Plyometric training is a training method to increase the motor output, stretch-shortening cycle which could be associated with power output. To increase the neuromuscular output, various training variables have been incorporated in training programs. Weight vest is one of the variables to develop it. However, how much load can effectively develop the neural response is still not clearly understood. The aim of this study was to identify the effects of additional external loads on neuromuscular response of lower body during plyometric jump. Total 19 men performed jump tests with weight vest (two jumps in each additional load; 0%, 10%, 15% and 20% of bodyweight [BW]). During the tests, neuromuscular responses of lower extremity were measured. In vertical jump, 0%BW group was higher than the other heavier loads. In rate of force development (RFD), 10%BW was higher than 15%BW and 20%BW. In 0–30 msec of interval RFD, the heavier load groups were greater than 0%BW and in 0–50 msec, 15%BW and 20%BW were higher than 0%BW. In neuromuscular efficiency (NME), 15%BW and 20%BW were greater than 0%BW in ankle joint. This research indicated that plyometric jump with additional load causes greater RFD and NME of lower extremity compared with jump training without additional load. During weight vest plyometric jump, 10%–20% of BW load is advantageous to NME of lower body and 10% of BW load is effective to develop RFD of lower extremity.
Plyometric training is one of popular training methods to enhance sports performance (
Previous researches reported that plyometric training enhances many sports performance variables such as muscle strength, power, vertical jump height, agility, sprint performance, and neuromuscular response (
The SSC is important neuromuscular function to produce power (
To increase the neuromuscular output during plyometric training, various training variables (jump height, landing surface, loads, training tools, etc.) have been incorporated to training programs. Applying additional load was suggested as the best training stimulation to develop power output (
However, it has been reported that during plyometric jump, additional load can increase ground contact time and the delayed contact time is associated with the neuromuscular responses (
Although using additional loads in plyometric training is prevalent, how much load can effectively develop neuromuscular output through plyometric training is still not clearly understood (
Total 20 collegiate male subjects participated in this research. Measurement data of 19 subjects, except for 1 subject who had a problem on jump, was used for analyzing the results of this study (
All subjects performed countermovement jump (CMJ) with weight vest. 4 different external loads (0%, 10%, 15%, and 20% of bodyweight [BW]) were used for this study. 2 CMJ tests at each additional load were carried out. 5-min rest was provided between tests of different additional loads to prevent fatigue from jumps. During the jump tests, peak power was measured using GymAware (Kinetic Performance Technology, Canberra, Australia). Vertical jump height, muscle onset time, rate of force development (RFD) and NME of knee and ankle joints were measured using electromyography (EMG) and motion analysis system.
Muscle activation during CMJ was measured by using a wireless EMG device (BTS FREEEMG 1000, BTS Bioengineering, Milano, Italy). Prior to attachment of electrodes, the skin was shaved and cleaned using alcohol. The electrodes were attached to rectus femoris (knee) and soleus (ankle) of the dominant lower extremity. The EMG data was full-wave rectified and low-pass filtered at 50 Hz. Raw EMG signals were collected with a band-pass filter of 20–500 Hz, sampled at 1,000 Hz and rectified. 3 standard deviation above the mean activity on 100 msec of resting period was used to determine onset time of EMG activity.
Joint moments of knee and ankle and maximal vertical jump height were measured using motion capture analysis. The three-dimensional kinematics of the lower extremity were evaluated during CMJ using eight infrared cameras (250 Hz Oqus 5, Qualisys, Göteborg, Sweden). Qualisys track manager (QTM, Qualisys) was used for collecting data. Markers were attached to greater trochanter (GT), anterior superior iliac spine, iliac crest, posterior superior iliac spine, sacrum, medial/lateral epicondyle of the femur, medial/lateral malleolus, calcaneous and 1st, 2nd, and 5th head metaphalanges of the foot.
RFD was evaluated by two types of RFD: (a) RFD to peak EMG amplitude (RFDpeak) and (b) interval RFDs in time intervals of 0–30, 0–50, and 0–200 msec relative to start of jump (RFDinterval) (
NME was defined as the ratio of joint moment to muscle activation (
Vertical jump height was determined by difference of heights of GT at start position and at maximal jump. To calculate vertical jump height, height of GT at standing position to start jump and maximal height of GT during jump were measured.
