.3 6 8.0%;
P200: 212.4 6 6.8%; P300: 216.3 6 9.7%), 8 hours (P100:
210.8 6 17.9%; P200: 210.2 6 14.8%; P300: 29.2 6 8.3%),
and 24 hours (P100: 214.9 6 35.1%; P200: 211.4 6 12.3%;
P300: 29.8 6 13.8%) (p , 0.001) after all plyometric exercise
volumes (100, 200, and 300 jumps, respectively) when com-
pared with the preexercise values (Figure 4).
Hormonal and Lactate Responses
Regarding TT values, there were significant time effects (p ,
0.001), but no protocol effect and time vs. protocol interaction
were observed. The serum TT increased after 100 (10.9 6
8.2%), 200 (27.6 6 15.3%), and 300 jumps (10.9 6 19.1%)
(Figure 5). Furthermore, there were significant time effects
for the serum COR after all exercise protocols (p , 0.05),
but no protocol effect and time vs. protocol interaction were
observed. Serum COR increased after 100 (17.4 6 50.2%), 200
(21.2 6 69.2%), and 300 jumps (42.4 6 70.9%) (Figure 6).
However, no significant time effect, protocol effect, and time
vs. group interaction were observed for the TT:COR ratio.
T here was a significant time effect on the lactate concentra-
tions (p , 0.001), but no protocol effect and time vs. protocol
interaction were observed. Increases in the lactate concentra-
tions were observed after 100 (177.0 6 114.0%), 200 (195.0 6
202.3%), and 300 jumps (178.0 6 65.1%) (Figure 7).
DISCUSSION
T he primary finding of this study was that neuromuscular
performance was impaired 24 hours after all 3 plyometric
exercise volumes (i.e., 100, 200, and 300 jumps). Furthermore,
an interesting finding was the similar acute lactate and
hormonal response s observed independent of the exercise
volume performed. Considering the present results, we
conclude that the 100-jump session is an optimal stimulus to
produce marked acute physiolog ical responses even in highly
trained athletes. W ithin the volume range tested (100—300
jumps), a greater exercise volume (300 jumps) appears to result
in the same neuromuscular impairment as the lower exercise
volumes 24 hours after exercise in rugby athletes.
Both traditional strength training (i.e., heavy load and slow
contraction velocity) and explosive strength training (i.e., light
to moderate loads and high contraction velocity) acutely
impair neuromuscular function, resulting in decreased force,
power, and RFD (14,20,21). This decreased performance may
be explained by central (20,21) and peripheral (7) mechanisms
of fatigue. Regarding stretch-shortening cycle (SSC) exercises,
it has been demonstrated that submaximal, long duration, and
exhaustive SSC exercise, such as marathon running, has an
acute deleterious effect on strength performance (26,35). How-
ever, data on the effect of explosive SSC exercises, such as
plyometric training bouts, on neuromuscular function are
scarce. In a study by Drinkwater et al. (7), 212 ground contacts
performed during a plyometric exercise session acutely
impaired strength and RFD, which were recovered after 2
hours, in physically active subjects. In another study, Skurvy-
das et al. (33) showed that only 100 jumps, continuous or
divided into 5 sets of 20 jumps, resulted in marked declines
in maximal voluntary contraction and in the evoked force . To
the best of our knowledge, no study has compared the effect of
performing different amounts of plyometric exercise on the
neuromuscular function of athletes. Our results are consistent
with those of Drinkwater et al. (7) because significant
decreases were observed in the PT and RFD immediately after
all volumes performed. A unique finding of this study was that
the PT and the RFD were not recovered at 8 or 24 hours after
plyometric exercise, even when a lower exercise volume (i.e.,
100 jumps) was performed. It should be noted that despite the
highly trained status of the rugby players, their strength per-
formance was impaired until 24 hours after exercise. F rom
a practical point of view, the results of this research indicate
that coaches should carefully monitor the volume of plyomet-
ric exercise sessions during microcycles because athletes might
not be able to perform strength or power activities at their best
within at least that first 24 hours after plyometric tra ining.
In this study, no differences in the jump height values were
observed between the preexercise, immediately postexercise,
and 8 hours postexercises. Nevertheless, all plyometric
training volumes resulted in an impaired jump performance
24 hours after exercise. A possible explanation is that the
performance immediately postexercise had the benefits of
the postactivation potentiation (PAP) phenomenon
(5,13,16,31). Indeed, it has been shown that the performance
of strength exercises before plyometric tests improves jump
performance, resulting in greater jump height, power, and
velocity (31). This response appears to be greater in type 2
muscle fibers, which are preferentially recruited during
explosive contractions (20,21). Whether the PAP phenome-
non prevented impairments in the jump performance imme-
diately after the plyometric exercise bouts remains
speculative. If true, the PAP phenomenon only prevented
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a decline in performance for tests in which the SSC was
involved because marked reduction was observed in the
MVC performance immediately after exercise.