Peak power was measured by using GymAware power system (GymAware, Kinetics, Australia). Strap of the device was connected to the waists of the subjects. Maximal value of powers measured during 2 CMJ tests was recorded as peak power value.
All data from this study was analyzed by IBM SPSS ver. 18.0 (IBM Co., Armonk, NY, USA). All values were expressed as mean and standard deviation. One-way analysis of variance (ANOVA) was performed to analyze the difference of neuromuscular responses by additional loads during CMJ. When there are significant differences between groups, least significant difference was carried out for
There were significant differences in vertical jump height among the groups (
During CMJ, peak power was assessed by GymAware power testing system. Peak powers by increase of additional loads were gradually decreased. However, the differences of peak power were not statistically significant (
Muscle onset times of rectus femoris in knee joint and soleus in ankle joint were evaluated during the CMJ tests. The differences in muscle onset times of rectus femoris (
To evaluate RDF by additional loads, RFD to peak EMG amplitude (RFDpeak) and Interval RFD (RFDinterval) were tested. In RFDpeak, it was shown that RFDpeak were significantly different in the rectus femoris during the jump (
In RFDinterval, the ANOVA showed that there were significant differences in RFDinterval of rectus femoris at 0–30 msec (
As shown in
Plyometric training is popular in sports training to develop motor output, SSC which is related to power and force production (
Additional load during plyometric jump, however, can increase a ground contact time and the increased ground contact time decreases neuromuscular function to produce power (
Thus, this study was performed to identify the effects of additional loads on neuromuscular responses of lower body during plyometric jump and to clarify how much additional load works for enhancing the neuromuscular function.
Vertical jump height is typical variable to assess power ability. In this study, vertical heights of the heavier groups were gradually decreased by increase of additional loads of weight vests. It was shown that 0%BW group was higher than the heavier groups (10%BW, 15%BW, and 20%BW).
Heavy additional load seemed to negatively influence on vertical jump. During jump test, the inertia of body increased by added load decreases jumping ability (
Peak power and muscle onset time were not statistically different among the groups. Although there was no significant difference in peak power, it was shown that peak powers in the heavier load groups were reduced. This result also arised from the loads of weight vests. Muscle onset time that is known as effective variable to evaluate how much muscle can quickly activate was assessed during CMJ (
RFD means the development of maximal force in minimal time and has been typically defined as an index to assess explosive strength and neuromuscular function (
In interval RFD (RFDinterval), heavier load groups (10%BW, 15%BW, and 20%BW) were higher than 0%BW group at 0–30 msec and 0–50 msec time intervals (
NME is defined as a ratio of joint moment to muscle activation and is known as an effective variable to evaluate neuromuscular function (
In this study, it was revealed that 15%BW and 20%BW groups were greater than 0%BW group in NME of ankle joint (
In force-length principle, the mechanism can place a joint on the appropriate position where muscle can produce greater force (
By the findings of this study, it can be suggested that additional heavy load during plyometric jump training results in enhancement of RFD and 10% of BW is better as additional load to maximize RFD during CMJ jump compared to the other additional loads. Previous research also reported that plyometric training with using 10%–11% of BW load was effective to enhance a jump ability and power (
This study, however, has some considerations. During the research, jump technique of participants was not controlled. One who has a poor jumping technique might have a problem to control the given loads. Also, percentage of load of weight vest can be changed due to adaptation to training. Thus, additional load has to be monitored and adjusted during plyometric training program.
In conclusion, using additional load during plyometric jump is effective for increase of RFD and NME of lower extremity. Previous studies indicated that weighted-vest jumping is shown to cause development of jump performance in athletic population (
No potential conflict of interest relevant to this article was reported.
The author appreciates the subjects for participating in this study. The helps of Dr Hong, Dr Hahn, Yongsuk, Dr Hinkel-Lipsker, Dr Li, Dr Nakamura, JD, Coach K, and In-young are much appreciated. This research was supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea (NRF-2015S1A5B5A07044575).