Although jump performance was not reduced immediately
after exercise, all strength and power parameters (i.e., PT,
RFD, SJ, and DJ) were impaired 24 hours after plyometric
exercise. This impairment might be explained by the fact that
plyometric exercise can impart eccentric loads over 5 times
the subjects’ body weight on the active muscle groups (13),
resulting in a force production beyond what could be volun-
tarily produced. This eccentric overload might impair the
skeletal muscle power and strength for several days after exer-
cise because of damage of the contractile mechanisms (27).
Indeed, it has been shown that recovery after eccentric exer-
cise might consist of a full recovery immediately after exercise
with subsequent strength reductions in the subsequent days,
which can be described as a bimodal recovery of SSC exer-
cises (26).
Another interesting finding of this study was the similar
strength and power output recovery pattern after all amounts
of plyometric exercise. A possible exp lanation for these results
is the period of recovery used between sets in the longer
protocols (i.e., 5 minutes), which might have allowed the
subjects to start each subsequent set in a similar neuromuscular
condition. T hese results may have an important practical
implication because a recovery of 5 minutes might be an
optimal rest period for performing multiple sets of 100 ground
impacts. Notwithstanding, we did not compare the 5-minute
period of recovery with longer or shorter periods of recovery
between sets, and this hypothesis remains untested. In addition,
the subjects of this study were rugby athletes who often
perform plyometric training sessions of approximately 500
ground impacts, and it is possible that the same pattern of
neuromuscular responses would not be observed in untrained
subjects. Indeed, it has been shown that fatigue after resistance
exercise depends on the subject’s athletic background (11).
T hus, caution has to be exercised when interpreting our results
because it is possible that these acute neuromuscular responses
would occur only in elite rugby players who often perform
high-volume plyometric training.
Regarding the hormonal responses, the acute response to
traditional strength training has been shown to be volume
dependent because greater responses are observed as the
number of sets increases (34). However, there are few data
regarding the hormonal response to plyometric exercise. In
a study by Beaven et al. (2), small increases in salivary testos-
terone (;13%) and COR (;29%) were observed in response
to the same volume of different jump exercises (i.e., 3 sets of 3
repetitions). To the best of our knowledge, no study has inves-
tigated the effect of different volumes of plyometric training on
the testosterone and COR responses. Surprisingly, in our
study, the 3 jump volumes resulted in similar hormonal
responses. Regarding testosterone, the similar responses
between the different exercise volumes can be associated with
the similar lactate responses to these protocols. It has been
shown that the testosterone response to resistance exercise is
influenced by a direct stimulation of the testes by lactate, as
demonstrated in a study by Lu et al. (22), who observed a cor-
relation between the increase in testosterone and the increase
in lactate during an incremental protocol in rats. Furthermore,
these authors demonstrated in vitro that a direct infusion of
lactate into the testes results in a dose-dependent increase in
testosterone. Thus, it is possible that the absence of an addi-
tional increase in lactate when the exercise volume was
increased might explain the absence of an additional increase
in testosterone. Both responses might be related to the long
rest time used when 200 and 300 jumps were performed (i.e.,
5 minutes). In fact, it has been shown that lactate and testos-
terone responses are lower with long rest intervals between
sets when compared with short rest intervals (18,19,29). In
addition, explosive strength training has been shown to result
in low increases (i.e., ;10%) in the testosterone (2,24) and
lactate responses after exercise. Although testosterone responses
to resis tance exercise have been postulated as an important
factor to optimize strength and hypertrophy (4,12,19,30), the
role of this hormone in power development during plyometric
trainingneedstobeinvestigated further .
With respect to basal circulating COR levels, this catabolic
hormone is responsible for lipid and protein degradation and
the subsequent mobilization of energy substrates during
exercise (19). In addition to the metabolic impact related to
intensity, volume, and rest interval (18,29,34), it has been dem-
onstrated that training status directly influences the magnitude
of the adrenal cortical response, with trained individuals hav-
ing a significantly lower acute COR response compared with
untrained individuals (4,17). Thus, the fact that the subjects in
this study were strength trained may be another factor that
influenced the weak COR response to the exercise protocols
performed in this study.
Our study has some limitations. F irst, our results showed no
differences between acute neuromuscular, lactate, and hormonal
responses after 100, 200, or 300 hurdle jumps. However, no
training adaptations were investigated in this study, and the
potential chronic neuromuscular adaptations induced by these 3
different plyometric exercise volumes must be investigated in
a long-term study . Second, this study examined only 1 type of
plyometric exercise (i.e., hurdle jumps), which involves minimal
contact time and fast SSC, and it is not appropriate to
extrapolate these results to other types of plyometric exercises
(i.e., countermovement jump, SJ). Another possible limitation of
this study was the absence of strength and power tests after the
first 24 hours (i.e., 48 and 72 hours postexercise) because
possible differences between the plyometric exercise volumes
performed could appear if a longer recovery period was
monitored. However, this hypothesis remains speculative and
must be investigated.
In summary, the present results expand the data regarding
the acute neuromuscular effect of SSC exercise because it shows
that different plyometric exercise amounts ranging from 100 to
300 ground impacts impaired the neuromuscular performance
Physiological Responses to Plyometric Exercise
3008
Journal of Str ength and Conditioning Research
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in power-trained rugby players. In addition, these impairments
in neuromuscular performance remained until 24 hours after
plyometric exercise. Moreover, similar neuromuscular, meta-
bolic, and hormonal effects were observed after all training
volumes tested. Thus, a low volume (100 jumps) of plyometric
training seems to be a sufficient stimulus to result in marked
neuromuscular, metabolic, and hormonal acute responses, and
these responses are not enhanced for the training sessions of up
to 300 jumps. T he rest interval between sets of 100 jumps used
in this study (i.e., 5 minutes) might help to explain the lack of
differences between the results of the different exercise volumes.
PRACTICAL APPLICATIONS
The results of this study suggest that coaches should
carefully monitor the volume of plyometric training sessions
during microcycles because athletes might not be able to
perform strength or power activities at their best until 24 hours
after plyometric exercise sessions. Our results showed that the
jump height, PT, and RFD were not recovered 24 hours after
completing 100, 200, or 300 hurdle jumps. Thus, even when
only 100 ground impacts are performed, plyometric exercise
sessions must be followed by more than 24 hours of recovery
to allow rugby athletes to recover their strength and power. In
addition, if greater exercise volumes are necessary to imp rove
power performance in highly trained rugby athletes, 200 and
300 ground impacts can be performed with the same level of
fatigue and neuromuscular impairments as 100 jumps, at least
in the rst 24 hours with long rest intervals between sets, such
as the intervals used in this study (i.e., 5 minutes). However,
caution should be exercised when applying the present results
because the time of recovery was monitored only in the first
24 hours and differences between the plyometric exercise
volumes investigated might appear after this period. F urther-
more, the subjects of this study were elite rugby athletes who
often perform high volumes of plyometric training, and it is
possible that the same pattern of neuromuscular responses
would not be observed in untrained or less trained subjects.
ACKNOWLEDGMENTS
This study was partially supported by the National Council
of Technological and Scientific Development (CNPQ),
Coordination of Improvement of Higher Education Person-
nel (CAPES) and Brazilian Sports Ministry.
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Physiological Responses to Plyometric Exercise
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    • "That is, testosterone transiently increases in boys following both resistance and plyometric exercise. Contrary to the typical adult response (Cadore et al. 2013; Kraemer et al. 1993, Kraemer and Ratamess 2005), cortisol levels gradually decreased from baseline to 5 min post-exercise to a similar extent in both trials. The first part of this response, i.e., the decrease in salivary cortisol during the resting control period, may simply reflect the typical diurnal decrease of cortisol in the evening. "
    [Show abstract] [Hide abstract] ABSTRACT: This study examined changes in salivary testosterone and cortisol following resistance and plyometric exercise protocols in active boys. In a crossover experimental design, 26 peri-pubertal (12- to 14-year-old) soccer players performed 2 exercise trials in random order, on separate evenings, 1 week apart. Each trial included a 30 min control session followed by 30 min of either resistance or plyometric exercise. Saliva was collected at baseline, post-control (i.e., pre-exercise), and 5 and 30 min post-exercise. There were no significant differences in the baseline hormone concentrations between trials or between weeks (p > 0.05). A significant effect for time was found for testosterone (p = 0.02, [Formula: see text] = 0.14), which increased from pre-exercise to 5 min post-exercise in both the resistance (27% ± 5%) and plyometric (12% ± 6%) protocols. Cortisol decreased to a similar extent in both trials (p = 0.009, [Formula: see text] = 0.19) from baseline to post-control and then to 5 min post-exercise, following its typical circadian decrease in the evening hours. However, a significant protocol-by-time interaction was observed for cortisol, which increased 30 min after the plyometrics (+31% ± 12%) but continued to decrease following the resistance protocol (-21% ± 5%). Our results suggest that in young male athletes, multiple modes of exercise can lead to a transient anabolic state, thus maximizing the beneficial effects on growth and development, when exercise is performed in the evening hours.
    Full-text · Article · Mar 2016