Rate of force development (mean±standard deviation) by additional loads. *
Interval rate of force development (mean±standard deviation) by additional loads. *
The characteristics of the subjects
Characteristic | Mean±SD |
---|---|
Age (yr) | 24.37±1.57 |
Height (cm) | 177.24±7.32 |
Weight (kg) | 77.23±11.29 |
%Bodyfat (%) | 16.04±5.33 |
Body mass index (kg/m2) | 24.48±2.79 |
SD, standard deviation.
Vertical jump, peak power, and muscle onset time by additional loads
Variable | 0% | 10% | 15% | 20% | |
---|---|---|---|---|---|
Vertical jump height (cm) | 45.33±4.92 | 41.95±4.35 |
40.69±4.05 |
39.09±3.95 |
10% ( |
0%>15% ( | |||||
20% ( | |||||
10%>15% ( | |||||
| |||||
Peak power (W) | 7,090.05±2,074.10 | 6,218.61±1,825.28 | 5,924.18±1,667.41 | 5,710.50±1,604.81 | NS ( |
| |||||
Muscle onset time (msec) | |||||
Knee (RF) | 254.56±48.99 | 242.29±78.32 | 257.55±72.82 | 253.58±80.26 | NS ( |
Ankle (Sol) | 278.68±75.08 | 292.50±281.58 | 281.58±97.69 | 295.66±78.24 | NS ( |
Values are presented as mean±standard deviation.
NS, not significance; RF, rectus femoris; Sol, soleus.
0% vs. 10%,
10% vs. 15%,
0% vs. 15%,
0% vs. 20%,
Rate of force development (RFD) of knee and ankle by additional loads
Variable | 0% | 10% | 15% | 20% | |||
---|---|---|---|---|---|---|---|
RFDpeak (mV/msec) | Knee | 0.007±0.004 | 0.010±0.011 |
0.005±0.005 | 0.005±0.002 | 10%>15% ( | |
10%>20% ( | |||||||
Ankle | 0.006±0.003 | 0.005±0.003 | 0.005±0.007 | 0.007±0.010 | NS ( | ||
| |||||||
RFDinterval (mV/msec) | Knee | 30 msec | 0.033±0.000 | 0.037±0.006 |
0.036±0.004 |
0.004±0.004 |
10% ( |
0%<15% ( | |||||||
20% ( | |||||||
50 msec | 0.020±0.000 | 0.021±0.003 | 0.022±0.002 |
0.022±0.002 |
0%<10% ( | ||
0%<15% ( | |||||||
100 msec | 0.010±0.000 | 0.011±0.001 | 0.0011±0.001 | 0.011±0.001 | NS ( | ||
200 msec | 0.005±0.000 | 0.006±0.001 | 0.006±0.001 | 0.006±0.001 | NS ( | ||
Ankle | 30 msec | 0.033±0.000 | 0.037±0.009 | 0.038±0.011 | 0.004±0.011 | NS ( | |
50 msec | 0.020±0.000 | 0.022±0.005 | 0.022±0.006 | 0.022±0.006 | NS ( | ||
100 msec | 0.010±0.000 | 0.010±0.002 | 0.011±0.003 | 0.010±0.002 | NS ( | ||
200 msec | 0.005±0.000 | 0.005±0.001 | 0.005±0.001 | 0.006±0.001 | NS ( |
Values are presented as mean±standard deviation.
RFDpeak, RFD to peak EMG amplitude; RFDinterval, interval RFDs in time intervals relative to start of jump; NS, not significance.
0% vs. 10%,
0% vs. 15%.
0% vs. 20%,
10% vs. 15%.
0% vs. 20%,
Neuromuscular efficiency of knee and ankle by additional loads
Neuromuscular efficiency (Nm/mV) | 0% | 10% | 15% | 20% | |
---|---|---|---|---|---|
Knee | 1.15±0.27 | 1.24±0.32 | 1.28±0.32 | 1.30±0.33 | NS ( |
| |||||
Ankle | 1.09±0.16 | 1.22±0.27 | 1.30±0.30 |
1.33±0.34 |
0%<15% ( |
0%<20% ( |
Values are presented as mean±standard deviation.
NS, not significance.
0% vs. 15%,
0% vs. 20%,